Constructing a Stable 2D/2D Heterojunction of Oxygen-Cluster-Modified Ti3AlC2 MAX Cocatalyst with Proton-Rich C3N4 for Highly Efficient Photocatalytic CO2 Methanation

A novel two-dimensional (2D)/2D heterostructure of oxygen-defective OV-Ti 3 AlC 2 MAX with proton-rich functionalized carbon nitride (f-C 3 N 4 ) was fabricated for photocatalytic CO 2 conversion into energy-rich solar fuels, CH 4, in the presence of H 2 O/H 2 under visible light. During CO 2 photoreduction with H 2 O over f-C 3 N 4, CO was produced rapidly; however, incorporating OV-Ti 3 AlC 2, selective CH 4 evolution was observed. The CH 4 yield rate up to 786 μmol g cat –1 h –1 was achieved via photodriven CO 2 hydrogenation over the composite catalyst, which are 13- and 15-fold higher than Ti 3 AlC 2 and graphitic carbon nitride (g-C 3 N 4 ) catalysts, respectively. This superior performance confirms the higher electrical conductivity and efficient interfacial charge transfer due to dual mediators with oxygen clusters. Thermodynamic analysis reveals that both CO and H 2 intermediates greatly contribute to boosting CH 4 generation, while the highest energy is consumed during water splitting. In other words, H 2 is necessary for CO 2 hydrogenation, which can be injected directly or can be produced by water splitting. The optimized H 2 /CO 2 feed ratio of 2.0 further confirmed the adsorption competition of reactants before converting to CH 4. Cyclic experiments show the highest catalytic reactivity with durability for continuous CH 4 production without obvious deactivation. With the OV-Ti 3 AlC 2 MAX framework structure, significant opportunities exist in terms of improved catalyst reactivity for single-step CO 2 methanation to solar fuels.