Effect of the Anionic Counterpart: Molybdate vs. Tungstate in Energy Storage for Pseudo-Capacitor Applications

Nickel-based bimetallic oxides (BMOs) have shown significant potential in battery-type electrodes for pseudo-capacitors given their ability to facilitate redox reactions. In this work, two bimetallic oxides, NiMoO(4) and NiWO(4), were synthesized using a wet chemical route. The structure and electrochemical properties of the pseudo-capacitor cathode materials were characterized. NiMoO(4) showed superior charge storage performance in comparison to NiWO(4), exhibiting a discharge capacitance of 124 and 77 F·g(−1), respectively. NiMoO(4), moreover, demonstrates better capacity retention after 1000 cycles with 87.14% compared to 82.22% for NiWO(4). The lower electrochemical performance of the latter was identified to result from the redox behavior during cycling. NiWO(4) reacts in the alkaline solution and forms a passivation layer composed of WO(3) on the electrode, while in contrast, the redox behavior of NiMoO(4) is fully reversible.