OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. ) redox processes. The structural evolutions during cycling have been followed and found to be associated with the cation disordering and loss of crystallinity on cycling.

In this work, we have studied a 2% copper substituted core shell type iron/iron carbide as a negative electrode for application in energy storage. The NanoFe-Fe 3 C-Cu delivered 367 mAh g −1 at ≈80% current efficiency, successfully running for over 300 cycles. The superior electrode kinetics and performance were assessed by rate capability, galvanostatic, potentiodynamic polarization measurements in 6 M KOH electrolyte and at ambient temperature. Ex-situ XRD characterizations and SEM images of both the fresh and used electrode surfaces show that nanoparticles were found to be still intact with negligible particle agglomeration. The electrodes have shown stable performances with low capacity decay, whereas sulfur dissolution from the additive Bi 2 S 3 was found to decrease the charging efficiency with time. This core-shell type structured nano material is, consequently, an auspicious anode candidate in alkaline-metal/air and Ni-Fe battery systems. Electricity generation away from fossil fuels by renewable energy resources (RER) is increasing at a remarkable pace both as a means of mitigating greenhouse gas emissions as well as offsetting the global energy demand for sustainable development. Since the end of the 1990s, the world cumulative energy generation by both wind and solar has shown an exponential growth rate. In 2015, the global installed capacity of photovoltaics was 227.1 GW an increase by 25% and the total installed wind power was 432.9 GW, a rise by 17% compared to 2014 for both energy systems.1,2 However, both wind and solar are very dependent on weather conditions and there is a high quest for electrical energy storage (EES) for integration with these renewables. The variability in energy output is due to the stochastic nature and availability of the renewable sources, unreliable demand and supply of electricity, distributed energy generation, maintenance and utilization of load balance in peak shaving and leveling, stabilization of transmission and distribution to the grid, uninterruptable power supply with frequency control, voltage fluctuations and energy arbitrage. EES is considered to be vital and indispensable technology for both utility and transport applications.1,3-7 Among EES technologies, electrochemical energy storage systems in the form of batteries have characteristic features in the form of modularity and scalability, fast response time and high energy efficiency, although they do significantly differ in energy and power densities, charge and discharge duration, cycling behavior and capital cost.There are several rechargeable (secondary) battery energy storage systems (BESS) that are widely used or are under demonstrations/development phases and these among others include; lead-acid, Li-ion, the nickel-based batteries (Ni-MH, Ni-Cd, Ni-Fe, Ni-Zn, NaNiCl 2 ), redox flow batteries (Vanadium, Zn-Br, Zn-Cl, Zn-Ce, FeCr, V-Br), NaS and Air-metal batteries (Fe-air, Zn-air, Li-air, Mgair).6-10 The last type of "batteries" are essentially a hybridization of anodes in the form of metals and a f...

This article reports the two-step synthesis of NiFeOx nanomaterials and their characterization and bifunctional electrocatalytic activity measurements in alkaline electrolyte for metal-air batteries. The samples were mostly in layered double hydroxide at the initial temperature, but upon heat treatment, they were converted to NiFe2O4 phases. The electrochemical behaviour of the different samples was studied by linear sweep voltammetry and cyclic voltammetry on the glassy carbon electrode. The OER catalyst activity was observed for low mass loadings (0.125 mg cm−2), whereas high catalyst loading exhibited the best performance on the ORR side. The sample heat-treated at 250 °C delivered the highest bi-functional oxygen evolution and reduction reaction activity (OER/ORR) thanks to its thin-holey nanosheet-like structure with higher nickel oxidation state at 250 °C. This work further helps to develop low-cost electrocatalyst development for metal-air batteries.