Directional oxygen activation by oxygen-vacancy-rich WO2 nanorods for superb hydrogen evolution via formaldehyde reforming

Abstract

Molecular oxygen activation (MOA) into reactive oxygen species (ROS) is extremely crucial in numerous catalytic processes, while precise control of ROS products remains difficult. Herein, we find that oxygen substoichiometric tungsten dioxide nanorods (WO₂ NRs) are an appropriate alternative to realize highly efficient O₂ promoted HCHO reforming to produce H₂. Rich oxygen vacancies (OVs) in WO₂ NRs play a fundamental role in the MOA induced catalytic H₂ evolution reaction because they guarantee the favorable chemisorption of molecular O₂ on the catalyst surface as well as build up a channel for the delivery of electrons to O₂ species. Importantly, MOA initiated by the WO₂ NR catalyst can be achieved by systematically modulating the proton-coupled electron transfer (PCET) pathway to controllably obtain the desired ROS and thus to directionally produce H₂, in which molecular O₂ receives the electrons to form superoxide radicals in a chemisorbed state (O₂˙⁻) and couple with protons provided by HCHO to convert into ·OOH radicals, rather than ·OH or other ROS. The surface stabilized HOO·–WO₂ NR complex acts as the catalytically active center in the dehydrogenation reaction. As O₂ continuously takes up and releases protons by formation and consumption of ·OOH radicals, O₂ persistently circulates on the WO₂ NR surface, making WO₂ NRs an unconventional catalyst. This study develops a new technique for clean energy supply and deepens our understanding of the MOA process during heterogeneous catalysis.