Minimized TiO₂ Loading Improves the Plasmonic Cu Hot Carrier-Driven Methanol Steam Reforming Under Standard Solar Irradiation

Methanol is a promising liquid organic hydrogen carrier, and developing an efficient method to reform and release hydrogen from it with low thermal input is desirable. This study investigates plasmonic Cu nanoparticles derived from CuAl-LDH for thermo-photo catalytic (TPC) methanol steam reforming (MSR). The reduced catalyst (R-Cu/Al₂O₃) absorbs solar light up to 780 nm. Under standard irradiation (1.0 sun, AM1.5G) at 200 °C, the TPC hydrogen production rate via MSR (36.9 mmol·g^-1·h^-1) was four times higher than that achieved by the thermocatalytic (TC) process (9.0 mmol g^-1·h^-1). Notably, modifying R-Cu/Al₂O₃ with 1.0 wt % TiO₂ via a facile physical mixing method further boosted the TPC hydrogen production by 77%, reaching 65.2 (163.1) mmol·g^-1·h^-1 (mmol·g^-1·h^-1·W^-1). A strong correlation between the rate of hydrogen production and light absorption spectrum of plasmonic Cu was observed with a linear dependence on light intensity, confirming the role of hot-carriers in MSR reactions. Consequently, the apparent activation energy of PTC-MSR was reduced to 29.20 kJ·mol^-1, significantly lower than that of TC-MSR (62.15 kJ·mol^-1), thereby enhancing the kinetics of the TPC-MSR process. Complete MSR was achieved with a H₂-to-CO₂ ratio of three, with no CO detected, demonstrating its industrial viability.