Lattice Strain-Modulated Trifunctional CoMoO4 Polymorph-Based Electrodes for Asymmetric Supercapacitors and Self-Powered Water Splitting

Developing efficient, multifunctional electrodes for energy storage and conversion devices is crucial. Herein, lattice strains are reported in the β-phase polymorph of CoMoO₄ within CoMoO₄@Co₃O₄ heterostructure via phosphorus doping (P-CoMoO₄@Co₃O₄) and used as a high-performance trifunctional electrode for supercapacitors (SCs), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) in alkaline electrolytes. A tensile strain of +2.42% on the β-phase of CoMoO₄ in P-CoMoO₄@Co₃O₄ results in superior electrochemical performance compared to CoMoO₄@Co₃O₄. The optimized P-CoMoO₄@Co₃O₄ achieves a high energy density of 118 Wh kg⁻¹ in an asymmetric supercapacitor and low overpotentials of 189 mV for the HER and 365 mV for the OER at a current density of 500 mA cm⁻². This results in a low overall water splitting voltage of 1.71 V at the same current density making it an effective bifunctional electrode in a 1 m KOH freshwater electrolyte. Theoretical analysis shows that the excellent performance of P-CoMoO₄@Co₃O₄ can be attributed to interfacial interactions between CoMoO₄ and Co₃O₄, and the β-phase of CoMoO₄, which lead to strong OH⁻ adsorption and low energy barriers for reaction intermediates. Practical application is demonstrated by using P-CoMoO₄@Co₃O₄-based ASCs to self-generate hydrogen (H₂) in a P-CoMoO₄@Co₃O₄||P-CoMoO₄@Co₃O₄ alkaline seawater electrolyzer, showcasing its potential for future energy technologies.