First-Principles Calculation for Surface Chemistry of Electrocatalysts

Abstract

The demands for energy get increased due to the sharp increment of population. As hydrocarbon resources are mainly used as energy sources, the world faces a climate crisis due to CO2 emissions from these resources. In this regard, the development of a sustainable energy system is required. As a consequence, the hydrogen (H2) which can produce clean electricity gets a huge attraction. The H2 can be produced efficiently through electrocatalytic water splitting. The commercial electrocatalysts used in water splitting reaction has a problem with their price. This disadvantage of the price of H2 limits their production. Besides the electrocatalysts in water splitting, in fuel cell which makes electricity from H2, sluggish oxygen evolution/reduction reaction is another hindrance for their application. To overcome these problems, low-cost high-performance electrocatalysts should be developed. First-principles calculations using density functional theory (DFT) has been used to predict and understand the intrinsic activity of electrocatalyst. The adsorption energies of reaction intermediates produced during the elementary steps of electrocatalysis determine the activity of the electrocatalyst. The electronic states of the surface on which the intermediates are adsorbed determine the adsorption energies. By controlling the electronic states based on the surface chemistry like d-band center theory and surface coordination chemistry, the adsorption energies of intermediates can be optimized and higher activity can be achieved ultimately. In Chapter 2, we show high-throughput computational screening for high-performing 3d–5d transition metal (TM) single atoms (SAs) catalysts using DFT calculations. We explore tuning the stability and activity of TM on defect sites of nitrogen-doped graphene (TM–GN) in view of structure/coordination, formation energy, structural/electrochemical stability, electrical conductivity, and reaction mechanism. Among various –NxCy motifs in GN, the –N2C2 motifs tend to be more easily formed and have higher electrochemical catalytic performance (particularly in HER/OER) and longer durability (without aggregation into clusters and without dissolution) compared with widely studied pure –C4/C3 and –N4/N3 motifs. The TM(SA)s showing super-performances in HER/OER/ORR over benchmark noble metal nanoparticles (NPs) catalysts are assessed. In Chapter 3, we developed the high-performance electrocatalyst for OER using the inductive effect. Our calculation and experimental results revealed that the positive shift of redox potential of material by the inductive effect of phosphate and transition metals improves activity for OER. The Fe3Co(PO4)4 is predicted to be the most active for OER among various compositions theoretically. Then, the performance of electrocatalysis is tested and shows a very low overpotential of 237 mV at a high current density of 100 mA∙cm‒2 and outstanding stabilities. The synthesized materials are also characterized by XRD and EXAFS which are obtained experimentally and theoretically.