Invigorating the Catalytic Activity of Cobalt Selenide via Structural Phase Transition Engineering for Lithium–Oxygen Batteries

For the purpose of reducing kinetic obstacles of the oxygen evolution reaction and oxygen reduction reaction in rechargeable lithium–oxygen (Li–O₂) batteries, there is an urgent need for cost-effective and durable high-efficiency electrocatalysts. Descriptors of catalytic activity, local coordination environments, and electronic structures of transition-metal dichalcogenides can be modulated via phase transition engineering. Here, we report the strategy to induce transition of CoSe₂ from the cubic phase to the orthorhombic phase via phosphorus doping. The weak electronegativity of phosphorus as compared to selenium is beneficial for adjusting the amount of d electrons on the Co cation and thus has a significant contribution to structural phase transition and the electrocatalytic activity. As a result, the Li–O₂ battery with the phosphorus-doped orthogonal phase CoSe₂ (o-CoSe₂|P) electrode exhibits excellent rate capability (with a low overpotential of only 0.44 V at the current density of 50 mA g^–1) and cyclability (500 cycles). These experimental results prove that phase transition engineering is an effective strategy for obtaining highly efficient catalysts.