Abstract
Photoelectrochemical (PEC) water splitting using solar energy has attracted great attention for generation of renewable hydrogen with less carbon footprint, while there are enormous challenges that still remain for improving solar energy water splitting efficiency, due to limited light harvesting, energy loss associated to fast recombination of photogenerated charge carriers, as well as electrode degradation. This overview focuses on the recent development about catalyst nanomaterials and nanostructures in different PEC water splitting systems. As photoanode, Au nanoparticle-decorated TiO2 nanowire electrodes exhibited enhanced photoactivity in both the UV and the visible regions due to surface plasmon resonance of Au and showed the largest photocurrent generation of up to 710 nm. Pt/CdS/CGSe electrodes were developed as photocathode. With the role of p–n heterojunction, the photoelectrode showed high stability and evolved hydrogen continuously for more than 10 days. Further, in the Z-scheme system (Bi2S3/TNA as photoanode and Pt/SiPVC as photocathode at the same time), a self-bias (open-circuit voltage V oc = 0.766 V) was formed between two photoelectrodes, which could facilitate photogenerated charge transfers and enhance the photoelectrochemical performance, and which might provide new hints for PEC water splitting. Meanwhile, the existing problems and prospective solutions have also been reviewed.
Highlights
The energy consumption nowadays to maintain modern lifestyle of mankind mainly relies on primary fossil fuels such as oil, coal, natural gas, etc
In comparison with photocatalytic water splitting using heterogeneous powder semiconductors, PEC water splitting possesses great advantages in (i) the external or self-bias voltage can suppress recombination of photogenerated charge carriers and improve the separation and transfer of excited electron–hole pairs of the photocatalysts; (ii) hydrogen and oxygen can be separated via collection at different photoelectrodes; (iii) semiconductor films are coated on the conductive substrates, which favors scale up for industrial application in the future; and (iv) last, but not the least, it does not need stirring, so it consumes less power relative to powder photocatalytic water splitting systems [2, 5]
The metal sulfides have been found as a class of efficient photocatalysts but require sacrificial agents to reduce photocorrosion [8,9,10,11,12]. (Oxy) nitride semiconductors recently emerged as new type of phototcatalysts for visible-light-responsive photocatalytic water splitting [13,14,15], whereas they can respond to short-wavelength visible light with rather low solar energy conversion efficiency
Summary
The energy consumption nowadays to maintain modern lifestyle of mankind mainly relies on primary fossil fuels such as oil, coal, natural gas, etc. This discovery stimulated great interest to explore effective photoelectrode materials for solar energy hydrogen generation via solar energy water splitting which is a clean process and stores solar energy in hydrogen [2,3,4]. The performance of PEC water splitting system is dominated by the properties of the semiconductor photocatalysts that harvest solar energy for hydrogen generation. (Oxy) nitride semiconductors recently emerged as new type of phototcatalysts for visible-light-responsive photocatalytic water splitting [13,14,15], whereas they can respond to short-wavelength visible light with rather low solar energy conversion efficiency. The hybrid photocatalyst systems have demonstrated enhanced water splitting efficiency, which, require dedicated design and alignment of the corresponding photocatalytic materials [6]. Key issues and challenges involved in PEC water splitting systems and potential solutions were highlighted via the comparison of various photoelectrode materials and nanostructures
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