Comprehensive investigation of methane conversion over Ni(111) surface under a consistent DFT framework: Implications for anti-coking of SOFC anodes

Coking on nickel-based anodes is a key issue to be addressed for solid oxide fuel cell (SOFC) when using hydrocarbon fuels. In this work, the methane conversion process over Ni(111) surface has been systematically investigated under a consistent density functional theory (DFT) framework, aiming to seek efficient approaches to anti-coking. Following the conversion path of carbon-containing intermediates, a three-staged methane conversion pathway is derived over Ni(111) surface. The overall preferred route firstly follows the methane cracking path on Ni(111) surface from CH4 to CH (CH4 -> CH3 -> CH2 -> CH), then follows the CH conversion into CO through the CHOH formation path (CH -> CHOH -> CHO -> CO) and the CHO formation path (CH -> CHO -> CO), and final follows the CO oxidation into CO2 through the direct oxidation path (CO -> CO2) and the trans-COOH formation path (CO -> cis-COOH -> trans-COOH -> CO2). CHOH, CHO and trans-COOH are found to be the most important carbon-containing intermediates, while OH and O are found to be the key decoking media. Based on our DFT calculations, several feasible strategies to anti-coking on SOFC anodes are proposed and many experimental results in literatures are well explained. It is expected that the theoretical findings in the present study could provide some fundamental information to future research on carbon reduction on SOFC anodes.