Light-Enhanced Thermochemical Production of Solar Fuels from Methane via Nickel-Based Redox Cycle

Thermochemical methane reforming driven by solar energy is one of the efficient ways to store the renewable energy and to simultaneously reduce greenhouse gas emission. We report reaction reactivity of steam reforming of methane using nickel-based oxygen carrier driven by pure thermal heating and direct light irradiation in the same reactor. We find that the light-driven steam methane reforming system show improved conversion and reaction rate compared to that driven by pure thermal heating. We observed that illuminated NiO/NiAl₂O₄ achieved the same methane conversion rates and the H₂ production rate comparable to those obtained on the same samples operated with only a thermal energy input, but at temperatures up to ~50 K lower. Based on <i>in situ</i> diffuse reflectance Infrared Fourier transform spectroscopy (DRIFTs) experiments, we postulate that light on the nickel oxide surface act to activate CH₄ desorption and facilitate CHxO species evolution. By the combined effects of selection of chemical looping reactions and operation conditions, the solar-to-fuel efficiency of 16% was achieved. The results showcase the design of more energy-efficient chemical processes with a significant fraction of energy input provided in the form of direct sunlight irradiation as a potent pathway that can complement extremely high-temperature thermochemistry efforts in the quest for more efficient solar fuel production.