Nickel Cobalt Phosphite Nanorods Decorated with Carbon Nanotubes as Bifunctional Electrocatalysts in Alkaline Medium with a High Yield of Hydrogen Peroxide

Abstract

Abstract It is highly desirable to develop an energy generation system comprising a low‐cost and earth‐abundant non‐noble metal catalyst for bifunctional electrocatalysis with good overall process performance, especially for applications in fuel cells or metal‐air batteries. In this report, we show that nickel cobalt phosphite (NiCo−Phi) decorated with carbon nanotubes (CNTs) can perform as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions (OER and ORR, respectively). The NiCo−Phi/CNT composite is synthesized by employing a simple, single‐step hydrothermal method. The morphology of the composite consists of nanorod bundles of NiCo−Phi decorated with CNTs. The synthesized NiCo−Phi/CNT composite exhibits enhanced electrochemical OER activity with an overpotential of 400 mV at a current density of 10 mA/cm 2 and a Tafel slope value of 117 mV dec −1 in 1 M KOH, possessing high stability towards the OER for 20 h. The ORR using the same catalyst shows an onset potential of 0.75 V and a Tafel slope of 100 mV dec −1 in 0.1 M KOH with high‐yield production of H 2 O 2 (85 %). The predominant formation of H 2 O 2 occurs mainly through a two‐electron transfer process, as established by mass‐controlled kinetic studies and has not been observed previously in these phosphorous oxy anion‐based materials. The superior bifunctional nature of NiCo−Phi/CNT towards the OER and ORR arises from the synergistic effect of doped metal phosphites and CNTs.