Hydrothermal synthesis of high-performance cobalt phosphate nanorod architecture as bifunctional electrocatalysts for rechargeable Zn-air batteries and supercapatteries

Transition metal phosphate bifunctional electrocatalysts demonstrate superior oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and capacitive properties owing to their high electrocatalytic and conductive activities. In this report, cobalt phosphate (Co₃P₂O₈) nanorod (NR) electrocatalytic materials were developed via a facile one-step hydrothermal synthesis, followed by an annealing process. The unique NR structures offer superior electrocatalytic activities, continuous and quick electron transport pathways, short ion diffusion lengths, and rich active sites toward rechargeable zinc-air batteries (ZABs) and supercapatteries (SCs). The self-assembled Co₃P₂O₈ NR electrocatalyst revealed higher current density values during the OER and ORR measurements than the commercially available Pt/C and IrO₂ materials. The Co₃P₂O₈ NR electrocatalyst exhibited an excellent OER overpotential of 180 mV. The electocatalyst also showed superior onset and half-wave potentials of 0.92 V and 0.80 V, respectively. Moreover, the fabricated Co₃P₂O₈ NRs-based ZAB exhibited better durability than the Pt/C-based ZAB. Significantly, the Co₃P₂O₈ NR electrode demonstrated an excellent specific capacity of 373 mAh g⁻¹ with outstanding cycling stability of 99% after 5000 cycles. Additionally, the fabricated Co₃P₂O₈ NRs//activated carbon SC demonstrated high specific energy and power densities of 25.62 Wh kg⁻¹ and 2953.12 W kg⁻¹, respectively with remarkable cycling stability of 89% after 7000 cycles. Specifically, the practical applicability of the fabricated Co₃P₂O₈ NRs-based ZAB and SC was tested using a blue light-emitting diode nameplate energized by two devices in series. Overall, the catalytic and energy-storage properties of the Co₃P₂O₈ NR material can provide a new pathway for high-energy electrochemical applications.