Nano & Electronic Materials Lab.

In this study, we propose a simple method for developing bimetallic Fe/M-N4/N-doped porous carbon (NPC) (M-Zn or Mg) conductive metal-organic framework (c-MOF) composites because of their great potential in replacing conventional catalysts. The prepared composite MOF exhibits remarkable catalytic activity for both HER and ORR, surpassing the performance of the state-of-the-art TM-N4 cathode catalysts. These composites demonstrate excellent selectivity for a four-electron transfer, facilitated by an associative reaction pathway that functions as the rate-determining step. Therefore, they offer high half-wave and onset potential values for ORR, i.e., 0.92 and 1.02 V for HAB-3@NPC at a current density of 4.11 mA cm−2, and 0.89 and 0.99 V for HAB-2@NPC at a current density of 3.8 mA cm−2, respectively. In addition, they provide low overpotentials of 21 and 64 mV at the current density of 10 mA cm−2 with Tafel slopes of 47.9 and 34.2 mV/dec for HER, respectively. Furthermore, when utilized as the cathode in bifunctional electrode assembly cells, they provide low cell voltages of 1.412 V at a current density of 20 mAcm−2. In the membrane electrode assembly, the HAB-3@NPC composite demonstrates an optimal power density of 0.861 Wcm−2, thus underscoring its potential in practical applications.

The choice of efficient, stable, and low-cost electrocatalysts is important for oxygen evolution reaction (OER) during water splitting due to its sluggish nature. A bimetallic ZnO-Ni(OH)2 composite has been reported for OER. The composite has been synthesized through the polyvinylpyrrolidone (PVP) and dopamine (DA) assisted simple hydrothermal process. The growth modification ability of PVP and adhesive property of polydopamine from DA were utilized to obtain a 3D interconnected structure. The precursor concentrations were varied to obtain most efficient catalyst [ZNDP-1].  In alkaline medium, ZNDP-1 showed a low over potential of 170 mV (@10 mAcm-2 current density) and a Tafel slope of 61 mVdec-1 with significant stability. The surface defects, porosity and synergism within metal centers might cause efficient electrocatalytic activity. Furthermore, the theoretical studies were performed to understand the mechanistic pathway. The DFT calculations indicated a 4e- transfer mechanism for OER which might proceed through ZnO site. 

We successfully fabricated CDs from para-phenylenediamine (p-PD) and NTA nitrilotriacetic acid (NTA) as novel precursors. The CDs fabricated in this study showed excitation wavelength-independent behavior and solvent-dependent multicolor emission. The relation between polarity of solvents and optical properties of CDs was systematically studied by using various organic solvents. The CDs fabricated in this study exhibited strong solvatochromatic properties, which were then applied in the quantitative analysis of many different amounts of water in the various organic solvents. In addition, a prototype of a paper-strip humidity sensor was successfully fabricated.

Highly fluorescent N-doped carbon dots (NCDs) were fabricated using pyromellitic acid (PA) and ethylene diamine (EDA) as novel precursors. The NCDs exhibited excellent fluorescent properties with a quantum yield as high as 75% due to the enhancement effect of the N dopant on the surface of the NCDs. Moreover, owing to its strong cyan fluorescence, the newly synthesized NCDs were applied effectively as a fluorescence platform for the sensitive and selective determination of 4-nitrophenol (4-NP) without further chemical modification. The NCDs fabricated in this study exhibited a wide linear range, low detection limit, and excellent selectivity towards other organic compounds.

First time, four distinct types of Lead Magnesium Titanate (PMT) perovskites including spheres, flakes, hierarchical flower and thin microbelts shaped were finely tuned via facile solution method to develop cost effective and high performance photoanode material for water splitting. The influence of solvent effects during structural tuning, purity, morphology, optical obsorption, structural phase transition and stoichiometric formation of prepared Lead Magnesium Titanate perovskites has been discussed in detail. Remarkably, thin microbelts structured PMT perovskite (PMTT) exhibited an excellent water splitting performance and it is more sensitive to the illuminated visible light. Owing to the unique structural features, the photoconversion efficiency value of PMTT perovskite is ~3.9, 3.54, 2.85 and 1.52 times higher than those of other prepared PMT perovskites including pristine PbTiO3. The excellent water splitting performance of PMTT (thin microbelts) may be ascribed to the remarkable structural features that include a large surface area, high optical absorbance, more active sites and high interface area of the microbelts, which provide large contact areas between the electrolyte and highly active materials for electrolyte diffusion and a rapid route for charge transfer with minimal diffusion resistance. In addition, each thin microbelt is directly in contact with the Ni foam substrate, which can also shorten the diffusion path for the electrons. The demonstrated approach paves the way to significantly low-cost and high-throughput production of next generation, high performance and highly active water splitting perovskite photocatalyst.

This research presents the first report of the excellent bifunctional electro-catalytic activity and durability of a structure that consists of a highly active inner core of a ruthenium metal organic framework with a mesoporous silica based shell covered with templated CdS nanoparticle electro-catalysts and reduced graphene oxide nano sheets. Excellent electro-catalytic activity toward both the oxygen reduction and oxygen evolution reactions is achieved by selecting a highly active core-shell of silica with CdS and rGO nano-sheets as co-catalysts. In particular, the excellent catalytic activity of the 2 wt. % rGO/CdS/ silica nanocapsule catalyst for both reactions can be attributed to the large surface area and mesoporous nature because they facilitate facile electrochemical activity, and lower the overpotentials and smaller Tafel values than other catalysts. In addition, it is more tolerant to methanol fuel crossover than commercial Pt/C, and exhibits long-term durability.