A Comprehensive Pyrolysis Mechanism of Binuclear Chromium-Based Complexes for Superior OER Activity
Meixing Gan, Li Li, Xixian Yang, Hongwei Rong, Zheng Wang, Yuebin Li, Yuexing Zhang, Xueli Chen, Peng Xu
Abstract
Transition metal oxides are widely pursued as potent electrocatalysts for the oxygen evolution reaction (OER). However, single-metal chromium catalysts remain underexplored due to their intrinsic activity limitations. Herein, we successfully synthesize mixed-valence, nitrogen-doped Cr 2 O 3 /CrO 3 /CrN@NC nanoelectrocatalysts via one-step targeted pyrolysis techniques from a binuclear Cr-based complex (Cr 2 (Salophen) 2 (CH 3 OH) 2 ), which is strategically designed as a precursor. Comprehensive pyrolysis mechanisms were thoroughly delineated by using coupled thermogravimetric analysis and mass spectrometry (TG–MS) alongside X-ray diffraction. Below 800 °C, the generation of a reducing atmosphere was noted, while continuous pyrolysis at temperatures exceeding 800 °C promoted highly oxidized CrO 3 species with an elevated +6 oxidation state. The optimized catalyst pyrolyzed at 1000 °C (Cr 2 O 3 /CrO 3 /CrN@NCs-1000) demonstrated remarkable OER activity with a low overpotential of 290 mV in 1 M KOH and excellent stability. Further density functional theory (DFT) calculations revealed a much smaller reaction energy barrier of CrO 3 than the low oxidation state species for OER reactivity. This work reveals fresh strategies for rationally engineering chromium-based electrocatalysts and overcoming intrinsic roadblocks to enable efficient OER catalysis through a deliberate oxidation state and compositional tuning.