Significance: The production of solar fuels from CO ₂ using sunlight and electricity provides one promising route for reducing atmospheric carbon emissions and storing intermittent solar energy. The rational design of an efficient and inexpensive electrocatalyst is the key. We developed a binary copper−iron catalyst for photoelectrochemical CO ₂ reduction toward methane. The theoretical calculations suggest that Cu and Fe in the binary system can work in synergy to spontaneously favor CO ₂ activation and conversion for methane synthesis. The earth-abundant CuFe catalyst exhibits a high current density with an impressive methane Faradaic efficiency using industry-ready planar silicon photoelectrodes under one-sun illumination. This work presents a unique, highly efficient, and inexpensive route for solar fuels synthesis.

Upcycling of CO₂ into fuels by virtually unlimited solar energy provides an ultimate solution for addressing the substantial challenges of energy crisis and climate change. In this work, we report an efficient nanostructured Ru/MnO_x catalyst composed of well-defined Ru/MnO/Mn₃O₄ for photo-thermal catalytic CO₂ hydrogenation to CH₄, which is the result of a combination of external heating and irradiation. Remarkably, under relatively mild conditions of 200 °C, a considerable CH₄ production rate of 166.7 mmol g⁻¹ h⁻¹ was achieved with a superior selectivity of 99.5% at CO₂ conversion of 66.8%. The correlative spectroscopic and theoretical investigations suggest that the yield of CH₄ is enhanced by coordinating photon energy with thermal energy to reduce the activation energy of reaction and promote formation of key intermediate COOH* species over the catalyst. This work opens up a new strategy for CO₂ hydrogenation toward CH₄.

A unique GaN:Sn nanoarchitecture is integrated on planar silicon to demonstrate an energetically favorable reaction path for aqueous photoelectrochemical CO₂ reduction towards formic acid with high efficiency at low overpotential.