Efficient hydrogen production via sunlight-driven thermal formic acid decomposition over a porous film of molybdenum carbide

Abstract

Discovering efficient and low CO selectivity non-noble heterogeneous catalysts toward formic acid (FA) dehydrogenation is vital for H₂ energy systems. As a heating temperature is required to activate this reaction, the strategy of coupling a FA dehydrogenation reactor with a photothermal system possesses great potential for industrial applications. Herein, a sophisticated catalyst, a Mo_1.98C_1.02 porous film supported on carbon fiber paper, is demonstrated, with the advantages of a porous nanostructure, small nanoparticles and a carbon-supported structure simultaneously. The composite exhibits prominent thermal catalytic FA dehydrogenation, with a CO-free H₂ generation rate of 0.79 L g⁻¹ h⁻¹ at 100 °C. Density functional theory calculations show that the formate route (*OCHOH → *OCOH + 1/2H₂ → *OCO + 1/2H₂ → CO₂) is the minimum energy path for H₂ and CO₂ formation. Besides, a photothermal device was designed based on Bi₂Te₃/Cu, which can absorb and convert 1 kW m⁻² irradiation into a high temperature of 240 °C, due to the high sunlight absorption, low heat conduction and low heat irradiation. Thus, a sunlight-driven thermal catalytic system was designed based on this device, with a H₂ generation rate of 1.07 L g⁻¹ h⁻¹ under 0.25 kW m⁻². This value is about two orders of magnitude faster than that of photocatalytic FA decomposition over reported non-precious photocatalysts. These results demonstrate that FA dehydrogenation can be realized under weak solar irradiation with the assistance of photothermal systems, facilitating industrial applications.