Strategies for computational design and discovery of two-dimensional transition-metal-free materials for electro-catalysis applications

Significance of density functional theory (DFT) calculations for electrocatalysis of N2 and CO2 reduction reactions

Density functional theory (DFT) based computational methods have shown great significance in developing high-performance electrocatalysts. In this perspective, we briefly summarized the state-of-the-art research progress of electrocatalysts for the nitrogen reduction reaction (NRR) and CO₂ reduction reaction (CO₂RR), which are important processes for the conversion of common molecules into value-added products. With the help of DFT calculations, various modulation strategies are employed to improve the catalytic activity and performance of NRR and CO₂RR electrocatalysts. DFT calculations are performed to confirm the surface catalytic sites, evaluate the catalytic activity, reveal the possible reaction mechanisms, and design novel structures with high catalytic performance. By discussing the currently applied computational methods and conditions during the calculations, we outlined our concerns on the prospects and future challenges of DFT calculations in electrocatalysis studies.

Mechanism of Oxygen Reduction Reaction in Alkaline Medium on Nitrogen-Doped Graphyne and Graphdiyne Families: A First Principles Study

Using extensive first principles protocols, a systematic investigation is performed to probe the oxygen reduction reaction (ORR) mechanism on nitrogen (N) doped graphynes (Gys, e. g. αGy, βGy, γGy and 6,6,12Gy) and graphdiyne (Gdy) in alkaline medium. We considered both associative and dissociative pathways, as well as two distinct intermediate forks for each of them depending on the first protonation site(s). Following the dissociative approach, the activation energy to form an O₂ dissociated configuration is found as a function of the distances migrated by the O atoms over the catalyst surface and the amount of charge transferred from the C atoms linked to N. N doped αGy and 6,6,12Gy emerged as the best electrocatalyst comparing both pathways having lowest overpotentials of 0.88 and 0.82 V, respectively. The rate-limiting steps for the two different intermediate routes are observed to be dependent on the first protonation site(s) and related to the desorption of the OH radical from the sp hybridized C atom site(s) linked to N. Hence, the OH adsorption energy is identified as a descriptor for the efficiency of the ORR for the considered systems. The stabilities of the ORR intermediates are further elaborated in terms of pH and electrode potential.

Density functional theory study of transition metal single-atoms anchored on graphyne as efficient electrocatalysts for the nitrogen reduction reaction

Ammonia (NH3) is the main raw material for the organic chemical industry and a critical feedstock for the fertilizer industry with great significance for the global economy. The NH3 demand has gradually increased with modern society development. Moreover, the electrocatalytic nitrogen reduction reaction (NRR) is a promising NH3 synthesis technology. However, the design of efficient electrocatalysts for the NRR is still challenging. In this study, we systematically analyzed transition metal (TM) single-atoms (Ti, V, Cr, Mn, Zr, Nb, and Mo) anchored on graphyne (GY) as NRR catalysts using density functional theory calculations. The calculation results for the first and last hydrogenation steps (*NNH formation and *NH3 desorption, respectively) revealed that Mn@GY (with an end-on configuration) and V@GY (with a side-on configuration) were the most suitable catalytic substrates for the NRR. The free-energy profiles of the TM@GY catalysts indicated that Mn@GY was the best NRR electrocatalyst owing to its distal pathway with a minimum free-energy barrier of 0.36 eV. In addition, the electronic properties, namely the Bader charge, charge density difference, partial density of states, and crystal orbital Hamilton population, of the TM@GY catalysts were analyzed in detail, and the results further confirmed that Mn@GY was an efficient electrocatalyst. The insights obtained from this comprehensive study can provide useful guidelines for designing new and efficient electrocatalysts.

Earth-Abundant Electrocatalysts for Water Splitting: Current and Future Directions

Of all the available resources given to mankind, the sunlight is perhaps the most abundant renewable energy resource, providing more than enough energy on earth to satisfy all the needs of humanity for several hundred years. Therefore, it is transient and sporadic that poses issues with how the energy can be harvested and processed when the sun does not shine. Scientists assume that electro/photoelectrochemical devices used for water splitting into hydrogen and oxygen may have one solution to solve this hindrance. Water electrolysis-generated hydrogen is an optimal energy carrier to store these forms of energy on scalable levels because the energy density is high, and no air pollution or toxic gas is released into the environment after combustion. However, in order to adopt these devices for readily use, they have to be low-cost for manufacturing and operation. It is thus crucial to develop electrocatalysts for water splitting based on low-cost and land-rich elements. In this review, I will summarize current advances in the synthesis of low-cost earth-abundant electrocatalysts for overall water splitting, with a particular focus on how to be linked with photoelectrocatalytic water splitting devices. The major obstacles that persist in designing these devices. The potential future developments in the production of efficient electrocatalysts for water electrolysis are also described.