A hierarchical oxygen vacancy-rich WO₃ with "nanowire-array-on-nanosheet-array" structure for highly efficient oxygen evolution reaction

The search for highly efficient non-noble metal-based catalysts for the oxygen evolution reaction (OER) has received growing attention. Herein, we demonstrate a hierarchical oxygen vacancy-rich WO₃ with "nanowire array on nanosheet array" (WO₃ NWA-NSA) structure as a highly efficient catalyst for the OER. The vertical structure can not only highly improve the mass loading of WO₃ catalysts on Ni foam, but also provide efficient paths and channels for electron and mass transfer, leading to superior catalytic activity. Besides, the oxygen vacancies in WO₃ further promote the OER activity. The as-prepared WO₃ NWA-NSA catalyst requires an extremely low overpotential of 0.23 V to achieve a benchmark of 10 mA cm^-2, with a Tafel slope of only 33 mV dec^-1, superior to most reported state-of-the-art nonprecious metal-based catalysts and noble oxide catalysts. Further theoretical modeling calculations indicate that the electronic structure of WO₃ with oxygen vacancies fits extremely well with the requirements of OER catalysts. This facile strategy provides a new avenue toward the hierarchical design of electrocatalysts, and our research opens a brand-new field for the applications of WO₃.