Photoelectrochemical hydrogen generation using gradient-bandgap semiconductor arrays for improved solar energy conversion and water splitting efficiency

Abstract

Photoelectrochemical (PEC) water splitting offers a promising route for solar hydrogen production, but current systems suffer from limited light absorption, poor charge separation, and inadequate stability. This study aimed to develop a novel gradient-bandgap semiconductor array architecture to overcome these fundamental limitations and enhance solar-to-hydrogen (STH) conversion efficiency. Gradient-bandgap semiconductor arrays were fabricated via atomic layer deposition, creating sequential layers of TiO₂, WO₃, and BiVO₄ with compositionally graded interfaces. XRD, HRTEM, XPS, and UV–vis spectroscopy provided photoelectrode characterization. Under simulated AM 1.5G illumination, the photoelectrochemical capabilities were assessed via intensity-modulated photocurrent spectroscopy, electrochemical impedance spectroscopy, incident photon-to-current efficiency, and current-voltage measurements. The gradient-bandgap architecture attained a STH conversion efficiency of 12.32 %, representing a 7.1-fold improvement over single-material BiVO₄ photoelectrodes (1.73 %). Photocurrent density reached 16.78 mA/cm² at 1.23 V versus reversible hydrogen electrode, with a corresponding hydrogen evolution rate of 6.21 mmol/h·cm². The photoelectrode demonstrated exceptional stability, retaining 95.1 % of its initial performance after 200 h of continuous operation. Charge transfer efficiency reached 90.4 %, significantly higher than the 59.2–75.8 % observed in single-material electrodes, while carrier lifetime extended to 18.3 ns (39–115 % improvement over individual components). The gradient-bandgap semiconductor array design successfully addresses the critical limitations of conventional photoelectrodes through synergistic integration of complementary materials with engineered interfaces. This approach provides a practical pathway toward high-efficiency, durable, and economically viable solar hydrogen production without requiring expensive noble metal catalysts.