In this Review, we discuss the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions. Understanding and mastering the kinetics of oxygen electrocatalysis is instrumental to making use of photosynthesis, advancing solar fuels, fuel cells, electrolyzers, and metal–air batteries. We first present key insights, assumptions and limitations of well-known activity descriptors and reaction mechanisms in the past four decades. The turnover frequency of crystalline oxides as promising catalysts is also put into perspective with amorphous oxides and photosystem II. Particular attention is paid to electronic structure parameters that can potentially govern the adsorbate binding strength and thus provide simple rationales and design principles to predict new catalyst chemistries with enhanced activity. We share new perspective synthesizing mechanism and electronic descriptors developed from both molecular orbital and solid state band structure principles. We conclude with an outlook on the opportunities in future research within this rapidly developing field.

/pdf/toward-the-rational-design-of-non-precious-transition-metal-462cs631ks.pdf

Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis

The electrocatalytic hydrogen-evolution reaction (HER), as the main step of water splitting and the cornerstone of exploring the mechanism of other multi-electron transfer electrochemical processes, is the subject of extensive studies. A large number of high-performance electrocatalysts have been developed for HER accompanied by recent significant advances in exploring its electrochemical nature. Herein we present a critical appraisal of both theoretical and experimental studies of HER electrocatalysts with special emphasis on the electronic structure, surface (electro)chemistry, and molecular design. It addresses the importance of correlating theoretical calculations and electrochemical measurements toward better understanding of HER electrocatalysis at the atomic level. Fundamental concepts in the computational quantum chemistry and its relation to experimental electrochemistry are also presented along with some featured examples.

Advancing the Electrochemistry of the Hydrogen-Evolution Reaction through Combining Experiment and Theory

Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts. Insights into the rational design of single-atom metal catalysts remains obscure in heterogeneous catalysis. Here, the authors establish the atomic-level structure–activity relationship for a wide-pH-range hydrogen evolution reaction through the electronic metal–support interaction modulation.

/pdf/electronic-metal-support-interaction-modulates-single-atom-4bejbf95wz.pdf

Electronic metal-support interaction modulates single-atom platinum catalysis for hydrogen evolution reaction.

Platinum is a prominent catalyst for a multiplicity of reactions because of its high activity and stability. As Pt nanoparticles are normally used to maximize catalyst utilization and to minimize catalyst loading, it is important to rationalize and predict catalytic activity trends in nanoparticles in simple terms, while being able to compare these trends with those of extended surfaces. The trends in the adsorption energies of small oxygen- and hydrogen-containing adsorbates on Pt nanoparticles of various sizes and on extended surfaces were analyzed through DFT calculations by making use of the generalized coordination numbers of the surface sites. This simple and predictive descriptor links the geometric arrangement of a surface to its adsorption properties. It generates linear adsorption-energy trends, captures finite-size effects, and provides more accurate descriptions than d-band centers and usual coordination numbers. Unlike electronic-structure descriptors, which require knowledge of the densities of states, it is calculated manually. Finally, it was shown that an approximate equivalence exists between generalized coordination numbers and d-band centers.

Fast Prediction of Adsorption Properties for Platinum Nanocatalysts with Generalized Coordination Numbers

Exploring efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is critical for developing anion exchange membrane electrolyzers. The key to a rational catalyst design is understanding the descriptors that govern the alkaline HER activity. Unfortunately, the principles that govern the alkaline HER performance remain unclear and are still under debate. By studying the alkaline HER at a series of NiCu bimetallic surfaces, where the electronic structure is modulated by the ligand effect, we demonstrate that alkaline HER activity can be correlated with either the calculated or the experimental-measured d band center (an indicator of hydrogen binding energy) via a volcano-type relationship. Such correlation indicates the descriptor role of the d band center, and this hypothesis is further supported by the evidence that combining Ni and Cu produces a variety of adsorption sites, which possess near-optimal hydrogen binding energy. Our finding broadens the applicability of d band theory to activity prediction of metal electrocatalysts and may offer an insightful understanding of alkaline HER mechanism.

https://dr.ntu.edu.sg/bitstream/10356/148443/2/Chao%20Wei%20DR-NTU.pdf

Surface Composition Dependent Ligand Effect in Tuning the Activity of Nickel-Copper Bimetallic Electrocatalysts toward Hydrogen Evolution in Alkaline.

The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, He II, and monochromatized Al Kα excitation. The influence of final states, photoionization cross-section, and adsorption of residual gas molecules in an ultrahigh vacuum environment are discussed in terms of their impact on the VBS. We find that VBSs recorded with monochromatized Al Kα radiation are most closely comparable to the ground state density of states (DOS) derived from quantum mechanics calculations. We use the Al Kα-excited PES measurements to correct the energy scale of the calculated ground-state DOS to approximate the “true” ground-state d-band structure. Finally, we use this data to test the d-band center model commonly used to predict the electronic-property/catalytic-activity relationship of metals. We find that a simple continuous dependence of activity on d-band center position is not supported by our results (both experimentall...

/pdf/using-photoelectron-spectroscopy-and-quantum-mechanics-to-1hirrypw08.pdf

Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications

We wholeheartedly agree with the majority of statements
made in the comment-that an understanding of the
electronic structure of catalyst surfaces to understand their
catalytic activity is one of the most important subjects within
the field of catalysis research, that a simplified approach to
correlating electronic structure and activity would be desirable,
that our study testing, among other things, such a correlation is
therefore of “significant importance”, that, however, such a
simplified correlation is not at all straightforward, and hence an
oversimplified “d-band center model” is not really adequate to
describe the complicated processes involved in catalytic activity.
The comment also gives a nice example of final state effects in
photoemission spectra (a satellite structure 6 eV below the
Fermi energy of Fe, Co, and Ni), which obscure an
experimental determination of the ground state d-band center
(as described in our paper). Finally, the comment gives a good
summary of the bibliography of the comment’s authors in this
research field.

Reply to “Comment on ‘Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications’”

INTRODUCTION: Gun violence is a major public health problem in the US. Mass shooting events (MSE), defined as 4 or more shot and/or killed in a single event, have major effects on public opinion and policy surrounding guns. Previously, we determined that states with higher gun law grades did not have lower MSE incidence. How socioeconomic factors are associated with MSE incidence is not understood. The primary aim of this study was to identify county-level socioeconomic risk factors that are associated with MSE. METHODS: MSE data were obtained from the Gun Violence Archive for the years 2015 to 2019. Socioeconomic data were obtained from the 2019 US Census American Community Survey 5-year estimate data profiles. Socioeconomic factors for counties with and without MSE were compared using the Mann-Whitney U test and logistic regression. RESULTS: A total of 1,816 MSE occurred in 473 of 3,142 (15.1%) US counties in the years examined. There were 9,806 MSE victims, of whom 2,097 (21.4%) were fatally injured and 7,709 (78.6%) were nonfatally injured. The number of MSEs and fatally or nonfatally injured victims was highest in Cook County, IL. GINI index, educational attainment, and families with children were associated with MSE on multivariate analyses. Lower median income itself was not associated with an increased incidence of MSE (Table). Table 1. - Univariate and Multivariate Analysis of Relevant Socioeconomic Factors Characteristic No Mass Shooting Events Mass Shooting Events Odds Ratio (Univariate) Odds Ratio (Multivariate) GINI index 44.2 (3.6) 46.4 (3.3) 1.18 (1.14–1.21, p < 0.001) 1.11 (1.07–1.16, p < 0.001) Households with children 27.8 (4.2) 30.0 (3.3) 1.13 (1.10–1.16, p < 0.001) 1.09 (1.05–1.12, p < 0.001) Households where grandparents raise children 47.6 (18.3) 40.4 (12.3) 0.98 (0.97–0.98, p < 0.001) 0.99 (0.98–1.00, p = 0.015) Bachelor’s degree 13.7 (5.4) 16.9 (6.2) 1.09 (1.08–1.11, p < 0.001) 1.09 (1.06–1.12, p < 0.001) US citizenship 95.9 (4.8) 91.2 (8.3) 0.90 (0.89–0.91, p < 0.001) 0.93 (0.91–0.95, p < 0.001) Unemployment rate 5.2 (2.7) 6.0 (2.0) 1.11 (1.07–1.14, p < 0.001) 1.04 (0.99–1.11, p = 0.142) Below poverty level 10.7 (5.5) 11.8 (5.1) 1.04 (1.02–1.05, p < 0.001) 0.97 (0.93–1.01, p = 0.113) African American 7.1 (12.9) 20.4 (17.9) 1.05 (1.04–1.05, p < 0.001) 1.05 (1.04–1.06, p < 0.001) CONCLUSION: MSE occur in counties with identifiable socioeconomic risk factors. Interventions addressing various socioeconomic factors, especially income inequality, may decrease the incidence of MSE. 

Effect of Socioeconomic Factors on Mass Shooting Events: A 5-Year Analysis

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Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications

Reply to “Comment on ‘Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications’”

Effect of Socioeconomic Factors on Mass Shooting Events: A 5-Year Analysis