Fabrication and evaluation of binder-free metal-molybdate electrodes for improved energy storage and hydrogen evolution applications

The investigation focuses on the development, comprehensive characterization, and electrochemical testing of three novel binder-free electrodes based on nickel (Ni), manganese (Mn), and molybdenum dioxide (MoO₄) on three dimensional nickel foam (3DNF): 3DMn-MoO₄@3DNF, 3DNi-MoO₄@3DNF, and 3DNi/Mn-MoO₄@3DNF. These electrodes are synthesized via hydrothermal methods, followed by annealing to form 3D metal-molybdate structures on nickel foam substrates. Hexamethylenetetramine (HMTA) and urea serve as directing agents, controlling the morphology and structural growth of the nanosheets. Advanced characterization techniques confirm the presence of nickel and manganese molybdate phases, providing insights into their crystal structures, surface morphologies, and elemental compositions. Electrochemical testing, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy, reveals that the 3DNi/Mn-MoO₄@3DNF electrode exhibits the highest specific capacitance at 2710.0 F/g and the lowest hydrogen evolution overpotential at 249 mV. This superior performance is attributed to the synergistic effects of nickel and manganese ions and the optimized microstructure, enhancing active site availability and electron and ion transport. The study demonstrates the critical role of synthesis conditions and directing agents such as urea and HMTA in influencing nanosheet morphology, thereby affecting the electrodes' porosity, surface area, and electrochemical activity, highlighting their potential in energy storage and conversion applications.