Cow Dung Derived PdNPs@WO3 Porous Carbon Nanodiscs as Trifunctional Catalysts for Design of Zinc-Air Batteries and Overall Water Splitting

The main motif of this work is to fabricate a highly efficient, economic, nanodisc shaped trifunctional electrocatalyst using a tungsten trioxide modified carbon nanosheet decorated with palladium nanoparticles. The beauty of this work is that a special carbon precursor is used for the synthesis of the electrocatalyst, a waste material, i.e., cow dung. The performance of the cow dung derived nanodisc electrocatalyst (Pd@WO3-NDs) toward oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) is compared with three other electrocatalysts (derived from graphene oxide, chitosan, and graphite carbon sources) also, and it is found that Pd@WO3-NDs show superior performance over that of the other three. The electrocatalyst exhibits the lowest onset potential (1.32 V vs NHEs), highest current density (492 mA cm(2)), lowest overpotential (113 mV), and lowest Tafel slope (62.8 mV dec(1)) for OER; an onset potential of 1.02 V, overpotential of 195.0 mV, and Tafel slope of 53.1 mV dec(1)) for ORR; and lowest onset potential (-0.09 V), overpotential (185 mV at 10 mA cm(2)), and a small Tafel slope of (58.2 mV dec1) for HER in the same alkaline solution. In addition, the nanomaterial is successfully applied for the fabrication of rechargeable and all-solid-state zincair batteries, which are used to illuminate a 4.0 V light emitting diode (LED) bulb. More importantly, real air cathodes made from the trifunctional Pd@WO3-NDs demonstrated superior performance to state-of-the-art Pt/C catalysts in rechargeable zincair batteries. In addition, the same Znair battery is further used to power the laboratory-made total alkaline water electrolyzer by employing Pd@WO3-NDs as catalyst on both anode and cathode. The water electrolyzer showed comparable performance rivalling the state-of-art combination of Pt/C and RuO2, which is known to be the best of the bifunctional total-water splitting electrocatalysts reported until date. This remarkable performance of Pd@WO3-NDs indicates their future potential in energy storage and sustainable energy conversion technologies.