Low-Cost Nanomaterials for Photoelectrochemical Water Splitting - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 282

Mo as n type dopants [ 69 , 113 - 115 , 121 ]. Recently, Wang et al. also demonstrated
that hydrogen treatment increased the carrier density of BiVO 4 and improved its
photoactivity for PEC water oxidation.
4 Conclusion
In this chapter, we have highlighted the recent research achievements in devel-
oping low-cost metal oxide nanomaterials for PEC water splitting. In comparison
to bulk or planar structure, nanostructured materials exhibit larger surface area,
shorter carrier diffusion distance, and lower light reflectivity; all these advantages
make nanostructures to be more promising photoelectrodes for PEC water spitting
application. A number of strategies, such as morphology engineering, element
doping, sensitization, and chemical modifications have been developed to address
the intrinsic limitations of metal oxides in light absorption, charge separation, and
transport. Although significant process has been made in the past decades, there
are still several outstanding challenges remain in order to commercialize the
photoelectrodes for PEC water spitting. The cost, efficiency, and long-time sta-
bility are still the most important issues that need to be further improved. To date,
the overall efficiency of metal oxides for PEC water splitting is still relatively low
(\2 %); and there is not a single semiconductor material could meets all the
requirements for a high efficient photoelectrode. A possible solution to the prob-
lem is to develop new nanomaterials and device architectures. It is promising to
develop semiconductor alloys such as ternary or quaternary metal oxide nano-
structures, which allow the band-gap and band-edge positions to be engineerable
for maximizing the efficiency for water splitting. Additionally, it is equally
important to develop simple and low-cost synthetic methods to fabricate these
nanostructures with controlled optical and electronic properties.
References
1. Ahn S, Kim K, Cho A, Gwak J, Yun JH, Shin K, Ahn S, Yoon K (2012) CuInSe 2 (CIS) thin
films prepared from amorphous Cu-In-Se nanoparticle precursors for solar cell application.
Acs Appl Mater Inter 4(3):1530-1536
2. Alfano OM, Bahnemann D, Cassano AE, Dillert R, Goslich R (2000) Photocatalysis in
water environments using artificial and solar light. Catal Today 58(2-3):199-230
3. Barroso M, Cowan AJ, Pendlebury SR, Gratzel M, Klug DR, Durrant JR (2011) The role of
cobalt phosphate in enhancing the photocatalytic activity of alpha-Fe 2 O 3 toward water
oxidation. J Am Chem Soc 133(38):14868-14871
4. Cai QY, Paulose M, Varghese OK, Grimes CA (2005) The effect of electrolyte composition
on the fabrication of self-organized titanium oxide nanotube arrays by anodic oxidation.
J Mater Res 20(1):230-236