CoP/Co2P@NC/MWCNTs as oxygen catalysts in alkaline seawater-based zinc-air batteries

Due to the serious problems of energy shortage and environmental pollution, seawater-based zinc-air (S-ZABs) batteries with low cost and reduced freshwater competition are considered to be a highly promising application for energy storage and energy conversion devices. However, the oxygen catalysts used in S-ZABs often suffer from Cl − poisoning and serious side reactions (ClER). Therefore, we synthesized multi-walled carbon nanotubes-supported nitrogen-doped carbon-coated CoP/Co 2 P nanoparticles (CoP/Co 2 P@NC/MWCNTs). The contents of P can be modulated by the ratio of Co(NO 3 ) 2 ·6H 2 O and NaH 2 PO 2 . The optimized CoP/Co 2 P-6@NC/MWCNTs with 1.4 % P, 20.88 % Pyridine-N exhibited excellent ORR activity (E 1/2  = 0.88 V, E onset  = 0.98 V, and J L  = 5.04 mA cm −2 ) in O 2 -saturated 0.1 mol L −1 KOH + 0.5 mol L −1 NaCl. CoP/Co 2 P-6@NC/MWCNTs exhibited excellent OER activity (E overpotential  = 299 mV at 10 mA cm −2 with the Tafel slope of 80.99 mV dec −1 ). The specific capacity of the Zn || CoP/Co 2 P-6@NC/MWCNTs seawater-based cell was as high as 805.26 mAh g −1 at a current density of 10 mA cm −2 . In addition, the Zn || CoP/Co 2 P-6@NC/MWCNTs seawater-based cell had an ultra-long cycling stability of more than 500 h, which demonstrated that CoP/Co 2 P-6@NC/MWCNTs has great potential to be as a seawater-based zinc-air cathode. This study opens a new way to design and synthesize non-precious metal OER/ORR bifunctional electrocatalysts in seawater electrolytes.