Kinetically Constrained Capture and Conversion of CO ₂ from Ambient Air Using Excess Oxygen-Derived Recalcitrant Carbonates

The direct capture and methanation of CO2 from ambient air is traditionally conducted over dual-function materials containing at least two distinct elements─a CO2 binding site that facilitates concentration of CO2 at a gas–solid interface, and an active site that converts said adsorbed CO2 to methane through reaction with gas-phase hydrogen. We report herein the use of extralattice oxygen defects on unary and binary extended NiO surfaces to create a single-component dual-function material that, in its partially reduced form, effects both desired functions: adsorption and methanation. Specifically, we show how excess oxygen-derived recalcitrant carbonates─purportedly bidentate in configuration─can persist on oxide surfaces well into the methanation temperature range, and also be conferred the propensity for reactive desorption to form methane. Reactive desorption of these recalcitrant carbonates facilitates methanation at temperatures significantly lower than is typical for existing capture and methanation systems, and renders the CO2 concentration-reaction scheme to be limited by kinetic barriers associated with its activation, rather than its desorption. High-valent doping perturbs surface acid–base properties in a manner that concurrently destabilizes oxygen vacancies and stabilizes excess oxygens, enabling redressal of two principal challenges encumbering the design of capture and conversion materials, namely, cyclic stability and low-temperature methane productivity. Non-synthetic strategies for extralattice oxygen defect creation, including thermal treatments in inert streams, also help provide the requisite bidentate carbonate densities, suggesting transition-metal oxides as a tunable, noble-metal-free platform for the capture and conversion of CO2 from ambient air into value-added products such as methane. The data presented also reveal aliovalent dopant density, excess oxygen content, and carbonate denticity as readily accessible variables that enable amplification of the separations and catalysis performance of extended oxide surfaces.