High density facet junctions in nano-stepped CuFeO2 enable efficient charge separation for selective photocatalytic CO2 reduction to CH4

Facet junctions have been demonstrated to be effective in promoting the separation of photoinduced charges. However, the micro-size of photocatalysts with a limited density of facet junctions usually hinders the improvement of photocatalytic performance. In this work, we propose the synthesis of nanoscale CuFeO₂ through a hydrothermal and acid etching strategy, which leads to the formation of stepped CuFeO₂ hexagonal nanosheets with high-density facet junctions. Experimental characterization and density functional theory (DFT) calculations indicate that the steps are composed of horizontal (001) and vertical (−120) facets that form facet junctions, between which a work function difference of 0.74 eV induces the formation of a built-in electric field. Surface photovoltage measurements further demonstrate directional photoinduced electron transfer from (−120) to (001) to generate an electron-rich surface in CuFeO₂. As a result, the stepped CuFeO₂ with high-density facet junctions exhibits superior photocatalytic performance in the reduction of CO₂ to CH₄ compared to non-stepped CuFeO₂, with a rate of 43.79 μmol g⁻¹ h⁻¹ and 78% selectivity. In situ infrared spectroscopy further reveals that the stepped CuFeO₂ with a high density of facet junctions is more conducive to the formation of key CH₃O* intermediates that promote CH₄ production.