Strategies for improving photoelectrochemical water splitting performance of Si‐based electrodes

Abstract

Si, as a narrow bandgap semiconductor with a broadband absorption for sunlight, is considered to be a very competitive photoelectrode material for solar-driven photoelectrochemical (PEC) water splitting. However, there are major barriers in construction of efficient and stable Si-based PEC cell, including low photovoltage, sluggish reaction kinetics, and poor stability in electrolytes. This review focuses on the strategies to solve these issues and summarizes recent progress. The working principles of PEC water splitting are first introduced. Then the strategies for improving Si-based photoelectrode performances are discussed, including (1) the regulation of Si surface morphology for enhancing light harvesting, (2) band structure engineering strategies to reduce recombination of photogenerated carriers, and (3) modification of protection layers for long stability and loading cocatalysts on Si-based photoelectrodes for accelerating water splitting. Lastly, we have presented some issues of Si-based photoelectrode materials, which should be addressed in future research.

Review of Laser-Based Surface Nanotexturing for Enhanced Light Absorption and Photoelectrochemical Water Splitting

“…Currently, most of the reports on laser-based textured electrodes are focused on stainless steel, silicon, and titanium substrates. 19 This technique of 3D printing and laser ablation can be extended to a broad range of photoactive materials for fabricating nanostructured photoelectrodes. Figure 12 shows the developmental path of stable photocatalytic systems and electrode fabrication methods with an aim to achieve the highest solar energy conversion efficiency.…”

“…However, the topological and morphological alterations at the semiconductor surface through defect chemistry and patterning can help enhance the catalytic property of photoanodes compared to the bulk catalyst. Such alterations offer various advantages, which include (i) reduced charge transfer pathways, (ii) increased active areas for redox reactions, and (iii) higher light-harvesting efficiency through multiple light reflections and scattering. , Figure shows the effectiveness of nanotextured photoanodes for light absorption and trapping compared to nontextured photoanodes (e.g., thin films). Texturing increases the roughness of the surface and helps to trap light, as shown in Figure .…”

Recent Progress on Photoelectrochemical Water Splitting of Graphitic Carbon Nitride (g−CN) Electrodes

“…To date, n-type semiconductor photoanodes usually exhibit lower photocurrent densities (several mA cm −2 ) under AM 1.5G, which is still much lower than the theoretical values. The semiconductor materials used in overall PEC water splitting must also satisfy specific requirements, which the potential of the conduction band must be more negative than the reduction edge of hydrogen, and the valence band potential must be positive enough to actuate water oxidation (more than +1.23 eV) [ 28 , 29 , 30 ]. Based on the above discussion, we can infer that a moderate band gap (that is, a sufficient light absorption property), suitable energy level positions, efficient electron–hole excitation and separation, minimal overpotential, long-term stability, and cost-effective are the main requirements for a photoelectrode in PEC water splitting device.…”

Exploring CuBi2O4 as a Promising Photocathode Material for PEC Water Splitting

“…Recently, a variety of p-type semiconductors have been employed in photovoltaic devices like c-Si, a-Si, CuInS 2 , CuSbS 2 , BiSbS 3 , Sb 2 S 3 , CuBi 2 O 4 , and Cu 2 ZnSnS 4 due to their outstanding band gap and high rate of light absorption. − Among p-type semiconductors, CBO has been actively studied because of its ability to capture a wide range of solar radiation and their suitable band edge positions for H 2 formation. − Furthermore, it has an onset potential as high as 0.9 V vs RHE, making it a leading photocathode material for PEC water splitting. Despite its potential, the actual photocurrent for water reduction on a CBO photocathode is only 1 mA·cm –2 , which is significantly lower than its theoretical photocurrent (19.5–25.4 mA·cm –2 ) that is calculated using its band gap (1.5–1.8 eV). − The major decrease in photocurrent is primarily caused by high charge recombination and low charge mobility.…”