Publications

[43] "Electrochemically Triggered Dynamics Within a Hybrid Metal-Organic Electrocatalyst ” N. Heidary, M. Morency, D. Chartranc, K. H. Ly, R. Iftimie, N. Kornienko ChemRxiv In Press (2019)

A wide array of systems, ranging from enzymes to synthetic catalysts, exert adaptive motifs to maximize their functionality. In a related manner, select metal-organic frameworks (MOFs) and related systems exhibit structural modulations under stimuli such as the infiltration of guest species. Probing their responsive behavior in-situ is a challenging but important step towards understanding their function and subsequently building from there. In this report, we investigate the dynamic behavior of an electrocatalytic Mn-porphyrin containing MOF system (Mn-MOF). We discover, using a combination of electrochemistry and in-situ probes of UV-Vis absorption, resonance Raman and infrared spectroscopy, a restructuration of this system via a reversible cleavage of the porphyrin carboxylate ligands under an applied voltage. We further show, by combining experimental data and DFT calculations, as a proof of concept, the capacity to utilize the Mn-MOF for electrochemical CO2 fixation and to spectroscopically capture the reaction intermediates in its catalytic cycle. The findings of this work and methodology developed opens opportunities in the application of MOFs as dynamic, enzyme-inspired electrocatalytic systems.




[42] "Heterogeneous Electrocatalytic Reduction of CO2 Promoted by Secondary Coordination Sphere Effects ” J. Li*, Y. Zhang*, N. Kornienko New. J. Chem. In press (2020)

The electrochemical conversion of CO2 to fuels and chemicals is a rapidly growing area of both scientific interest and technological importance. To overcome the challenges of low rates and selectivity on heterogeneous catalysts, efforts are being directed to harness enzyme-mimetic secondary coordination sphere effects to attain a further level of control. These include hydrogen bonding, electrostatics, complexation, and sterics to promote CO2 reduction down a desired pathway on the electrocatalyst surface. This focus review is centered on key advances made in recent years in utilizing secondary coordination sphere effects on heterogeneous catalysts. We discuss how the incorporation rationally designed electrolyte additives, grafted surface ligands, and chemically tuneable porous scaffolds facilitate enhanced reactivity for CO2 reduction and what advances still need to be made in order to elevate this technology from the lab scale to economic feasibility.




[41] "Electrochemical Biomass Valorization on Gold-Metal Oxide Nanoscale Heterojunctions Enables Investigation of both Catalyst and Reaction Dynamics with Operando Surface-Enhanced Raman Spectroscopy ” N. Heidary, N. Kornienko Chem. Sci. In Press (2020)

The electrochemical oxidation of biomass platforms such as 5-hydroxymethylfurfural (HMF) to value-added chemicals is an emerging clean technology. However, mechanistic knowledge of this reaction in an electrochemical context is still lacking and operando studies are even more rare. In this work, we utilize core-shell gold-metal oxide nanostructures which enable operando surface-enhanced Raman spectroelectrochemical studies to simultaneously visualize catalyst material transformation and surface reaction intermediates under an applied voltage. As a case study, we show how the transformation of NiOOH from ~1-2 nm amorphous Ni layers facilitates the onset of HMF oxidation to 2,5-furandicarboxylic acid (FDCA), which is attained with 99% Faradaic efficiency in 1M KOH. In contrast to the case in 1M KOH, NiOOH formation is suppressed, and consequently HMF oxidation is sluggish 10 mM KOH, even at high potentials. Operando Raman experiments elucidate how surface adsorption and interaction dictates product selectivity and how the surface intermediates evolve with applied potential. We further extend our methodology to investigate NiFe, Co, Fe, and CoFe catalysts and demonstrate that high water oxidation activity is not necessarily correlated with excellent HMF oxidation performance and highlight catalytic factors important for this reaction such as reactant-surface interactions and catalysts’ physical and electronic structure.




[40] "Host-guest Chemistry Meets Electrocatalysis: Cucurbit[6]uril on a Au Surface as Hybrid System in CO2 Reduction” A.Wagner, K. H. Ly, N. Heidary I. Szabo T. Foeldes, K. I. Assaf , S. J. Barrow, K. Sokolowski, M. Al-Hada, N. Kornienko, M. F. Kuehnel, E. Rosta, I. Zebgerm W. M. Nau, O. A. Scherman, E. Reisner ACS Catal. In Press (2019)

The rational control of forming and stabilizing reaction intermediates to guide specific reaction pathways remains a major challenge in electrocatalysis. In this work, we report a surface active site engineering approach for modulating electrocatalytic CO2 reduction using the macrocycle cucurbit[6]uril (CB[6]). A pristine gold surface functionalized with CB[6] nanocavities was studied as a hybrid organic-inorganic model system that utilizes host-guest chemistry to influence the heterogeneous electrocatalytic reaction. The combination of surface-enhanced infrared absorption (SEIRA) spectroscopy and electrocatalytic experiments in conjunction with theoretical calculations support capture and reduction of CO2 inside the hydrophobic cavity of CB[6] on the gold surface in aqueous KHCO3 at negative potentials. SEIRA spectroscopic experiments show that the decoration of gold with the supramolecular host CB[6] leads to an increased local CO2 concentration close to the gold interface. Electrocatalytic CO2 reduction on a CB[6]-coated gold electrode indicates differences in the specific interactions between CO2 reduction intermediates within and outside the CB[6] molecular cavity, illustrated by a decrease in CO current density, but almost invariant H2 production compared to unfunctionalized Au. The presented methodology and mechanistic insight will guide future design of molecularly engineered catalytic environments through interfacial host-guest chemistry.






[39] 2020 roadmap on two-dimensional nanomaterials for environmental catalysis ” Y. Yang, M. Wu, X. Zhu, H. Xu, Si Ma, Y. Zhi, H. Xia, X. Liu, J. Pan, J.-Y. Tang, S.-P. Chai, L. Palmisano, F. Parrino, K. Liu, J. Ma, Z.-L. Wang, L. Tan, Y.-F. Zhao, Y.-F. Song, P. Singh, P. Raizada, D. Jiang, Di Li, RA Geioushy, J.Ma, K. Zhang, S. Hu, R. Feng, G. Liu, M. Liu, Z. Li, M. Shao, N. Li, J. Peng, W.-J. Ong, N. Kornienko, Z. Xing, X. Fan, J. Ma . In Press (2019)

Environmental catalysis has drawn a great deal of attention due to its clean ways to produce useful chemicals or carry out some chemical processes. Photocatalysis and electrocatalysis play important roles in these fields. They can decompose and remove organic pollutants from the aqueous environment, and prepare some fine chemicals. Moreover, they also can carry out some important reactions, such as O2 reduction reaction (ORR), O2 evolution reaction (OER), H2 evolution reaction (HER), CO2 reduction reaction (CO2RR), and N2 fixation (NRR). For catalytic reactions, it is the key to develop high-performance catalysts to meet the demand for targeted reactions. In recent years, two-dimensional (2D) materials have attracted great interest in environmental catalysis due to their unique layered structures, which offer us to make use of their electronic and structural characteristics. Great progress has been made so far, including graphene, black phosphorus, oxides, layered double hydroxides (LDHs), chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks (MOFs), covalent organic frameworks (COFs), and others. This content drives us to invite many famous groups in these fields to write the roadmap on two-dimensional nanomaterials for environmental catalysis. We hope that this roadmap can give the useful guidance to researchers in future researches, and provide the research directions.






[38] “Investigation of mixed-metal (oxy)fluorides as a new class of water oxidation electrocatalysts ” K. Lemoine, J. Lhoste, A. Ribaud, N. Heidary, V. Maisonneuve, A. Guiet, N. Kornienko Chem. Sci. In Press (2019)

The development of electrocatalysts for the oxygen evolution reaction (OER) is one of the principal challenges in the area of renewable energy research. Within this context, mixed-metal oxides have recently emerged as the highest performing OER catalysts. Their structural and compositional modification to further boost their activity is crucial to the wide-spread use of electrolysis technologies. In this work, we investigated a series of mixed-metal F-containing materials as OER catalysts to probe possible benefits of the high electronegativity of fluoride ions. We found that crystalline hydrated fluorides, CoFe2F8(H2O)2, NiFe2F8(H2O)2, and amorphous oxyfluorides, NiFe2F4.4O1.8 and CoFe2F6.6O0.7, feature excellent activity and stability for the OER in alkaline electrolyte. Subsequent electroanalytical and spectroscopic characterization hinted that the electronic structure modulation conferred by the fluoride ions aided their reactivity. Finally, the best catalyst of the set, NiFe2F4.4O1.8, was applied as anode in an electrolyzer comprised solely of earth-abundant materials.




[37] “Operando Raman probing of electrocatalytic biomass oxidation on gold nanoparticle surfaces ” N. Heidary, N. Kornienko Chem. Commun. In Press (2019)

Electrocatalytic conversion of biomass-derived intermediates is a green route to value-added chemicals. However, this technology is just emerging and the mechanisms of this process are not fully resolved. Here, we present the first operando Raman spectroscopic investigation of 5-hydroxymethylfurfural oxidation on gold nanoparticle sufaces, opening up avenues for understanding such reactivity and for rational systems design.

[36] “Probing CO2 conversion chemistry on nanostructured surfaces with operando vibrational spectroscopy ” N. Heidary, K. H. Ly, N. Kornienko Nano Lett. In Press (2019)

With the rising emphasis on of renewable energy research, the field of CO2 electrocatalytic conversion to fuels has grown tremendously in recent years. Advances in nanomaterial synthesis and characterization have enabled researchers to screen effects of elemental composition, size, surface chemistry on catalyst performance. However, direct links from structure, active state to catalytic function are difficult to establish. To this end, operando spectroscopic techniques can provide key complementary information by investigating electrocatalysis under operating conditions. In particular, Raman and infrared spectroscopy have potential to reveal the identity of surface-bound intermediates, catalyst active state, and possible reaction sites to supplement the insights extracted from conventional electrochemistry. Such research aims to work in tandem synthetic and catalytic efforts to guide the development of next-generation CO2 electrocatalytic systems through rational design. In this mini-review, we examine the latest developments in operando probing of electrochemical CO2 reduction on nanostructured electrocatalysts and detail how this research accelerates the advancement of this field.


[35] “Advancing Techniques for Investigating the Enzyme-Electrode Interface ” N. Kornienko, K. H. Ly, W. E. Robinson, N. Heidary, J. Z. Zhang, E. Reisner Acc. Chem. Res. In Press (2019)

Complementing standard electrochemical experiments with an orthogonal set of techniques has recently allowed to provide a more complete picture of enzyme-electrode systems. Within this framework, we first discuss a brief history of achievements and challenges in enzyme electrochemistry. We subsequently describe how the aforementioned challenges can be overcome by applying advanced electrochemical techniques, quartz-crystal microbalance measurements, and spectroscopic, namely resonance Raman and infrared, analysis. For example, rotating ring disk electrochemistry allows for the simultaneous determination of reaction kinetics as well as quantification of generated products. In addition, recording changes in frequency and dissipation in a quartz crystal microbalance allows to shed light into enzyme loading, relative orientation, clustering, and denaturation at the electrode surface. Resonance Raman spectroscopy yields information on ligation and redox state of enzyme cofactors, whereas infrared spectroscopy enhances our knowledge on active site states and protein secondary and tertiary structure. The development of these emerging methods for the analysis of the enzyme-electrode interface is the primary focus of this Account. We also take a critical look at the remaining gaps in our understanding and challenges lying ahead towards attaining a complete mechanistic picture of the enzyme-electrode interface.




[34] “Bio-inspired synthesis of reduced graphene oxide wrapped Geobacter sulfurreducens as a novel hybrid electrocatalyst for efficient oxygen evolution reaction ” S. Kalathil, K. Katuri, A. Alzami, P. Pedireddy, N. Kornienko, P. Costa, P. Saikally Chem. Mater. Accepted (2019)

Doping of graphene or reduced graphene oxide (rGO) with heteroatoms provides a promising route for the development of electrocatalysts useful in many technologies, including water splitting. However, current doping approaches are complicated, not eco-friendly and not cost-effective. Herein, we report the synthesis of doped rGO for oxygen evolution reaction (OER) using a simple approach that is cost-effective, sustainable and easy to scale up. The OER catalyst was derived from the reduction of GO by an exo-electron transferring bacterium, Geobacter sulfurreducens. Various analytical tools indicate that OER active elements such as Fe, Cu, N, P, and S dope/decorate the rGO flakes. The hybrid catalyst (i.e., Geobacter/rGO) produces a geometric current density of 10 mA cm−2 at an overpotential of 270 mV vs. the reversible hydrogen electrode with a Tafel slope of 43 mV dec−1, and possesses high durability, evidenced through 10 hours of stability testing. Electrochemical analyses suggest the importance of Fe and its possible role as active site for OER. Overall, this work represents a simple approach towards the development of earth abundant, eco-friendly and highly active OER electrocatalyst for various applications such as solar cells, rechargeable metal-air batteries, and microbial electrosynthesis.

[33] “Interfacing formate dehydrogenase with metal oxides for reversible electrocatalysis or solar-driven reduction of carbon dioxide” M. Miller, W. E. Robinson, A. R. Oliveira, N. Heidary, N. Kornienko, J. Warnan, I. A. C. Pereira, E. Reisner Angew. Chemie. Int. Ed. 141, 4659 (2019)

The integration of enzymes with synthetic materials allows efficient electrocatalysis and solar fuels production. Here, we couple formate dehydrogenase (FDH) from Desulfovibrio vulgaris Hildenborough (DvH) to metal oxides for catalytic CO2 reduction and report an in-depth study of the resulting enzyme-material interface. Protein film voltammetry (PFV) demonstrates stable binding of FDH in an electroactive configuration on metal oxide electrodes and reveals reversible and selective reduction of CO2 to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR IR) spectroscopy confirm a high binding affinity for FDH to the TiO2 surface. Adsorption of FDH on dye-sensitized TiO2 allows for visible-light driven CO2 reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11 ± 1 s−1. The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in selective photoreduction of aqueous CO2 to formate.




[32] “Artificial Photosynthesis with Metal and Covalent Organic Frameworks (MOFs and COFs): Challenges and Prospects in Fuel-Forming Electrocatalysis” N. Heidary, T. G.A.A Harris. K.H. Ly, N. Kornienko Phys. Plant. (2019)

Mimicking photosynthesis in generating chemical fuels from sunlight is a promising strategy to alleviate society’s demand for fossil fuels. However, this approach involves a number of challenges that must be overcome before this concept can emerge as a viable solution to society’s energy demand. Particularly in artificial photosynthesis, the catalytic chemistry that converts energy in the form of electricity into carbon-based fuels and chemicals has yet to be developed. Here, we describe the foundational work and future prospects of an emerging and promising class of materials: metal- and covalent-organic frameworks (MOFs and COFs). Within this context, these porous and tuneable framework materials have achieved initial success in converting abundant feedstocks (H2O and CO2) into chemicals and fuels. In this review, we first highlight key achievements in this direction. We then follow with a perspective on precisely how MOFs and COFs can perform in ways not possible with conventional molecular or heterogeneous catalysts. We conclude with a view on how spectroscopically probing MOF and COF catalysis can be used to elucidate reaction mechanisms and material dynamics throughout the course of reaction.




[31] “Oxygenic Photoreactivity in Photosystem II Studied by Rotating Ring Disk Electrochemistry” N. Kornienko, J. Z. Zhang, K. Ly, K. P. Sokol, A. Fantuzzi, R. van Grondelle, A. W. Rutherford, E. Reisner J. Am. Chem. Soc. 140 (51), pp 17923–17931 (2018)

Protein film photoelectrochemistry has previously been used to monitor the activity of photosystem II, the water-plastoquinone photooxidoreductase, but the mechanistic information attainable from a three-electrode setup has remained limited. Here we introduce the four-electrode rotating ring disk electrode technique for quantifying light-driven reaction kinetics and mechanistic pathways in real time at the enzyme–electrode interface. This setup allows us to study photochemical H2O oxidation in photosystem II and to gain an in-depth understanding of pathways that generate reactive oxygen species. The results show that photosystem II reacts with O2 through two main pathways that both involve a superoxide intermediate to produce H2O2. The first pathway involves the established chlorophyll triplet-mediated formation of singlet oxygen, which is followed by its reduction to superoxide at the electrode surface. The second pathway is specific for the enzyme/electrode interface: an exposed antenna chlorophyll is sufficiently close to the electrode for rapid injection of an electron to form a highly reducing chlorophyll anion, which reacts with O2in solution to produce O2•–. Incomplete H2O oxidation does not significantly contribute to reactive oxygen formation in our conditions. The rotating ring disk electrode technique allows the chemical reactivity of photosystem II to be studied electrochemically and opens several avenues for future investigation.




[30] “Bias-free photoelectrochemical water splitting with photosystem II on a dye-sensitised photoanode wired to hydrogenase” K. P. Sokol, W. E. Robinson, J. Warnan, N. Kornienko, J. Zhang, A. Ruff. E. Reisner, Nature Energy 3, 944–951 (2018)

Semi-artificial photosynthetic systems aim to overcome the limitations of natural and artificial photosynthesis while providing an opportunity to investigate their respective functionality. The progress and studies of these hybrid systems is the focus of this forward-looking perspective. In this Review, we discuss how enzymes have been interfaced with synthetic materials and employed for semi-artificial fuel production. In parallel, we examine how more complex living cellular systems can be recruited for in vivo fuel and chemical production in an approach where inorganic nanostructures are hybridized with photosynthetic and non-photosynthetic microorganisms. Side-by-side comparisons reveal strengths and limitations of enzyme- and microorganism-based hybrid systems, and how lessons extracted from studying enzyme hybrids can be applied to investigations of microorganism-hybrid devices. We conclude by putting semi-artificial photosynthesis in the context of its own ambitions and discuss how it can help address the grand challenges facing artificial systems for the efficient generation of solar fuels and chemicals.




[29] "Semi-artificial photosynthesis: interfacing nature’s catalytic machinery with synthetic materials" Nikolay Kornienko, Jenny Zhang, Kelsey K. Sakimoto, Peidong Yang, Erwin Reisner Nature Nanotechnology 13, 890–899 (2018)

Semi-artificial photosynthetic systems aim to overcome the limitations of natural and artificial photosynthesis while providing an opportunity to investigate their respective functionality. The progress and studies of these hybrid systems is the focus of this forward-looking perspective. In this Review, we discuss how enzymes have been interfaced with synthetic materials and employed for semi-artificial fuel production. In parallel, we examine how more complex living cellular systems can be recruited for in vivo fuel and chemical production in an approach where inorganic nanostructures are hybridized with photosynthetic and non-photosynthetic microorganisms. Side-by-side comparisons reveal strengths and limitations of enzyme- and microorganism-based hybrid systems, and how lessons extracted from studying enzyme hybrids can be applied to investigations of microorganism-hybrid devices. We conclude by putting semi-artificial photosynthesis in the context of its own ambitions and discuss how it can help address the grand challenges facing artificial systems for the efficient generation of solar fuels and chemicals.




[28] "Catalysis by design: development of a bifunctional water splitting catalyst through an operando measurement directed optimization cycle" Nikolay Kornienko, Nina Heidary, Giannantonio Cibin, Erwin Reisner, Chemical Science, 2018, 9, 5322

A critical challenge in energy research is the development of earth abundant and cost-effective materials that catalyze the electrochemical splitting of water into hydrogen and oxygen at high rates and low overpotentials. Key to addressing this issue lies not only in the synthesis of new materials, but also in the elucidation of their active sites, their structure under operating conditions and ultimately, extraction of the structure–function relationships used to spearhead the next generation of catalyst development. In this work, we present a complete cycle of synthesis, operando characterization, and redesign of an amorphous cobalt phosphide (CoPx) bifunctional catalyst. The research was driven by integrated electrochemical analysis, Raman spectroscopy and gravimetric measurements utilizing a novel quartz crystal microbalance spectroelectrochemical cell to uncover the catalytically active species of amorphous CoPx and subsequently modify the material to enhance the activity of the elucidated catalytic phases. Illustrating the power of our approach, the second generation cobalt–iron phosphide (CoFePx) catalyst, developed through an iteration of the operando measurement directed optimization cycle, is superior in both hydrogen and oxygen evolution reactivity over the previous material and is capable of overall water electrolysis at a current density of 10 mA cm−2 with 1.5 V applied bias in 1 M KOH electrolyte solution.


[27] "Aerobic conditions enhance the photocatalytic stability of CdS/CdOx quantum dots" David Wakerley, Khoa Ly, Nikolay Kornienko, Katherine Orchard, Moritz Kuehnel, Erwin Reisner, Chemistry: A European Journal, 24, 1-5 (2018)

Photocatalytic H2 production through water splitting represents an attractive route to generate a renewable fuel. These systems are typically limited to anaerobic conditions due to the inhibiting effects of O2. Here, we report that sacrificial H2 evolution with CdS quantum dots does not suffer from O2 inhibition and can even be stabilised under aerobic conditions. The introduction of O2 prevents a key inactivation pathway of CdS (over‐accumulation of metallic Cd and particle agglomeration) and thereby affords particles with higher stability. These findings represent a route to exploit the O2 reduction reaction to inhibit deactivation, rather than catalysis, offering a strategy to stabilize photocatalysts that suffer from similar degradation reactions.

[26] "Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells" Dong Heon Nam , Jenny Z. Zhang, Virgil Andrei, Nikolay Kornienko, Nina Heidary, Andreas Wagner, Kenichi Nakanishi, Katarzyna P. Sokol, Barnaby Slater, Ingo Zebger, Stephan Hofmann, Juan C. Fontecilla‐Camps, Chan Beum Park , Erwin Reisner, Angewandte Chemie, 57, 10595–10599 (2018)

Hydrogenases (H2ases) are benchmark electrocatalysts in H2 production, both in biology and (photo) catalysis in vitro. We report the tailoring of ap‐type Si photocathode for optimal loading and wiring of H2ase by the introduction of a hierarchical inverse opal (IO) TiO2 interlayer. This proton reducing Si| IO‐TiO2| H2ase photocathode is capable of driving overall water splitting in combination with a complementary photoanode. We demonstrate unassisted (bias‐free) water‐splitting by wiring Si| IO‐TiO2| H2ase to a modified BiVO4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si| IO‐TiO2| H2ase to a photosystem II (PSII) photoanode provides proof‐of‐concept for an engineered Z‐scheme that replaces the non‐complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode.





[25] "Efficient hydrogen peroxide generation using reduced graphene oxide-based oxygen reduction electrocatalysts" Hyo Won Kim, Michael B Ross, Nikolay Kornienko, Liang Zhang, Jinghua Guo, Peidong Yang, Bryan D McCloskey, Nature Catalysis, 2018. 1

Electrochemical oxygen reduction has garnered attention as an emerging alternative to the traditional anthraquinone oxidation process to enable the distributed production of hydrogen peroxide. Here, we demonstrate a selective and efficient non-precious electrocatalyst, prepared through an easily scalable mild thermal reduction of graphene oxide, to form hydrogen peroxide from oxygen. During oxygen reduction, certain variants of the mildly reduced graphene oxide electrocatalyst exhibit highly selective and stable peroxide formation activity at low overpotentials (<10 mV) under basic conditions, exceeding the performance of current state-of-the-art alkaline catalysts. Spectroscopic structural characterization and in situ Raman spectroelectrochemistry provide strong evidence that sp2-hybridized carbon near-ring ether defects along sheet edges are the most active sites for peroxide production, providing new insight into the electrocatalytic design of carbon-based materials for effective peroxide production.




[24] "Enhancing Catalysis through Substitute-Driven Redox Tuning" Nikolay Kornienko Joule 2018 2 (2), 207-209

The shift to a renewable energy powered society will ultimately be driven by the development of effective methods of energy conversion and storage. Energy is most efficiently stored in chemical bonds, and consequently, energy harvesting and storage often requires bond cleavage and formation. Catalysts speed up these reactions to minimize energy losses and voltage requirements in electrochemical processes. To this end, the discovery of efficient and cost-effective catalysts underpins the growth of technologies ranging from fuel cells and electrolyzers to metal-air batteries.

[23] "Physical Biology of the Materials–Microorganism Interface" Kelsey K Sakimoto, Nikolay Kornienko, Stefano Cestellos-Blanco, Jongwoo Lim, Chong Liu, Peidong Yang J. Am. Chem. Soc., 2018, 140 (6), pp 1978–1985

Future solar-to-chemical production will rely upon a deep understanding of the material–microorganism interface. Hybrid technologies, which combine inorganic semiconductor light harvesters with biological catalysis to transform light, air, and water into chemicals, already demonstrate a wide product scope and energy efficiencies surpassing that of natural photosynthesis. But optimization to economic competitiveness and fundamental curiosity beg for answers to two basic questions: (1) how do materials transfer energy and charge to microorganisms, and (2) how do we design for bio- and chemocompatibility between these seemingly unnatural partners? This Perspective highlights the state-of-the-art and outlines future research paths to inform the cadre of spectroscopists, electrochemists, bioinorganic chemists, material scientists, and biologists who will ultimately solve these mysteries.




[22] Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping" T. J Jacobsson , S. Svanström, V. Andrei, J. P. H. Rivett, N. Kornienko, B. Philippe, U. B. Cappel, H. Rensmo, F. Deschler, and G. Boschloo. J. Phys. Chem. C, Article ASAP

A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite CsxFAyMAzRb1-x-y-zPbBrqI3-q. This paper continues this trend by exploring doping of mixed lead halide perovskites, FA0.83MA0.17PbBr0.51I2.49, with an extended set of alkali cations, i.e., Cs+, Rb+, K+, and Na+, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV–vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs+ can replace the organic cations in the perovskite structure, but Rb+, K+, and Na+ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance.




[21] “Reticular Electronic Tuning of Porphyrin Active Sites in Covalent Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction" C. Dierks*, S. Lin*, N. Kornienko, E. Kapustin, E. Nichols, C. Zhu, Y. Zhao, C. Chang, and O. M. Yaghi J. Am. Chem. Soc.. 2017, 140 (3), 1116-1122

The electronic character of porphyrin active sites for electrocatalytic reduction of CO2 to CO in a two-dimensional covalent organic framework (COF) was tuned by modification of the reticular structure. Efficient charge transport along the COF backbone promotes electronic connectivity between remote functional groups and the active sites and enables the modulation of the catalytic properties of the system. A series of oriented thin films of these COFs was found to reduce CO2 to CO at low overpotential (550 mV) with high selectivity (faradaic efficiency of 87%) and at high current densities (65 mA/mg) ― a performance well beyond related molecular catalysts in regard to selectivity and efficiency. The catalysts are stable for over 12 hours without any loss in reactivity. X-ray absorption measurements on the cobalt L-edge for the modified COFs enable correlations between the inductive effects of the appended functionality and the electronic character of the reticulated molecular active sites.




[20] “Critical Role of Methylammonium Librational Motion in Methylammonium Lead Iodide (CH3NH3PbI3) Perovskite Photochemistry" M. Park*, N. Kornienko*, S. E. Reyes-Lillo, M. Lai, J. B. Neaton, P. Yang, and R. A. Mathies Nano Lett. 2017, 17 (7), pp 4151–4157

Raman and photoluminescence (PL) spectroscopy are used to investigate dynamic structure-function relationships in methylammonium lead iodide (MAPbI3) perovskite. The intensity of the 150 cm-1 methylammonium (MA) librational Raman mode is found to be correlated with PL intensities in microstructures of MAPbI3. Because of the strong hydrogen-bond between hydrogens in MA and iodine in the PbI6 perovskite octahedra, the Raman activity of MA is very sensitive to structural distortions of the inorganic framework. The structural distortions directly influence PL intensities, which in turn, have been correlated with microstructure quality. Our measurements, supported with first principles calculations, indicate how excited-state MA librational displacements mechanistically control PL efficiency and lifetime in MAPbI3 - material parameters that are likely important for efficient PV devices.




[19] “Cyborgian Material Design for Solar Fuel Production: The Emerging Photosynthetic Biohybrid Systems” K. Sakimoto, N. Kornienko, P. Yang Acc. Chem. Res.. 2017 50 (3), 476-481

Photosynthetic Biohybrid Systems (PBSs),combine the strengths of inorganic materials and biological catalysts:exploiting semiconductor broadband light absorption to capture solar energy and subsequently transform it into valuable CO2-derived chemicals by taking advantage of the metabolic pathways in living organisms.

In this work, we first traverse through a brief history of recent PBSs, demonstrating the modularity and diversity of possible architectures to rival and, in many cases, surpass the performance of chemistry or biology alone before envisioning the future of these hybrid systems, opportunities for improvement, and its role in a sustainable living here on earth, and beyond.



[18] “Spectroscopic elucidation of energy transfer in hybrid inorganic–biological organisms for solar-to-chemical production” N. Kornienko*, K. Sakimoto*, D. Herlihy, S. Nguyen, A. P. Alivisatos, C. B. Harris, A. Schwartzberg, P. Yang Proc. Natl. Acad. Sci. 113, 42 (2016)

Solar-powered chemical production from CO2 promises to alleviate petrochemical consumption. Hybrid systems of an inorganic semiconductor light harvester and a microbial catalyst offer a viable way forward. Whereas a number of such systems have been described, the semiconductor-to-bacterium electron transfer mechanism remains largely unknown, limiting rational approaches to improving their performance. In this work, we look at how a semiconductor nanoparticle-sensitized bacterium transforms CO2 and sunlight into acetic acid, a known precursor for fuels, food, pharmaceuticals, and polymers. Using time-resolved spectroscopy and biochemical analysis, we conclude that multiple pathways facilitate electron and light energy transfer from semiconductor to bacterium. This foundational study enables future investigation, understanding, and improvement of complex biotic–abiotic hybrid systems.

In the News: LBL Highlight




[17] “Atomic Resolution Imaging of Halide Perovskites” Y. Yu, D. Zhang, C. Kisielowski, L. Dou, N. Kornienko, Y. Bekenstein, A. P. Alivisatos, P. Yang, Nano Lett. 16, 7530 (2016)

The radiation-sensitive nature of halide perovskites has hindered structural studies at the atomic scale. We overcome this obstacle by applying low dose-rate in-line holography, which combines aberration-corrected high-resolution transmission electron microscopy with exit-wave reconstruction. This technique successfully yields the genuine atomic structure of ultrathin two-dimensional CsPbBr3 halide perovskites, and a quantitative structure determination was achieved atom column by atom column using the phase information of the reconstructed exit-wave function without causing electron beam-induced sample alterations. An extraordinarily high image quality enables an unambiguous structural analysis of coexisting high temperature and low temperature phases of CsPbBr3 in single particles. On a broader level, our approach offers unprecedented opportunities to better understand halide perovskites at the atomic level as well as other radiationsensitive materials.

In the News: LBL Highlight




[16] “Synthesis and Composition Tunable Cesium Lead Halide Nanowires through Anion-Exchange Reactions” D. Zhang, Y. Yang, Y. Yu, N. Gibson, A. Wong, S. Eaton, N. Kornienko, Q. Kong, M. Lai, Y. Bekenstein, A. P. Alivisatos, S. R. Leone, P. Yang, J. Am. Chem. Soc. 138, 7326 (2016)

Here, we demonstrate the successful synthesis of brightly emitting colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) nanowires (NWs) with uniform diameters and tunable compositions. By using highly monodisperse CsPbBr3 NWs as templates, the NW composition can be independently controlled through anion-exchange reactions. CsPbX3 alloy NWs with a wide range of alloy compositions can be achieved with well-preserved morphology and crystal structure. The NWs are highly luminescent with photoluminescence quantum yields (PLQY) ranging from 20% to 80%. The bright photoluminescence can be tuned over nearly the entire visible spectrum. The high PLQYs together with charge transport measurements exemplify the efficient alloying of the anionic sublattice in a one-dimensional CsPbX3 system. The wires increased functionality in the form of fast photoresponse rates and the low defect density suggest CsPbX3 NWs as prospective materials for optoelectronic applications.

In the News: LBL Highlight




[15] “Anisotropic Phase Segregation and Migration of Pt in Nanocrystals En Route to Nanoframe Catalysts” Z. Niu, B. Becknell, Y. Yu, D. Kim, C. Chen, N. Kornienko, G. Somorjai, P. Yang, Nature Materials 15, 1188 (2016)

Compositional heterogeneity in shaped, bimetallic nanocrystals offers additional variables to manoeuvre the functionality of the nanocrystal. However, understanding how to manipulate anisotropic elemental distributions in a nanocrystal is a great challenge in reaching higher tiers of nanocatalyst design. Here, we present the evolutionary trajectory of phase segregation in Pt–Ni rhombic dodecahedra. The anisotropic growth of a Pt-rich phase along the 111 directions at the initial growth stage results in Pt segregation to the 14 axes of a rhombic dodecahedron, forming a highly branched, Pt-rich tetradecapod structure embedded in a Ni-rich shell. With longer growth time, the Pt-rich phase selectively migrates outwards through the 14 axes to the 24 edges such that the rhombic dodecahedron becomes a Pt-rich frame enclosing a Ni-rich interior phase. The revealed anisotropic phase segregation and migration mechanism offers a radically different approach to fabrication of nanocatalysts with desired compositional distributions and performance.

In the News: LBL Highlight, Nature Energy Highlight




[14] “Growth and Photoelectrochemical Energy Conversion of Wurtzite Indium Phosphide Nanowire Arrays” N. Kornienko, N. Gibson, H. Zhang, S. W. Eaton, S. Aloni, S. Leone, P. Yang, ACS Nano, 10, 5526 (2016)

Photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising strategy to absorb solar energy and directly convert it into a dense storage medium in the form of chemical bonds. The continual development and improvement of individual components of PEC systems is critical toward increasing the solar to fuel efficiency of prototype devices. Within this context, we describe a study on the growth of wurtzite indium phosphide (InP) nanowire (NW) arrays on silicon substrates and their subsequent implementation as light-absorbing photocathodes in PEC cells. The high onset potential (0.6 V vs the reversible hydrogen electrode) and photocurrent (18 mA/cm2) of the InP photocathodes render them as promising building blocks for high performance PEC cells. As a proof of concept for overall system integration, InP photocathodes were combined with a nanoporous bismuth vanadate (BiVO4) photoanode to generate an unassisted solar water splitting efficiency of 0.5%.

In the News: LBL Highlight




[13] “Single Nanowire Photoelectrochemistry” Y. Su, C. Liu, S. Brittman, J. Tang, A. Fu, N. Kornienko, Q. Kong, P. Yang, Nature Nanotechnology 11, 609 (2016)

Photoelectrochemistry is one of several promising approaches for the realization of efficient solar-to-fuel conversion. Recent work has shown that photoelectrodes made of semiconductor nano-/microwire arrays can have better photoelectrochemical performance than their planar counterparts because of their unique properties, such as high surface area. Although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochemical performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Here, we show that a single-nanowire-based photoelectrode platform can be used to reliably probe the current–voltage (I–V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diameters of individual nanowires, and we find that the flux over the entire nanowire surface (7–30 electrons nm–2 s–1) is significantly reduced as compared with that of a planar analogue (∼1,200 electrons nm–2 s–1). Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.

In the News: LBL Highlight, Nanotech.web




[12] “TiO2/BiVO4 Heterostructure Photoanodes Based on Type II Band Allignment” J. Resarco, H. Zhang, N. Kornienko, N. Becknell, H. Lee, J. Guo, A. Briseno, P. Yang, ACS Cent. Sci. 2, 80 (2016)

Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.

In the News: Wissehschaft, Science Daily, Popular Mechanics, IEEE


[11] “Low-Temperature Solution-Phase Growth of Silicon and Silicon Containing Alloys” J. Sun, F. Cui, C. Kiseilowski, Y. Yu, N. Kornienko, P. Yang, J. Phys. Chem. C. In Press - 2016 DOI: 10.1021/acs.jpcc.5b08289

Low-temperature synthesis of crystalline silicon and silicon-containing nanowires remains a challenge in synthetic chemistry due to the lack of sufficiently reactive Si precursors. We report that colloidal Si nanowires can be grown using tris(trimethylsilyl)silane or trisilane as the Si precursor by a Ga-mediated solution–liquid–solid (SLS) approach at temperatures of about 200 °C, which is more than 200 °C lower than that reported in the previous literature. We further demonstrate that the new Si chemistry can be adopted to incorporate Si atoms into III–V semiconductor lattices, which holds promise to produce a new Si-containing alloy semiconductor nanowire. This development represents an important step toward low-temperature fabrication of Si nanowire-based devices for broad applications.




[10] “Atomic Level Structure of P3Ni Nanoframe Electrocatalysts by In-Situ X-Ray Absorption Spectroscopy” N. Becknell, Y. Kang, C. Chen, J. Resasco, N. Kornienko, J. Guo, N. Markovic, G. Somorjai, V. Stamenkovic, P. Yang, J. Am. Chem. Soc. 37, 15817 (2015)

Understanding the atomic structure of a catalyst is crucial to exposing the source of its performance characteristics. It is highly unlikely that a catalyst remains the same under reaction conditions when compared to as-synthesized. Hence, the ideal experiment to study the catalyst structure should be performed in situ. Here, we use X-ray absorption spectroscopy (XAS) as an in situ technique to study Pt3Ni nanoframe particles which have been proven to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). The surface characteristics of the nanoframes were probed through electrochemical hydrogen underpotential deposition and carbon monoxide electrooxidation, which showed that nanoframe surfaces with different structure exhibit varying levels of binding strength to adsorbate molecules. It is well-known that Pt-skin formation on Pt–Ni catalysts will enhance ORR activity by weakening the binding energy between the surface and adsorbates. Ex situ and in situ XAS results reveal that nanoframes which bind adsorbates more strongly have a rougher Pt surface caused by insufficient segregation of Pt to the surface and consequent Ni dissolution. In contrast, nanoframes which exhibit extremely high ORR activity simultaneously demonstrate more significant segregation of Pt over Ni-rich subsurface layers, allowing better formation of the critical Pt-skin. This work demonstrates that the high ORR activity of the Pt3Ni hollow nanoframes depends on successful formation of the Pt-skin surface structure.





[9] “Atomically Thin Two-Dimensional Organic-Inorganic Hybrid Perovskites” L. Duo, A. Wong, Y. Yu, M. Lai, N. Kornienko, S. Eaton, A. Fu, C. Bishak, J. Ma, T. Ding, N. Ginsberg, L. Wang, A. Alivisatos, P. Yang, Science, 349, 6255 (2015)

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

In the News: Nature Highlight, Kurzweil, Cleantechnica, EE Times, Nanowerk, LBL, AZOM, R&D Magazine, Health Medicine Network, Nanotechnology Now, e Science News, ECN Magazine, Newswise, Materials Today, CE Magazine, Science Newsline, Phys.org, Science Daily, Eureka Alert, Chemistry World




[8] “Metal-Organic Frameworks for Electrocatalytic Reduction of Carbon Dioxide” N. Kornienko*, Y. Zhao*, C. Kley, C. Zhu, D. Kim, S. Lin, C. Chang, O. Yaghi, P. Yang,J. Am. Chem. Soc., 137, 14129 (2015)

A key challenge in the field of electrochemical carbon dioxide reduction is the design of catalytic materials featuring high product selectivity, stability, and a composition of earth-abundant elements. In this work, we introduce thin films of nanosized metal–organic frameworks (MOFs) as atomically defined and nanoscopic materials that function as catalysts for the efficient and selective reduction of carbon dioxide to carbon monoxide in aqueous electrolytes. Detailed examination of a cobalt–porphyrin MOF, Al2(OH)2TCPP-Co (TCPP-H2 = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate) revealed a selectivity for CO production in excess of 76% and stability over 7 h with a per-site turnover number (TON) of 1400. In situ spectroelectrochemical measurements provided insights into the cobalt oxidation state during the course of reaction and showed that the majority of catalytic centers in this MOF are redox-accessible where Co(II) is reduced to Co(I) during catalysis.

In the News: ALS Highlight




[7] “Covalent Organic Frameworks Comprising Cobalt Porphyrins for Catalytic CO2 Reduction in Water” S. Lin*, C. Dierks*, Y. Zhang*, N. Kornienko, E. Nichols, Y. Zhao, A. Paris, D. Kim, P. Yang, O. Yaghi, C. Chang, Science, 349, 1208 (2015)

Conversion of carbon dioxide (CO2) to carbon monoxide (CO) and other value-added carbon products is an important challenge for clean energy research. Here we report modular optimization of covalent organic frameworks (COFs), in which the building units are cobalt porphyrin catalysts linked by organic struts through imine bonds, to prepare a catalytic material for aqueous electrochemical reduction of CO2 to CO. The catalysts exhibit high Faradaic efficiency (90%) and turnover numbers (up to 290,000, with initial turnover frequency of 9400 hour−1) at pH 7 with an overpotential of –0.55 volts, equivalent to a 26-fold improvement in activity compared with the molecular cobalt complex, with no degradation over 24 hours. X-ray absorption data reveal the influence of the COF environment on the electronic structure of the catalytic cobalt centers.

In the News: LBL Highlight, Kurzweil, Newswise, Materials Today, Smithsonian Magazine, e Science News, Eureka Alert, phys.org, Conservation Magazine, Technology.org, Innovations Reports, ECN Magazine, Nanowerk, Lab Manager




[6] “Operando Spectroscopic Analysis of an Amorphous Cobalt Sulfide Electrocatalyst” N. Kornienko, J. Resasco, N. Becknell, C. Jiang, Y. Liu, K. Nie, X. Sun, J. Guo, S. Leone, P. Yang, J. Am. Chem. Soc., 137, 7448 (2015)

The generation of chemical fuel in the form of molecular H2 via the electrolysis of water is regarded to be a promising approach to convert incident solar power into an energy storage medium. Highly efficient and cost-effective catalysts are required to make such an approach practical on a large scale. Recently, a number of amorphous hydrogen evolution reaction (HER) catalysts have emerged that show promise in terms of scalability and reactivity, yet remain poorly understood. In this work, we utilize Raman spectroscopy and X-ray absorption spectroscopy (XAS) as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst. Ex situ measurements reveal that the as-deposited CoSx catalyst is composed of small clusters in which the cobalt is surrounded by both sulfur and oxygen. Operando experiments, performed while the CoSx is catalyzing the HER, yield a molecular model in which cobalt is in an octahedral CoS2-like state where the cobalt center is predominantly surrounded by a first shell of sulfur atoms, which, in turn, are preferentially exposed to electrolyte relative to bulk CoS2. We surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.




[5] “Solution Phase Synthesis of Indium Gallium Phosphide Alloy Nanowires” N. Kornienko, D. Whitmore, Y. Yu, S. Leone and P. Yang, ACS Nano, 9, 3951 (2015)

The tunable physical and electronic structure of III–V semiconductor alloys renders them uniquely useful for a variety of applications, including biological imaging, transistors, and solar energy conversion. However, their fabrication typically requires complex gas phase instrumentation or growth from high-temperature melts, which consequently limits their prospects for widespread implementation. Furthermore, the need for lattice matched growth substrates in many cases confines the composition of the materials to a narrow range that can be epitaxially grown. In this work, we present a solution phase synthesis for indium gallium phosphide (InxGa1–xP) alloy nanowires, whose indium/gallium ratio, and consequently, physical and electronic structure, can be tuned across the entire x = 0 to x = 1 composition range. We demonstrate the evolution of structural and optical properties of the nanowires, notably the direct to indirect band gap transition, as the composition is varied from InP to GaP. Our scalable, low-temperature synthesis affords compositional, structural, and electronic tunability and can provide a route for realization of broader InxGa1–xP applications.




[4] “Mesoscopic Constructs of Ordered and Oriented Metal-Organic Frameworks on Plasmonic Silver Nanocrystals” Y. Zhao*, N. Kornienko*, Z. Liu,C. Zhu, S. Asahina, T. Kuo, W. Bao, C. Xie, O. Terasaki, P. Yang, O. Yaghi, J. Am. Chem. Soc., 137, 2199, 2015

We enclose octahedral silver nanocrystals (Ag NCs) in metal–organic frameworks (MOFs) to make mesoscopic constructs Oh-nano-Ag⊂MOF in which the interface between the Ag and the MOF is pristine and the MOF is ordered (crystalline) and oriented on the Ag NCs. This is achieved by atomic layer deposition of aluminum oxide on Ag NCs and addition of a tetra-topic porphyrin-based linker, 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoic acid (H4TCPP), to react with alumina and make MOF [Al2(OH)2TCPP] enclosures around Ag NCs. Alumina thickness is precisely controlled from 0.1 to 3 nm, thus allowing control of the MOF thickness from 10 to 50 nm. Electron microscopy and grazing angle X-ray diffraction confirm the order and orientation of the MOF by virtue of the porphyrin units being perpendicular to the planes of the Ag. We use surface-enhanced Raman spectroscopy to directly track the metalation process on the porphyrin and map the distribution of the metalated and unmetalated linkers on a single-nanoparticle level.





[3]"Visible Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene Isoquinoline Complex”, V Thoi*, N. Kornienko*, C Margarit, P. Yang and C. Chang, J. Am. Chem. Soc., 135, 14413 (2013).

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene–amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = −1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s–1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.




[2] "Reflectivity Enhanced Two-Dimensional Dielectric Particle Array Monolayer Diffraction", A. Tikhonov, N. Kornienko, J. Zhang, L. Wang and S.A. Asher, J. Nanophoton., 6, 063509 (2012).

Very high diffraction efficiencies (>80%>80%) were observed from two-dimensional (2-D) photonic crystals made of monolayers of ∼490 nm∼490 nm diameter dielectric polystyrene spheres arranged in a 2-D hexagonal lattice on top of a liquid mercury surface. These almost close packed 2-D polystyrene particle arrays were prepared by a self-assembly spreading method that utilizes solvent evaporation from the mercury surface. Two-dimensional arrays transferred onto a dielectric glass substrate placed on top of metal mirrors show diffraction efficiencies of over 30%, which is 6- to 8-fold larger than those of the same 2-D monolayers in the absence of mirrors. A simple single particle scattering model with refraction explains the high diffraction efficiencies in terms of reflection of the high intensity forward diffraction.



[1] "2-D Array Photonic Crystal Sensing Motif”, J. Zhang, L. Wang, J. Luo, A. Tikhonov, N. Kornienko, and S.A. Asher, J. Am. Chem. Soc., 133, 9152 (2011).

We have developed the first high-diffraction-efficiency two-dimensional (2-D) photonic crystals for molecular recognition and chemical sensing applications. We prepared close-packed 2-D polystyrene particle arrays by self-assembly of spreading particle monolayers on mercury surfaces. The 2-D particle arrays amazingly diffract 80% of the incident light. When a 2-D array was transferred onto a hydrogel thin film showing a hydrogel volume change in response to a specific analyte, the array spacing was altered, shifting the 2-D array diffraction wavelength. These 2-D array photonic crystals exhibit ultrahigh diffraction efficiencies that enable them to be used for visual determination of analyte concentrations.