As global warming caused by carbon dioxide and depletion of petroleum energy have become global issues, the importance of renewable energy such as biomass, hydrogen, and fuel cells as an alternative to fossil fuels have been emphasized. One of the major barriers to develop renewable energy technology is the low efficiency of materials such as catalyst and oxygen/proton conductor in the biomass conversion, hydrogen production, fuel cell, solar cell, and battery operation. Note that the existing material development has been conducted experimentally through time consuming trial-and-error design, synthesis, and evaluation at the particle level. 

The essential part in the development of high-performance materials is to properly tailor the physical and chemical properties of materials. However, a detailed understanding of how to control the properties of such materials is still lacking, despite its importance in designing and developing novel and cost-effective materials. This is in large part due to the difficulty of direct characterization. Alternatively, computational methods such as quantum mechanics-based Density Functional Theory (DFT is ab-initio calculation, which predicts material properties based solely on physical laws without experimental values) and atomistic modeling approaches have emerged as the powerful and flexible means to unravel the fundamental principles of energy and environmental materials, which may allow the new finding of the breakthrough materials.

Alloying effect can be attributed to: i) the existence of unique mixed-metal surface sites [the so called ensemble (geometric) effect]; ii) electronic state changes due to metal-metal interactions [the so called ligand (electronic) effect]; and iii) strain caused by lattice mismatch between the alloy components [the so called strain effect]. In addition, the presence of low-coordination surface atoms and preferential exposure of specific facets [(111), (100), (110)] in association with the size and shape of nanoparticle catalysts [the so called shape-size-facet effect] can be another important factor for modifying the catalytic activity. Therefore, a clear understanding of these alloying effects is essential for the successful development of effective catalysts.

Using the spin-polarized density functional theory (DFT) calculations, we examined the electrochemical N2 reduction (N2RR) toward NH3 production on the hetero RuM (M = 3d transition metals) double atom catalysts supported on the defective graphene by means of the analysis on the geometric ensemble structure, the N2RR mechanism, the decoupling of strain, dopant and configurational effects and the d-orbital resolved density of state (ORDOS) (dz2, dxz, dyz, dxy, and dx2−y2) on the hetero double atoms. In addition, we computationally screened the novel catalysts by exploring the 4d, 5d and p block metals as the hetero M metals in RuM system. First, we found the significantly enhanced N2RR activity of the inclined pentagon M (Fe, Mn, and Sc) double atom catalysts (RuFe has highest activity) compared to the homo Ru2 double atom catalyst. Our DFT calculations on the interplay of strain, dopant and configurational effects in the inclined pentagon M (Fe, Mn, and Sc) double atom catalysts predicted that (1) the dopant effect was the promoter to improve N2RR activity for RuSc and RuMn, (2) the tensile strain (RuSc) tended to reduce the NH3 productivity via N2RR, while the effect of compressive strain (RuFe, RuMn) was insignificant, (3) the dopant-support interaction induced the unique inclined pentagon M double atom ensemble structure, which leads to the large reduction of the N2RR activity for the hetero RuSc double atom but the activity increase for the hetero RuFe and RuMn cases. Finally, our DFT calculation on the analysis of the p−d (dz2, dxz, dyz, dxy, and dx2−y2) orbital overlap identified the key d orbitals in determining the descriptor (NH2 adsorption energy) for representing N2RR. That is, the orbitals (dz2, dxz , dyz) having the orientation toward z direction in the horizontal Ru2 double atom played an important role in determining NH2 adsorption process, while for the inclined pentagon M double atoms (RuFe, RuSc, RuMn), the dxz and dxy orbitals were found to be essential for the modification of NH2 adsorption energy. Finally, a descriptor based DFT search additionally discovered the promising hetero RuOs and RuIr double atom catalysts. This study highlights that the dopant engineering of hetero double atom catalysts supported on the defective graphene can significantly modify the electrochemical reactivity, particularly by the dopant type and geometric ensemble structure.  

We have engineered the MXene supports to boost the single and homo double atoms of Fe, Ru, and Os for efficient NH3 production via electrochemical nitrogen reduction reaction (N2RR) using DFT calculations. We designed the different MXene surfaces which are composed of nine early transition metals [M2CO2 (M = Cr, Hf, Mo, Nb, Ta, Ti, V, W, Zr)] and examined the activity/stability of single and homo double atoms by calculating the free energy diagram of N2RR, dissolution potential, and agglomeration energy. First, we found that the NH2 adsorption energy is the activity descriptor for representing the NH3 productivity and the density of state near the Fermi level of the single Ru atom is the important factor in determining N2RR activity. Next, our DFT calculation on the descriptor-based computational search for the novel MXene-based catalysts showed that among the chemically and electrochemically stable candidate catalysts, the homo double Ru2/Mo2CO2 catalyst showed the highest NH3 productivity with the high N2RR selectivity over hydrogen evolution reaction. In addition, the best Ru2/Mo2CO2 catalyst exhibited the intermediate density of state near the Fermi level, leading to the optimal descriptor value (NH2 adsorption strength) for NH3 production and in turn the reduction of overpotential for the electrochemical NH3 production. More fundamentally, we identified that the electron density near the Fermi level of these single or double atoms is closely correlated with the electron structure of the cationic metal atoms constituting MXene supports. Our study highlights the rational design of single and homo double atom catalysts by tuning the property of MXene supports, which provides insight into the key factors in enhancing NH3 production at ambient conditions.

• S.-H. Kim, H. C. Song, S.J. Yoo, J. Han*, K.-Y. Lee* and H. C. Ham*, “Impact of Ligand-induced Ensemble Structure of Hetero Double Atom Catalysts in Electrochemical NH3 Production”, Journal of Materials Chemistry A, 10, 6216-6230 (2022) 

• H. C, Song and H. C. Ham*, “Engineering MXene Support to Boost the Activity and Stability of Single and Double Atom Catalysts toward Electrochemical NH3 Production via N2 Reduction”, Chemical Engineering Journal,  470, 144243 (2023)

Despite recent efforts on replacing a noble Pt to less expensive catalysts (such as Pt-Ni and Pt-Co alloys) for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst still remains superior. We have proposed the systematic procedure for designing the Ir3M (M = 3d, 4 d, 5 d transition metal) nanoalloy as Pt alternatives with enhanced ORR activity and stability using density functional theory (DFT). First, we computationally optimized the surface occupied/unoccupied d states and lattice distance of the thermodynamically-stable Ir3M nanoalloy in order to achieve the wanted oxygen affinity for promoting ORR. In the next screening process, the nanoalloy prone to the segregation of inside M atom toward the surface layer was excluded, leading ultimately to the potential candidates such as the pure Ir monolayer on the top of Ir3Cr, Ir3V, Ir3Re, and Ir3Tc alloy cores. The detail mechanism on the enhanced activity in Ir-M alloy was also examined. The design principle of alloy catalysts used in this study can be further extended to the screening of catalytic materials for the application to the next-level electrochemical reaction.

The utilization of carbon-encapsulated Pt or Pt-alloy subnanocluster catalysts for proton exchange membrane fuel cells is a promising strategy to further reduce Pt loadings, enhancing catalytic activity and stability. However, such subnanocluster catalysts with carbon encapsulation remain prospective nanomaterials since they have been rarely explored to date. Here, using spin-polarized density functional theory (DFT) calculation, the carbon-encapsulated Pt and Pt-alloy catalysts (Ptn@C and Pt3M3@C) featuring subnanoclusters are developed. Unlike the dissociative oxygen reduction occurring on a variety of metals, The Pt6@C offered facile four-electron oxygen reduction reaction (ORR) pathway via H2O2 decomposition with low kinetic barrier (0.11 eV) at unique active site (carbon surface), and exhibited improved ORR activity with higher onset potential of 0.60 V over against Pt(111) catalyst (0.52 V). To reduce Pt loading and tune catalytic activity of Pt6@C, the binary Pt3M3 alloy subnanoclusters (M = 3d, 4d and 5d block metals) were introduced. Using activity descriptor (*OOH adsorption energy), the screening of Pt3M3@C candidates was conducted. It suggested new Pt3Co3 (0.62 V), Pt3Rh3 (0.60 V), Pt3Ta3 (0.65 V), Pt3Re3 (0.61 V) alloy subnanoclusters possessing even or better ORR activity relative to Pt6@C. The achievement of high ORR performance was also unveiled through an effective charge transfer from the metal subananocluster to the carbon shell. This leads to the down-shift of pz band center of the carbon sites and in turn the formation of bonding orbital between *OOH and carbon at deeper energy level, which consequently strengthens *OOH adsorption and decreases the overpotential. Our study can provide valuable insight into developing the hybrid metal-carbon catalysts with highly reduced Pt loadings for the efficient ORR as well as other electrocatalysis applications.

• J. Cho, I. Chang, H. S. Park, S. H. Choi, J. H. Jang, H.-J. Kim, S.P. Yoon, S. J. Yoo*, and H. C. Ham*, “Computational and Experimental Design of Active and Durable Ir-based Nanoalloy for Electrochemical Oxygen Reduction Reaction”, Applied Catalysis B: Environmental, 234, 177-185 (2018) 

• S. Shin†, E. Lee†, J. Nam, J. Kwon, Y. Choi, B J. Kim, H. C. Ham*, and H. Lee*, “Carbon-Embedded Pt Alloy Cluster Catalysts with High Activity and Durability for Proton Exchange Membrane Fuel Cells”, Advanced Energy Materials, 14 (29), 2400599 (2024)

• E. Lee, S. Shin, H. Lee* and H. C. Ham*, “High Performance Bimetallic PtM (M=Co, Rh, Ta, Re) Carbon-Metal Hybrid Catalysts Featuring Sub-nanoclusters for the Oxygen Reduction Reaction via Facile H2O2 Decomposition”, Applied Surface Science Advances, 28, 100792 (2025)

• H. C. Ham, D. Manogaran, K.H. Lee, K. Kwon, S.-A. Jin, D.J. You, C. Pak, and G.S. Hwang, “Enhanced Oxygen Reduction Reaction and Its Underlying Mechanism in Pd-Ir-Co Trimetallic Alloys,” The Journal of Chemical Physics (communications), 139, 201104 (2013) 

• C.-E. Kim, D.-H. Lim, J.H. Jang, S.P. Yoon, H.-J. Kim, S. W. Nam, S-. A. Hong, A. Soon and H.C. Ham, “effect of Gold Subsurface Layer on the Surface Activity and Segregation in Pt3M Alloy Catalyst from First-Principles",The Journal of Chemical Physics,142(3), 034707(2015)

We present the role of Pd ensembles in the selective direct synthesis of H2O2 from H2 and O2 on a PdAu alloy surface based on periodic density functional theory calculations. Our calculations demonstrate that H2O2 formation is strongly affected by the spatial arrangement of Pd and Au surface atoms. In particular, Pd monomers surrounded by less active Au atoms that suppress O−O bond scission are primarily responsible for the significantly enhanced selectivity toward H2O2 formation on PdAu alloys compared to that on the monometallic Pd and Au counterparts.

• H. C. Ham, G. S. Hwang, J. Han, S. W. Nam, and T. H. Lim, “Geometric Parameter Effects on Ensemble Contributions to Catalysis: H2O2 Formation from H2 and O2 on AuPd Alloys. A First Principles Study,” Journal of Physical Chemistry C, 114, 14922-14928 (2010)

• H. C. Ham, G. S. Hwang*, J. Han, S. W. Nam, and T. H. Lim, “On the Role of Pd Ensembles in Selective H2O2 Formation on AuPd Alloy Surfaces”, Journal of Physical Chemistry C – Letter,113, 12943-12945 (2009) 

We present a theoretical explanation on how PdAu alloy catalysts can enhance the oxidation of CO molecules based on density functional theory calculations of CO adsorption and oxidation on AuPd/Pd(111) surfaces. Our study suggests that the enhanced activity is largely attributed to the possible existence of “partially-poisoned” Pd ensembles that accommodate fewer CO molecules than Pd atoms. Whereas the oxidation of preadsorbed CO is likely governed by O2 trapping, our study shows that small Pd ensembles such as dimers and compact trimers tend to provide more active sites than larger ensembles; CO adsorbed on a Pd monomer is found to react hardly with O2 to form CO2. In addition, we find the tendency of CO-induced Pd agglomeration, which may in turn facilitate CO oxidation by creating more dimers and compact trimers as compared with the adsorbate-free surface where monomers are likely prevailing.

•  H. C. Ham, J. A. Stephenson, G. S. Hwang*, J Han, S. W. Nam, and T. H. Lim, “Role of small Pd ensemble in boosting CO oxidation in AuPd alloys”, Journal of Physical Chemistry Letter, 3, 566 (2012)

• H. C. Ham, D. Manogaran, G. S. Hwang, J. Han, H.J. Kim, S. W. Nam, and T. H. Lim, “Role of different Pd/Pt Ensembles in Determining CO Chemisorption on Au-based Bimetallic Alloys: A First-Principles Study”, Applied Surface Science, 332(3), 409-418(2015) 

By using spin-polarized density functional theory calculations, we have elucidated the role of heteronuclear interactions in determining the selective H2 formation from HCOOH decomposition on bimetallic Pdshell/Mcore (M = late transition FCC metal (Rh, Pt, Ir, Cu, Au, Ag)) catalysts. We found that the catalysis of HCOOH decomposition strongly depends on the variation of surface charge polarization (ligand effect) and lattice distance (strain effect), which are caused by the heteronuclear interactions between surface Pd and core M atoms. In particular, the contraction of surface Pd–Pd bond distance and the increase in electron density in surface Pd atoms in comparison to the pure Pd case are responsible for the enhancement of the selectivity to H2 formation via HCOOH decomposition. Our calculations also unraveled that the d band center location and the density of states for the d band (particularly dz2, dyz, and dxz) near the Fermi level are the important indicators that explain the impact of strain and ligand effects in catalysis, respectively. That is, the surface lattice contraction (expansion) leads to the downshift (upshift) of d band centers in comparison to the pure Pd case, while the electronic charge increase (decrease) in surface Pd atoms results in the depletion (augmentation) of the density of states for dz2, dyz, and dxz orbitals. Our study highlights the importance of properly tailoring the surface lattice distance (d band center) and surface charge polarization (the density of states for dz2, dyz, and dxz orbitals near the Fermi level) by tuning the heteronuclear interactions in bimetallic Pdshell/Mcore catalysts for enhancing the catalysis of HCOOH decomposition toward H2 production, as well as other chemical reactions.

• J. Cho, S. Lee, J. Han, S.P. Yoon, S. W. Nam, K. Y. Lee and H.C. Ham*, “Role of Heteronuclear Interactions in Selective H2 Formation from HCOOH Decomposition on Pd/M (M=Late Transition FCC Metals) Catalysts”, ACS Catalysis, 7, 2553-2562 (2017) 

• S. Lee, J. Cho, J. H. Jang, J. Han, S. W. Nam, S.P. Yoon, T. H. Lim and H. C. Ham*, “Impact of d-band Occupancy and Lattice Contraction on Selective Hydrogen Production from Formic Acid in the Bimetallic Pd-M(early-transition metal) Catalyst”, ACS Catalysis, 6(1), 134-142 (2016) 

• J. Cho, S. Lee, J. Han, S.P. Yoon, S. W. Nam, S.H. Choi, K. Y. Lee and H.C. Ham*, “Importance of Ligand Effect in Enhanced Dehydrogenation of HCOOH on the Bimetallic Pd/Ag Catalyst from First-Principles”, Journal of Physical Chemistry C, 118, 22254-22560 (2014) 

We unravel the beneficial role of the Zn ensemble (in particular, an a single Zn atom) in the sixfold-coordinated kinked (Cu-vacant) site of the stepped Cu(2 1 1) surface for enhancing the reactivity and durability of catalyst in the CH3OH production from CO2 and H2. For such purpose, by using the density functional theory (DFT) and microkinetic modeling methods, we systematically calculate the catalytic properties (activation energy barrier, turn of frequency (TOF), and rate constant), physical properties (cohesive and formation energy) and electronic structures (local density of state, and local charge distribution) of the different defective Cu sites [such as the stepped, kinked, Zn-substituted stepped Cu(2 1 1) surfaces] and the different Zn ensembles [dimer, and linear ensemble]. First, our DFT calculations exhibit that the Zn atoms at the sevenfold-coordinated site of the Cu(2 1 1) surface tend to be isolated and acts as the modifier to suppress the loss of Cu atoms from the stepped Cu(2 1 1) surface. Second, we find that the catalysis of CH3OH synthesis strongly depends on the type of defects at the Cu(2 1 1) surface. In particular, the single Zn atom-substituted (sevenfold-coordinated) stepped site in the Cu(2 1 1) surface is found to have the superior catalytic activity (TOF = 3.07 × 10−5 s−1 @ P = 75 bar and T = 523 K) toward the CH3OH formation compared to the traditionally-known active Cu(2 1 1) surface (TOF = 2.73 × 10−7 s−1). In contrast, the sixfold-coordinated kinked site is determined to largely slow down the rate of CH3OH production (TOF = 3.34 × 10−15 s−1). The increased catalysis in the Zn-associated stepped site is related to the significant enhancement of the surface affinity toward the adsorbate having the oxygen moiety (especially, HCOO), which leads to the large reduction of the activation energy barrier in the initial energy-demanding CO2 hydrogenation reaction and in turn the improved catalysis of CH3OH synthesis. 

• D.Y. Jo, H. C. Ham* and K. Y. Lee*, “Role of the Zn atomic arrangements in Enhancing the Activity and Stability of the Kinked Cu(211) site in CH3OH Production by CO2 Hydrogenation and Dissociation: First-principles Microkinetic Modeling Study”, Journal of Catalysis, 373, 336-350 (2019)

• D.Y. Jo, H. C. Ham*, and K. Y. Lee*, “Facet-dependent Electrocatalysis in the HCOOH Synthesis from CO2 Reduction on Cu catalyst: A Density Functional Theory Study", Applied Surface Science,  527, 15, 146857 (2020) 

• D.Y. Jo, M. W. Lee, C. H. Kim, J. W. Choung, H. C. Ham* and K. Y. Lee*, “Interplay of Ligand and Strain Effects in CO Adsorption on Bimetallic Cu/M (M=Pt, Pd, Ir, Ni) Catalysts from First-principles: Effect of Different Facets in Catalysis”, Catalysis Today, 359, 57-64 (2021)

The conversion of ethylene glycol (EG) to hydrogen is a critical process for advancing sustainable energy solutions. This study combines machine learning, density functional theory (DFT) simulations, and experimental methods to design and validate a highly efficient Pt3Sc alloy catalyst for hydrogen production. First, the supervised deep neural network model with the 38-dimensional feature vector of catalyst properties and the label of activity descriptor (binding energy of C2H5O2), trained on data sets generated using DFT, was employed to search the alloy catalysts, leading to the identification of the Pt3Zr, Pt3Hf, Pt3Sc, Pt3Ta, Pt3Ti, and Pt3Nb candidates. We further calculated the DFT-based free energy diagram of ML-searched candidates for EG decomposition, which was filtered to the Pt3Sc alloy. Next, DFT-based microkinetic modeling (analyzing 92 elementary reactions) was performed to confirm the enhanced activity of the Pt3Sc(111) surface, which revealed that the Pt3Sc(111) catalyst exhibited nearly triple the activity (turn-of-frequency) of Pt(111) in hydrogen production at a temperature of 500 K. Apparent activation energies were predicted from Arrhenius plots (obtained from microkinetic modeling), yielding a lower energy barrier by 0.21 eV (high-temperature region) and by 0.05 eV (low-temperature region) compared to the Pt(111) case. Finally, experimental validation further demonstrated the superior performance of the Pt3Sc/SiO2 catalyst, which achieved 100% hydrogen selectivity and a higher H2 production rate than Pt/SiO2 during the aqueous phase reforming (APR) of EG. This research marks a significant step forward in hydrogen production technology by integrating data-driven, theoretical, and experimental approaches to identify Pt3Sc as a promising catalyst for hydrogen energy solutions.

There is currently no theoretical study on the hydrogenation of xylose to xylitol on a catalyst's surface, limiting proper understanding of the reaction mechanisms and the design of effective catalysts. In this study, DFT techniques were used for the first time to investigate the mechanisms of xylose to xylitol conversion on five notable transition metal (TM) surfaces: Ru(0001), Pt(111), Pd(111), Rh(111), and Ni(111). Two transition state (TS) paths were investigated: TS Path A and TS Path B. The TS Path B, which was further subdivided into TS Path B1 and B2, was proposed to be the minimum energy path (MEP) for the reaction process. According to our computational results, the MEP for this reaction begins with the structural rearrangement of cyclic xylose into its acyclic form prior to step-wise hydrogenation. The rate-determining step (RDS) on Ru(0001), Pt(111), Pd(111), and Ni(111) was discovered to be the ring-opening process via C–O bond scission of cyclic xylose. On Rh(111), however, the RDS was found to be the first hydrogenation stage, leading to the hydrogenation intermediate. Furthermore, based on the RDS barrier, our results revealed that the activities of the tested TM surfaces follow the trend: Ru(0001) > Rh(111) ≥ Ni(111) > Pd(111) > Pt(111). This result demonstrates the higher activity of Ru(0001) compared to other surfaces used for xylose hydrogenation. It correlates with experimental trends in relation to Ru(0001) superiority and provides the basis for understanding the theoretical design of economical and more active catalysts for xylitol production.

• S. G. Akpe†, J. H. Han†, Y. Kim†, Y. Kim, H. J. Lee, S.J. Yon, J. Kang, E. S. Yoo, S.W. Hwang, H. Sohn*, S. H. Choi*, and H. C. Ham* , “Rational Design of Bimetallic Pt3M (M = transition metals) catalyst for Hydrogen Production via Ethylene Glycol Decomposition: Combined Machine Learning, Density Functional Theory, and Experimental Approach”, ACS Catalysis, accepted (2025) 

• S. G. Akpe, S. H. Choi, and H.C. Ham*,  “Conversion of Cyclic Xylose into Xylitol on the Ru, Pt, Pd, Ni, and Rh Catalysts: A Density Functional Theory Study”, Physical Chemistry Chemical Physics (PCCP), 23 (46), 26195-26208 (2021) (2021 HOT PCCP article selected by Editors)

• S. G. Akpe, S.H. Choi and H.C. Ham*, “First-Principles Study on the Design of Nickel based Bimetallic Catalysts for Xylose to Xylitol conversion”, Physical Chemistry Chemical Physics (PCCP),  26, 352-364 (2024) 

• S. G. Akpe, S.H. Choi and H.C. Ham*, “Direct C‒C bond scission of Xylitol to Ethylene and Propylene Glycol Precursors using Single Atom Catalysts on MgO”, APL materials, 11, 051110 (2023) 

Recent advancements in machine learning (ML) have established it as a versatile platform for accelerating materials discovery, enabling high-throughput screening, structure prediction, and property-significance quantification across various catalyst types and scales. This study presents a comprehensive framework leveraging state-of-the-art ML models for both the forward and inverse design of catalytic materials, trained on datasets generated via quantum mechanics-based density functional theory (DFT) calculations. First, a forward large-scale catalyst screening approach employing graph attention networks (GAT) is demonstrated to guide the development of high-entropy alloy catalysts optimized for active and durable oxygen reduction reactions (ORR). Second, a feedforward artificial neural network (Multilayer Perceptron) is utilized to identify efficient electrochemical nitrogen reduction catalysts for ammonia production, as well as thermal reforming catalysts of ethylene glycol for hydrogen production. Third, the inverse design of biomass reforming catalysts is achieved using generative ML algorithms, specifically diffusion models and generative adversarial networks (GANs). Finally, we demonstrate the capacity of these trained ML models to isolate and identify the crucial physical and chemical descriptors that significantly dictate catalytic activity. By seamlessly integrating DFT with cutting-edge machine learning techniques, this work underscores a potential paradigm shift in catalyst science, offering valuable insights for the future automation and optimization of catalyst design processes.

Catalytic descriptors were studied to design optimum catalysts for the oxidative coupling of methane (OCM) by combining density functional theory (DFT) calculations and actual reaction experiments. SrTiO3 perovskite catalysts, selected for OCM, were modified using metal dopants, and their electronic structures were calculated using the DFT method. The CH3 adsorption energy Eads(CH3) and the oxygen vacancy formation energy Ef(vac) exhibited volcano-type correlations with the C2+ selectivity and O2-consumption for the formation of COx, respectively. The optimum catalytic activity, represented by the C2+ selectivity, was obtained for Eads(CH3) = −2.0 to −1.5 eV, indicating that overly strong adsorption of methyl radicals (or easily dissociated Csingle bondH bonds of methane) and relatively insufficient oxygen supplementation to the catalyst surface improve deep oxidation to CO and CO2. Praseodymium (Pr)- and neodymium (Nd)-doped SrTiO3 catalysts confirm the DFT-predicted optimum electronic structure of the OCM catalysts. 

• S. Lim, J.-W Choi, D.-J. Seo, S. H. Song, H. C. Ham*, and J. -M Ha*, “Combined experimental and density functional theory (DFT) studies on the catalyst design for the oxidative coupling of methane”, Journal of Catalysis, 375, 478-492 (2019)

• L. T. Do†, H. W. Cha†, J-W. Choi, D. J. Suh, C.-J. Yoo, H. Lee, K. H. Kim, C. S. Kim, K. Kim, H. C. Ham*, and J.-M. Ha*, “Adsorbed oxygen atoms for improving the oxidative dehydrogenation of ethane over B-site-doped layered perovskite La2Ti2O7”, Chemical Engineering Journal,  481, 148554, (2024) 

As an extension of single-atom catalysts, the development of double-atom catalysts with high electrocatalytic activity for the oxygen evolution reaction (OER) is vital to facilitate hydrogen production and industrial applications. The CoM (M = 3d, 4d, 5d block metals) homo and double-atom catalysts supported on nitrogen-doped graphene (CoM/N4G) were prepared for electrochemical water oxidation under alkaline conditions, and the electrocatalytic activity was studied through density functional theory (DFT) calculations. The hetero CoCu/N4G double-atom catalyst indicated the highest OER activity with an onset potential of 0.83 V, while the homo Co2/N4G catalyst showed a higher onset potential of 1.69 V. The decoupled strain, dopant, and configurational effects based on the notable differences between the homo Co2/N4G and CoCu/N4G explained the enhanced OER activity, implying that the Cu dopant has a crucial impact on boosting the reactivity by reducing the affinity of reaction intermediates. The enhancement could also be understood from the perspective of the electron structure characteristic through d-orbital resolved density of states (ORDOS) (dz2, dxz, dyz, dxy, and dx2−y2) analysis. From the ORDOS analysis, we found an apparent alteration of the key orbitals between Co2/N4G (dz2, dxz, and dyz) and CoCu/N4G (dz2, dxz, dyz, and dxy) with a substantial change in the overlap ratio (Xd). This theoretical study offers beneficial insights into developing a strategy for efficient OER catalysts utilizing a double-atom structure.

• E. Lee, S. H. Choi and H.C. Ham*, “First-principles Design of Hetero CoM (M=3d,4d, 5d Block Metals) Double Atom Catalysts for Oxygen Evolution Reaction”, Nanoscale Advances, 15 (22), 8432 (2022) 

• M.–G. Kim†, H. J. Lee†,T. K. Lee, E. Lee, H. Jin, J.–H. Park, S. Y. Cho, S. Lee, H. C. Ham*, and S. J. Yoo*, “Iridium Selenium Oxyhydroxide Shell for Polymer Electrolyte Membrane Water Electrolyzer with Low Ir Loading”, ACS Energy Letter, 9 (6), 2876-2884  (2024)

• we calculated the diffusion coefficients of H2O and O2 in graphene and graphene with oxygen functional groups to determine the effect of hydrophobicity (Fig. 5a). The hydrophobic graphene exhibited higher diffusion coefficient values (total: 5.0 × 10−6; water: 3.3 × 10−6; O2: 2.2 × 10−5) than the relatively hydrophilic graphene (total: 1.2 × 10−6; water: 8.3 × 10−7; O2: 1.7 × 10−5).

• M.-G. Kim , T. K. Lee , E. Lee , S. Park , H. J. Lee , H. Jin , D. W. Lee , M.–G. Jeong , H.-G. Jung , K. Im , C. Hu , H. C. Ham , K. H. Song , Y.-E. Sung , Y. M. Lee and S. Yoo*, “Realizing the Potential of Hydrophobic Crystalline Carbon as a Support for Oxygen Evolution Electrocatalysts”, Energy & Environmental Science, 16 (11), 5019-5028 (2023) 

The realization of high-performance oxide-based complementary metal-oxide-semiconductor (CMOS) logic circuits is fundamentally bottlenecked by the severe performance asymmetry between n-type and p-type oxide semiconductors. While n-type metal oxides exhibit excellent electron mobilities and are widely integrated into thin-film transistors (TFTs), finding a high-mobility p-type counterpart remains a critical challenge due to the heavy localization of oxygen 2p orbitals at the valence band maximum (VBM). Tin monoxide (SnO) has emerged as a uniquely promising p-type oxide semiconductor to bridge this gap. Featuring a Sn2+ electronic configuration, the strong spatial hybridization between the chemically active  Sn  5s lone pairs and O 2p orbitals highly disperses the VBM, drastically lowering the hole effective mass and enabling superior intrinsic hole mobility. However, the thermodynamic instability of the  Sn2+ state and prevalent self-compensation by native donor defects severely limit carrier control and operational stability in device architectures.

In this work, we employ advanced Density Functional Theory (DFT) calculations using the HSE06 screened hybrid functional to comprehensively investigate the electronic structure, defect thermodynamics, and carrier transport mechanisms of SnO. We map out the thermodynamic phase stability boundaries of SnO and calculate the formation energies of intrinsic defects (V_Sn, V_O, O_i, and I_Sn) as a function of Fermi energy to clarify the origin of its native p-type conductivity. Furthermore, we screen potential extrinsic dopants and apply epitaxial strain engineering to systematically modulate the Sn  5s – O 2p orbital overlap. Our computational insights provide a vital theoretical framework for suppressing structural defects, mitigating self-compensation, and optimizing hole transport, directly accelerating the design of high-performance p-type oxide TFTs for next-generation logic and switching applications.

• Development of an AI-Assisted Integrated Biomass Fractionation-Conversion Process Technology Based on Renewable Electrification, National Research Foundation(NRF)

• Development of Diffusion-Based Inverse Design Model for Catalysts and Design of Highly Efficient Bifunctional Hybrid Nanostructured Catalysts for Rechargeable Hydrogen Gas Batteries, Mid-career researcher program, National Research Foundation(NRF)

• Development of High-Performance p-Type Novel Materials and Device Systems for Implementing Stackable CMOS Integrated Circuits, Korea Planning & Evaluation Institute of Industrial Technology (KEIT)

• H2 database prepration, Korea Environmental Industry & Technology Institute (KEITI)

• Development of High Performance and Durable Electrodes for Ultrahigh Efficiency (>68%) PEMFC Applications, National Research Foundation(NRF)

• Computational design of sensor materials, Samsung Advanced Institute of Technology (SAIT)

• Computational design of catalysts for NOx, CF4 removal, Samsung Advanced Institute of Technology (SAIT)

• Development of advanced electrode catalyst for PAFC, Doosan Fuel Cell

• Design of ultralow loaded Pt-based catalyst for PEMFC cathode with high-activity and stability using computational chemistry, NRF/Nano and Materials project 

• 1kW class molten carbonate type high temperature water electrolysis cell (MCEC) prototype development, KETEP/Energy technology development project

• Theoretical design of catalysts for hydrogen production from C5 organic compounds, NRF/Hydrogen energy innovation technology development project 

• Computational science-based biodiesel manufacturing acid-base complex catalyst design support research, KIER (Korea Institute of Energy Research)

• Design of proton-based intermediate temperature oxygen-evolution catalyst for water electrolysis and current collector using computational science, NRF/Future Hydrogen Energy project 

• High-efficiency multi-metal sub-nanometer cluster catalyst design for electrochemical ammonia synthesis using machine learning, NRF/ Mid-career researcher program

• Innovative technology for CO2 free hydrogen production using molten catalysts, KIAT/Industrial Technology alchemist project)

• Design of catalyst for alkaline water electrolysis by using DFT calculation, KIST (Korea Institute of Science and Technology)