Cr Doping in Spinel Oxides Coordinates Adsorbate Evolution and Lattice Oxygen Pathways for Efficient Water Oxidation

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Sustainable hydrogen production via water electrolysis is crucial for clean energy.
• The oxygen evolution reaction (OER) kinetics are slow, requiring high overpotentials, hindering cost-effective electrolysis.
• Spinel oxides are promising electrocatalysts, but further optimization is needed.

Purpose of the Study:

• To synthesize and characterize novel 3d transition metal spinel oxides for enhanced OER.
• To investigate the role of chromium (Cr) doping in improving electrocatalytic performance.
• To explore synergistic effects between metal sites and lattice oxygen redox pairs.

Main Methods:

• Synthesis of multicomponent spinel oxide electrocatalysts using a Prussian blue analogue-mediated thermal decomposition method.
• Characterization of electronic structure and catalytic properties.
• Electrochemical evaluation of OER activity and stability.

Main Results:

• Chromium doping optimizes electronic structure and lowers energy barriers for the rate-determining steps in OER.
• The optimal catalyst, (Ni_0.6Co_0.5Fe_1.3Cr_0.6)O₄, exhibits an ultralow overpotential of 243 mV at 10 mA cm^-2.
• Exceptional operational stability exceeding 210 hours was achieved, outperforming existing spinel oxides.

Conclusions:

• Strategic d-block element engineering, specifically Cr doping, can orchestrate complementary OER mechanisms.
• This approach enables coupled electronic-lattice modulations, significantly enhancing catalytic efficiency.
• The developed spinel oxide demonstrates high potential for anion exchange membrane water electrolyzers.