Phosphorous-containing oxygen-deficient cobalt molybdate as an advanced electrode material for supercapacitors

The intrinsically poor electrical conductivity and insufficient number of electrochemically active sites of transition-metal oxides hamper their wide application in high-performance supercapacitors. Herein, we demonstrate an effective strategy of creating phosphorus-containing cobalt molybdate (CoMoO₄) with oxygen vacancies (P-CoMoO_4-x) on nickel foam for use as a supercapacitor electrode. Experimental analyses and theoretical calculations reveal that the electronic structure of P-CoMoO_4-x can be efficiently modulated by incorporating P heteroatoms and O vacancies, thereby simultaneously reducing the energy band gap and increasing electrical conductivity. Moreover, incorporating P into P-CoMoO_4-x weakens the Co–O bond energy and induces the low oxidation states of molybdenum species, facilitating surface redox chemistry and improving electrochemical performance. Accordingly, the optimized P-CoMoO_4-x electrode exhibits a high specific capacity of 1368 C g⁻¹ at a current density of 2 A g⁻¹, and it retains 95.3% of the initial capacity after 5000 cycles at a high current density of 10 A g⁻¹. An asymmetric supercapacitor assembled with the optimized P-CoMoO_4-x as positive electrode and activated carbon as negative electrode delivers a high energy density of 58 W h kg⁻¹ at a power density of 850 W kg⁻¹ as well as achieves excellent cycling lifespan.