Insights Into the Effect of Nickel Doping on ZIF-Derived Oxygen Reduction Catalysts for Zinc???Air Batteries

The advancement of cost-effective, efficient, and durable catalysts to replace high cost Pt-based electrocatalysts are of recent interest, especially to enhance the sluggish oxygen reduction reaction (ORR) in fuel cells and metal???air batteries. Herein, we report self-assembled Co???Ni based nitrogen doped carbon structures (Co???Ni/NC) derived from zeolitic imidazolate frameworks as a highly efficient and durable ORR catalyst for rechargeable zinc???air batteries (ZAB). An effective three-phase boundary is recognised with a well-organized interconnected porous carbon framework of the Co???Ni/NC catalyst. The developed catalyst exhibited much improved onset and half-wave potentials (0.93 V and 0.86 V vs. RHE, respectively) in alkaline electrolyte, especially in the limiting current region, which was credited to the porous structure. Furthermore, excellent durability was found for the catalyst operated using continuous potential cycles for 5,000 times and chronoamperometric measurements for 50 h. Finally, the optimised Co???Ni/NC catalyst was successfully utilised as a cathode catalyst and delivered substantial power density in ZAB configuration under ambient operating conditions. Substantial battery durability was also observed over 1000 h by periodically replacing the anodic zinc electrode. Hence, the present investigation offers the prospect of the development of new non-precious, highly active, and durable oxygen reduction catalysts for zinc air battery applications

Cobalt Nanoparticle-Embedded Nitrogen-Doped Carbon Catalyst Derived from a Solid-State Metal-Organic Framework Complex for OER and HER Electrocatalysis

Electrochemical water splitting is considered a promising way of producing hydrogen and oxygen for various electrochemical energy devices. An efficient single, bi-functional electrocatalyst that can perform hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) is highly essential. In this work, Co@NC core-shell nanoparticles were synthesized via a simple, eco-friendly, solid-state synthesis process, using cobalt nitrate and with pyrazole as the N and C source. The morphological analysis of the resulting Co@NC nanoparticles was performed with a scanning and transmission electron microscope, which showed Co nanoparticles as the core and the pyrolysis of pyrazole organic ligand N-doped carbon derived shell structure. The unique Co@NC nanostructures had excellent redox sites for electrocatalysis, wherein the N-doped carbon shell exhibited superior electronic conductivity in the Co@NC catalyst. The resulting Co@NC nanocatalyst showed considerable HER and OER activity in an alkaline medium. The Co@NC catalyst exhibited HERs overpotentials of 243 and 170 mV at 10 mA∙cm−2 on glassy carbon and Ni foam electrodes, respectively, whereas OERs were exhibited overpotentials of 450 and 452 mV at a current density of 10 and 50 mA∙cm−2 on glassy carbon electrode and Ni foam, respectively. Moreover, the Co@NC catalyst also showed admirable durability for OERs in an alkaline medium

Carbon Nanofibers Encapsulated Nickel-Molybdenum Nanoparticles as Hydrogen Evolution Catalysts for Aqueous Zn-CO2 System

Carbon capture, utilization and storage techniques have been studied extensively to reduce atmospheric carbon dioxide. However, CO2 conversion technologies are not widely proposed due to sluggish conversion rate, high energy consumption and need for precious metals as catalysts. Therefore, novel metal-CO2 electrochemical cell has been proposed to utilize CO2 to produce electricity and H-2 gas continuously. Electrochemical hydrogen evolution reaction under neutral condition has demanded the overall device performance. Herein, we have developed non-precious NiMo-carbon nanofiber-based catalyst with unique matchstick-like morphology using low temperature CVD technique and demonstrated in aqueous Zn-CO2 system. The NiMo alloy offers excellent activity by promoting hydrogen adsorption/desorption and chemically bonded carbon nanofiber assists catalytic activity by providing charge transfer. Due to superior characteristics, NiMo-carbon nanofiber exhibits significant HER activity (over-potential of 268 mV at 10 mA cm(-2)) in CO2-saturated 1 M KOH and superior cell performance in aqueous Zn-CO2 system (peak power density of 25 mW cm(-2)). In addition, the stability of the catalysts has also been investigated using chronopotentiometry and the results have compared with commercial Pt/C catalysts. We are hopeful that the present study will provide insights into developing non-precious electrocatalysts, particularly for metal-CO2 electrochemical conversion devices