Unlocking the activity of lattice oxygen in P-engineered MoO2 for efficient oxygen evolution reaction: a d-band center modulation perspective

Abstract

Activating lattice oxygen in oxygen evolution reactions (OER) serves as an effective strategy to overcome the inherent limitations of the traditional adsorbate evolution mechanism (AEM). Molybdenum dioxide (MoO₂), which has attracted attention due to its high electrical conductivity and other metallic properties, exhibits excessive adsorption of oxygen-containing intermediates at its elevated molybdenum d-band center. This leads to the formation of stable Mo–O bonds, thereby hindering the lattice oxygen mechanism (LOM). This study demonstrates that phosphorus doping serves as a more direct strategy for intrinsic electronic structure modulation. DFT calculations predict that phosphorus doping effectively lowers the d-band center of molybdenum and softens Mo–O bonds, thereby enabling lattice oxygen participation in the reaction mechanism. Consistent with the computational results, experimental kinetic studies (e.g., pH-dependent experiments) and chemical probe tests confirm that P-MoO₂ follows the LOM pathway. The prepared P-MoO₂ catalyst exhibits an overpotential of only 247 mV at 10 mA cm⁻² current density while maintaining stability for up to 100 hours. Furthermore, through various characterization techniques (TEM, XPS, in situ Raman spectroscopy), it was observed that the catalyst underwent significant potential-induced surface reconstruction during the reaction process, forming an amorphous MoO(OH)_x layer rich in Mo⁵⁺. This reconstructed layer is considered the true active phase, where Mo⁵⁺ has been confirmed as the dominant valence state in the OER process.