NaBH 4 ‐induced phase transition of CoSe 2 with abundant Se deficiency for acidic oxygen reduction to hydrogen peroxide

Abstract Electrocatalytic oxygen reduction (ORR) via the 2e − pathway to form H 2 O 2 in acidic medium has attracted extensive attention. However, the low activity, insufficient selectivity and high cost of catalysts have been the bottlenecks. Herein, CoSe 2 with abundant Se deficiency was synthesized by a simple hydrothermal method, and the addition of NaBH 4 ‐induced CoSe 2 phase transition from orthorhombic to cubic phase with more Se deficiency. The cubic phase CoSe 2 with abundant Se deficiency can effectively regulate the surface electronic structure with suitable binding energies of *OOH and *O, which shows high activity, selectivity and long‐term stability for acidic ORR to H 2 O 2 . The onset potential is as low as 0.73 V vs. reversible hydrogen electrode (RHE), the H 2 O 2 selectivity is 84% (0 V vs. RHE), and the average electron transfer number is about 2.3. Furthermore, the H 2 O 2 yield measured using a flow cell is as high as 115.92 mmol·g cat. −1 ·h −1 and the Faradaic efficiency is 70% at 0 V vs. RHE, which presents high potential in electrocatalytic acidic ORR to H 2 O 2 and organic pollutant degradation using the electron‐Fenton process.