Theoretical Study on Improving the CO2 Reduction Performance of the Cu2ZnGeS4 Photoelectrode via Doping and Surface Engineering

Cu2ZnGeS4 (CZGS) and Cu2ZnSnS4 (CZTS) represent an important kesterite-structure family of photovoltaic materials due to low cost and toxicity. The upshift of CZGS’s conduction band minimum (CBM) compared to that of CZTS has also drawn attention recently for a potential application of CZGS in a photo-electro CO2 reduction reaction (CO2RR), which is, however, limited by a relatively large band gap and a low selectivity of the system. In this study, we employ ab initio atomic-scale models to explore the possibility of adjusting the electronic structure and catalytic selectivity of the CZGS (112) facet via doping and surface engineering approaches. We demonstrate that the substitution of Cu with Fe or Cr dopants can significantly shift up the valence band maximum position without much influence on the CBM level, thus leading to a smaller band gap while maintaining the strong reduction driving force of CZGS. Moreover, we reveal that different surface terminations of the CZGS (112) facet exhibit different selectivities toward CO2RR against the hydrogen evolution reaction (HER). We propose two possible surface terminations that could thermodynamically suppress hydrogen adsorption, providing guidance for the experimental treatment of the CZGS photoelectrode surface applied for CO2RR.