Photoelectrochemical reduction of CO2 catalyzed by a 3D core–shell NiMoO4@ZnO heterojunction with bicentre at the (111) plane and thermal electron assistance

Abstract

The photoelectrochemical (PEC) reduction of CO₂ into organic chemicals on the semiconductor is considered a feasible plan to address the global energy crisis and climate warming. Herein, the heterojunctions NiMoO₄/ZnO-x are designed and synthesized. The nanosheets of NiMoO₄ have excellent absorption of photons and benefit the C–C coupling to C2 compounds. The ZnO/C core fabricated from MOF rich in CN species harvests light to generate a lot of thermal electrons assisting CO₂ reduction. Benefitting from its unique chemical properties and structure, the as-prepared NiMoO₄/ZnO-3 heterojunction exhibited impressive performance in CO₂ reduction, yielding oxygenated chemicals with 72.6% selectivity for C2 products at a rate of 29.2 μM cm⁻² h⁻¹. The formation rate under photoelectrochemical conduction is three times that of photocatalysis plus electrocatalysis, showing a strong synergetic effect of photo- and electro-catalysis. The isotopic labeling experiments of ¹³CO₂ verified that the products are derived from CO₂ and water. Finally, a new catalytic mechanism with bimetallic centers is proposed firstly to explain the reaction pathways with high selectivity of C2 chemicals. The important intermediates and the C–C coupling via Ni–Mo bicentre are proven by density-functional theory (DFT) calculations and verified by operando Fourier transform infrared (FTIR) spectrometry. On the other hand, the effect of thermal electrons is investigated as well.