Enhanced photoelectrochemical water splitting via 3D flow field structure: unveiling the decisive role of interfacial mass transfer

The efficiency of photoelectrochemical water splitting is not only related to the electrode material, but also influenced by the mass transport at the electrode surface. Here, we design a novel photoelectrochemical water splitting reactor, which generates a turbulent flow (0-145 mL/min) at the electrode/electrolyte interface. It was revealed that the reactor has a significant effect on the electrolyte flow, and the flow rate on the photocurrent density was more significant during the transition period of the flow state and the high flow rate. The 3D flow field structure improved the water splitting reaction of TiO2 photoelectrode by 130% at the flow rate of 130 mL/min, and consequently, the TiO2 exhibited a photocurrent density of 0.142 mA·cm-2 at 1.23 V versus the reversible hydrogen electrode. Then we changed the temperature (20-90 ℃) of the electrolyte, and electrochemical impedance spectra results indicated that ion transport impedance decreased with increasing electrolyte temperature in the test range. The photocurrent density increased by about 2.2 times at 90 °C compared to that at 20 °C. This work provided insights of the structure design on the photoelectrode/electrolyte in solar water splitting and revealed the non-negligible effect of interfacial mass transport in photoelectrochemical measurement.