Visible-Light-Enhanced Electrocatalytic Hydrogen Evolution Using Electrodeposited Molybdenum Oxide

Electrocatalytic hydrogen production using inexpensive catalysts and solar energy has become a critical research direction due to its economic interest and environmental friendliness. Photoresponsive semiconductors play a key role in this field. In this work, we demonstrate visible light-responsive, mixed-valence, molybdenum oxide (MoO3-x, 0 <= x <= 1) thin films with oxygen vacancies that are electrochemically deposited in a period of seconds through an ammonium heptamolybdate electrolyte. XRD, XPS, SEM, TEM, EPR, Raman, and electrochemical techniques (Linear Sweep Voltammetry, Chronoamperometry, Electrochemical Impedance Spectroscopy, Tafel analysis) have been utilized to characterize the MoO3-x films. Diffuse reflectance spectroscopy (DRS) and the Mott-Schottky (MS) plot reveal that the as-deposited semiconductive MoO3-x film possesses an optical bandgap of similar to 2.53 eV and a flat band potential of similar to 0.40 eV, respectively. The MoO3-x films exhibit up to 152% electrocatalytic current improvement in the hydrogen evolution reaction (HER) upon illumination with visible light compared to in the dark. The superior electrocatalytic activity of the as-deposited MoO3-x films under illumination is attributed to the lower bandgap, lower overpotential, decreased electronic resistivity, and a smaller Tafel slope. Our experimental exploration suggests that MoO3-x can be potentially applied as an effective, low-cost electrode material for high-performance solar energy-assisted hydrogen fuel production.