Physicochemical properties and electrochemical hydrogen storage performance of Li2M(WO4)2 (M = Co, Ni and Cu)

Abstract

In this work, new materials of the Li2M(WO4)2 type with (M = Co, Ni and Cu) have been studied for the first time as electrodes for electrochemical hydrogen storage. The three double tungstates compounds, have been synthesized by a one-step solid-state reaction and carefully characterized, using X-ray diffraction, scanning electron microscopy, UV–visible and FTIR spectroscopy. The presence of a pure and single phase is confirmed by XRD with the Rietveld refinement for all the studied materials, while SEM observation reveals the granular microstructure of these compounds (1-10 μm). Very close energy gaps of 1.60 eV, 1.62 eV and 1.64 eV are respectively attributed to Li2Cu(WO4)2, Li2Co(WO4)2 and Li2Ni(WO4)2. Cyclic voltametry shows the characteristic redox peaks of these samples and clearly elucidates the redox behavior of the battery type. EIS results show good contact between the surface of the studied materials and the H2SO4 electrolyte, with a surface resistance of (~2 Ω/cm2). The charge-discharge galvanostatic cycling gives a specific storage capacity of 120.1 mA h.g−1 Li2Ni(WO4)2, 98.88 mA h.g−1 Li2Co(WO4)2 and 84.44 mA h.g−1 Li2Cu(WO4)2 at 1 A g−1. They also exhibit a good life cycle stability that exceeds 84%–90% of the retention capacity of Li2Ni(WO4)2 after 50 cycles at 1 A g−1.