Ni/Hydrochar Nanostructures Derived from Biomass as Catalysts for H-2 Production through Aqueous-Phase Reforming of Methanol

Abstract

Aqueous-phase reforming of organic molecules to hydrogen is a promising strategy to address the production and storage of sustainable hydrogen with lower costs; however, the synthesis of inexpensive transition metal (TM) catalysts with desirable activity and stability for the reaction is still challenging. In this work, a green and efficient approach for modulating the geometric/electronic structure of metal/hydrochar nanocomposites from sustainable biomass was proposed for enhancing H-2 production via aqueous-phase reforming of methanol (APRM). A Ni/HC nanocomposite with a special thistle (a perennial species of flowering plant)-like three-dimensional (3D) architecture was first constructed as a model catalyst to expatiate the critical role of modulating an ordered mesoporous structure and interface electron transfer for enhancing APRM. Deliberately balancing heteroatom doping and soft templates contribute to the successful fabrication of the thistle-like superstructure, and such hierarchically porous architectures demonstrated efficient catalysis for APRM, owing to their unique properties, including a highly uniform morphology, narrow partide size distribution, and mesoporous texture with excellent accessibility. In addition, the experimental investigation and density functional theory calculations both substantiated that the combination of heteroatom doping and soft templates was beneficial for the strong electronic metal-support interaction (EMSI) of the metal/hydrochar nanocomposite, which leads to enhanced methanol adsorption, activation, and subsequently improved APRM performance. The electronic structure of the metal/hydrochar nanocomposite played a more significant effect on the intrinsic APRM activity than the geometric structure like the formation of the thistle-like superstructure. Benefiting from the tailored electronic and geometric structure, the resulting Ni-0.1/HC-N-1.5-S-1 catalyst exhibited an unprecedented average turnover frequency (TOF) of 89.5 mol(H2)/mol(Ni)/min, higher than any other known platinum group metal-free catalysts, approaching the reactivity of the state-of-the-art noble metal-based APRM catalysts, while showing excellent stability over 10 consecutive reaction cycles.