For photoelectrochemical (PEC) water splitting, the interface interactions among semiconductors, electrocatalysts, and electrolytes affect the charge separation and catalysis in turn. Here, through the changing of the bath temperature, Co-based oxygen evolution catalysts (OEC) with different crystallinities were electrochemically deposited on Ti-doped FeO (Ti-FeO) photoanodes. We found: (1) the OEC with low crystallinity is highly ion-permeable, decreasing the interactions between OEC and photoanode due to the intimate interaction between semiconductor and electrolyte; (2) the OEC with high crystallinity is nearly ion-impermeable, is beneficial to form a constant buried junction with semiconductor, and exhibits the low OEC catalytic activity; and (3) the OEC with moderate crystallinity is partially electrolyte-screened, thus contributing to the formation of ideal band bending underneath surface of semiconductor for charge separation and the highly electrocatalytic activity of OEC for lowering over-potentials of water oxidation. Our results demonstrate that to balance the water oxidation activity of OEC and OEC-semiconductor interface energetics is crucial for highly efficient solar energy conversion; in particular, the energy transducer is a semiconductor with a shallow or moderate valence-band level.

This work investigates the pulsed breakdown processes and mechanisms of self-triggered pre-ionized switches with a four-electrode structure in nitrogen through ICCD (Intensified Charge Coupled Device) photographs. The diameter of the trigger plane hole mainly determines the switch’s electric field distribution. Two configurations with minimum and maximum trigger plane holes are adopted for comparison. In the switch with a minimum trigger plane hole, the maximum electric field distributes at the surfaces of the main electrodes. Though charged particles in the triggering spark channel cannot drift out, homogeneous discharges can be stimulated from both the cathode and anode surfaces through UV (ultraviolet) illumination. Two sub-gaps are likely to break down simultaneously. In the switch with a maximum trigger plane hole, the maximum electric field locates near the trigger electrodes. Discharges in both sub-gaps initiate from the trigger electrodes in the form of a positive or negative streamer. Due to lower breakdown voltage and electric field threshold for discharge initiation, the cathode side sub-gap breaks down first. The analysis of two extreme examples can be referenced in the future design and improvement of self-triggered four-electrode switches with different structures of trigger electrodes.