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

The WO3/BiVO4 heterojunction-based photoanodes have demonstrated great potential in the field of photo electrochemical (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 WO3/BiVO4 heterojunction to reduce resistive losses and improve the uniformity of distributed potential in large-area substrates (5 cm x 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/cm2). 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 WO3/BiVO4 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/cm2 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.