Transition-metal single atoms in nitrogen-doped graphenes as efficient active centers for water splitting: a theoretical study

• Published in: Physical chemistry chemical physics : PCCP Vol. 21; no. 6; pp. 3024 - 3032
• Main Authors: Zhou, Yanan, Gao, Guoping, Li, Yan, Chu, Wei, Wang, Lin-Wang
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 06.02.2019; Royal Society of Chemistry (RSC)
• Subjects: Catalysis; Catalytic activity; Cobalt; Continuum modeling; Coordination numbers; Copper; Density functional theory; Electrocatalysts; Free energy; Hydrogen evolution reactions; Hydrogen-based energy; Iron; Nickel; Nitrogen; Noble metals; Oxygen evolution reactions; Oxygen production; Palladium; Single atom catalysts; Transition metals; Water splitting
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/C8CP06755D

Highly active single-atom catalysts (SACs) have recently been intensively studied for their potential in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Due to the existence of many such SAC systems, a general understanding of the trend and designing principle is necessary to discover an optimal SAC system. In this work, by using density functional theory (DFT), we investigated a series of late single transition metals (TM = Fe, Co, Ni, Cu, and Pd) anchored on various N doped graphenes ( x N–TM, x = 1–4) as electrocatalysts for both the HER and OER. Solvent effects were taken into account using an implicit continuum model. Our results reveal that the catalytic activity of SACs is determined by the local coordination number of N and TM in the catalysts. Among the considered catalysts, a low-coordinated Co site, i.e. a triple-coordinated Co, exhibits a high catalytic activity toward the HER with a calculated hydrogen adsorption free energy of −0.01 eV, whereas a high-coordinated Co center, i.e. a quadruple-coordinated Co is a promising candidate for the OER with a low computed overpotential of −0.39 V, which are comparable to those of noble metal catalysts, indicating superior HER and OER performance of N–Co co-doped graphenes. The results shed light on the potential applications of TM and N co-doped graphenes as efficient single-atom bifunctional catalysts for water splitting, thereby functioning as promising candidates for hydrogen/oxygen production.