For steady electroconversion to value-added chemical products with high efficiency, electrocatalyst reconstruction during electrochemical reactions is a critical issue in catalyst design strategies. Here, we report a reconstruction-immunized catalyst system in which Cu nanoparticles are protected by a quasi-graphitic C shell. This C shell epitaxially grew on Cu with quasi-graphitic bonding via a gas–solid reaction governed by the CO (g) - CO₂ (g) - C (s) equilibrium. The quasi-graphitic C shell-coated Cu was stable during the CO₂ reduction reaction and provided a platform for rational material design. C₂₊ product selectivity could be additionally improved by doping p-block elements. These elements modulated the electronic structure of the Cu surface and its binding properties, which can affect the intermediate binding and CO dimerization barrier. B-modified Cu attained a 68.1% Faradaic efficiency for C₂H₄ at −0.55 V (vs RHE) and a C₂H₄ cathodic power conversion efficiency of 44.0%. In the case of N-modified Cu, an improved C₂₊ selectivity of 82.3% at a partial current density of 329.2 mA/cm² was acquired. Quasi-graphitic C shells, which enable surface stabilization and inner element doping, can realize stable CO₂-to-C₂H₄ conversion over 180 h and allow practical application of electrocatalysts for renewable energy conversion.

Nanostructured Si eliminates several critical problems with Si photocathodes and dramatically improves a photoelectrochemical (PEC) reaction important to water-splitting. Our nanostructured black Si photocathodes improve the H₂ production by providing (1) near-ideal anti-reflection that enables the absorption of most incident light and its conversion to photogenerated electrons and (2) extremely high surface area in direct contact with water that reduces the overpotential needed for the PEC hydrogen half-reaction. Application of these advances would significantly improve the solar H₂ conversion efficiency of an ideal tandem PEC system. Finally, the nanostructured Si surface facilitates bubble evolution and therefore reduces the need for surfactants in the electrolyte.