Integrated photoanode based on silicon carbide nanowire arrays for efficient water splitting

In the context of rapid social development, it is urgent to address the increasingly prominent issues of fossil energy depletion and environmental pollution. As a result, research has focused on the creation of new clean energy sources such as solar, wind, biological, geothermal, and hydrogen. Hydrogen energy is one of these new energy sources that has drawn a lot of attention because of its low weight, good thermal conductivity, high heating value, rich utilization forms, and diverse storage states. Nowadays, one of the most significant methods for producing clean energy is photoelectrochemical (PEC) water splitting for hydrogen. However, the intrinsic drawbacks of commonly used semiconductors, such as the low light absorption efficiency, high carrier recombination rate, and slow oxygen evolution kinetics, have become the main barriers preventing their advancement in PEC water splitting. This study used anodic oxidation to create N-doped 4H-SiC nanowire arrays (NWAs) from N-doped 4H-SiC single crystalline wafers. It can be verified that the highly oriented N-doped 4H-SiC NWAs are fully exposed by removing the cap layer. Additionally, the single bamboo-shaped nanowire that was produced has a diameter of ~30–50 nm. Focusing on the optimization of the oxygen evolution reaction (OER) conditions, the NWAs were used as an integrated photoanode in a typical three-electrode system to achieve effective PEC water splitting for hydrogen production under illumination and electric field. Notably, the N-doped 4H-SiC NWAs show better water splitting performance compared with the bulk; that is, the onset potential is decreased from 1.224 V to −0.021 V versus the Ag/AgCl electrode, and the current density is increased from 2.64 mA∙cm⁻² to 3.61 mA∙cm⁻² at 1.4 V. Particularly, the N-doped 4H-SiC NWAs exhibit an extremely sensitive response to light. The improved optical absorption capacity and efficient charge transfer of N-doped 4H-SiC NWAs are responsible for the improvement in PEC water splitting performance. On the one hand, when the N-doped 4H-SiC NWAs are exposed to light, a significant amount of light shines into the gap between the nanowires. N-doped 4H-SiC obtains additional light absorption pathways with the constant reflection of the light, significantly enhancing the light absorption efficiency. On the other hand, the NWAs can considerably reduce the hole travel distance and avoid the recombination of the photogenerated electron-hole pairs, making more charges participate in the redox reaction to enhance the PEC water splitting performance of N-doped 4H-SiC. By building semiconductor photoanode nanostructures, it is possible to efficiently absorb light and transfer charge, significantly enhancing the PEC water splitting efficiency.