Large-Area WO₃/BiVO₄-CoPi Photoanode for Efficient Photoelectrochemical Water Splitting: Role of Patterned Metal Microgrid and Electrolyte Flow

The WO 3 /BiVO 4 heterojunction-based photoanodes have demonstrated great potential in the field of photoelectrochemical (PEC) water splitting. The advancement in large-area photoanodes is impeded due to the resistive loss of transparent conducting oxide (TCO) substrate, nonhomogeneity in the photoactive films, nonuniform deposition of co-catalyst, and pH gradient across the electrode. Herein, the patterned metal microgrid is sputtered under the WO 3 /BiVO 4 heterojunction to reduce resistive losses and improve the uniformity of distributed potential in large-area substrates (5 cm × 5 cm). A good decoration of the photoelectrodeposited CoPi is obtained owing to the uniformity of the potential drop across the substrate with metal microgrid and electrolyte flow at rather high current densities (>2 mA/cm 2 ). The patterned microgrid prepared by lithography-based micropatterning suppressed the loss of photoactive area. The combination of (i) metal microgrid with the large-area TCO substrate, (ii) synthesis of large-area WO 3 /BiVO 4 heterojunction with high homogeneity, (iii) flow-induced uniform photoelectrodeposition of CoPi, (iv) and an engineered PEC cell design with electrolyte flow improved the photocurrent of large-area photoanodes. The simulation studies were performed to investigate the role of potential drop and electrolyte flow in the performance of large-area photoanode. The photoanode exhibited enhanced stability owing to the replenishment of the H + /OH – species near the electrode surface, facilitating rapid bubble detachment from the photoanode. The electrochemical engineering strategies resulted in an excellent photocurrent density of 2.8 mA/cm 2 with a long-duration stability of 80 h in a large-area photoanode. The study provides guidelines for implementing electrochemical engineering strategies to achieve enhanced PEC performance of large-area photoanode.