The Role of Cobalt Phosphate in Enhancing the Photocatalytic Activity of α-Fe₂O₃ toward Water Oxidation

Abstract

Transient absorption spectroscopy was used to probe the dynamics of photogenerated charge carriers in α-Fe(2)O(3)/CoO(x) nanocomposite photoelectrodes for water splitting. The addition of cobalt-based electrocatalysts was observed to increase the lifetime of photogenerated holes in the photoelectrode by more than 3 orders of magnitude without the application of electrical bias. We therefore propose that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.

Cobalt Phosphate Group Modified Hematite Nanorod Array as Photoanode for Efficient Solar Water Splitting

“…The photogenerated hole was quickly transferred to the surface of ␣-Fe 2 O 3 due to the short distance of one dimension nanorod arrays and the phosphate groups also enhanced the transportation from the ␣-Fe 2 O 3 surface to the Co ions because of the larger electronegativity. At the same time, the cobalt was connected closely to the ␣-Fe 2 O 3 NAs by the phosphate groups, which reported by Liu et al [19] Besides, both Barroso and Liu has studied that the CoPi groups increased the kinetic of the water oxidation reaction as a co-catalyst [19,20]. On the other hand, the electron was transported to the substrate.…”

“…However the reported efficiencies of hematite are relatively lower than theoretically predicted value of 12.4%, mainly because of the extremely short photogenerated charge carriers' lifetime and diffusion length, chemically inert oxygen evolution reaction, and low flat band potential [7][8][9]. Various approaches, i.e., manipulating nanostructure [5,10,11], chemical composition doping [8,9,[12][13][14], and surface modification [7,15] have been adopted to enhance the photoelectrochemical efficiency of ␣-Fe 2 O 3 .…”

“…Previous reports show that hematite nanoparticles modified with cobalt phosphate group catalyst by electrochemical method effectively separate and transport the photogenerated holes [19][20][21][22][23][24]. Besides, the Co species are effective catalyst for the oxygen evolution reaction from water due to the generated intermediate species with water oxidation active sites [25].…”

Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis

“…Cobalt oxide overlayers such as CoPi also can increase the lifetime of photogenerated holes in hematite photoanodes, demonstrating that deposition of CoPi on R-Fe 2 O 3 kinetically retards e À /h þ recombination. 28 …”

Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes

“…For example, Durrant and co-workers used transient absorption (TA) spectroscopy to monitor the evolution of surface-trapped holes and correlated a long trapped hole lifetime with the onset of photocurrent. [27][28][29]31 One limitation of TA, however, is the difficulty with assigning the energetics of the system, e.g. the position of the relevant surface states.…”