Zinc-Substituted Cobalt Phosphate [ZnCo2(PO4)(2)] as a Bifunctional Electrocatalyst

Zinc-substituted cobalt phosphateZnCo(2)(PO4)(2), synthesized using alow-cost, scalable solutioncombustion route having nanometric particles with high porosity, exhibitedefficient oxygen evolution and oxygen reduction (ORR and OER) activitiesin basic media of 0.1 M KOH. The companionship of distorted cobaltand zinc trigonal bipyramids on one of the interstitial sites allowsZnCo(2)(PO4)(2) to function as a robustbifunctional catalyst delivering electrocatalytic activity comparableto the state-of-the-art precious metal catalysts (Pt/C and RuO2). Development of highly efficient,earth-abundant, and stable bifunctionalelectrocatalysts is pivotal for designing viable next-generation metal-airbatteries. Cobalt-based phosphates provide a treasure house to designelectrocatalysts, with a wide range of cation substitutions to furtherenhance their electrocatalytic activity. In particular, phosphateswith distorted geometry show favorable binding efficiency toward watermolecules with low overpotential. In the present work, zinc-substitutedcobalt phosphate ZnCo2(PO4)(2) wasinvestigated. Its crystal structure was solved to a monoclinic frameworkbuilt with CoO6 octahedra and distorted CoO5/ZnO5 trigonal bipyramid leading to efficient bifunctionalelectrocatalytic activity. It offers robust structural stability withonset potential values of 0.87 V (vs reversible hydrogen electrode(RHE)) and 1.50 V (vs RHE) for oxygen reduction reaction (ORR) andoxygen evolution reaction (OER) processes, respectively, comparableto the precious metal catalysts. The origin and stability of the bifunctionalactivity were probed by combining ex situ diffraction and electronmicroscopy corroborated by ab initio calculations.Overall, zinc-substituted cobalt phosphate [ZnCo2(PO4)(2)] forms a potential bifunctional electrocatalystwith tunable local cobalt coordination that can be harnessed for metal-airbatteries.

Automated summary

ZnCo2(PO4)(2), a zinc-substituted cobalt phosphate synthesized using a low-cost solution combustion route, exhibited efficient oxygen evolution and reduction activities. The crystal structure of ZnCo2(PO4)(2) consists of distorted cobalt and zinc trigonal bipyramids, which allow it to function as a robust bifunctional catalyst comparable to precious metal catalysts. This research provides valuable insights for the development of highly efficient and stable electrocatalysts for metal-air batteries.