Visible Light Driven Photoelectrochemical Water Oxidation by Zn- and Ti-Doped Hematite Nanostructures

Abstract

The electrodeposition method was used for modification of a nanostructured hematite photoanode with Ti and Zn to improve the photoelectrocatalytic performance of hematite in the water splitting reaction. The photoelectrocatalytic activity of the hematite electrodes modified with Ti 4+ and Zn 2+ was optimized through the controlled variation of the dopant ion concentration in the electrodeposition solution. Under optimized conditions, for standard illumination of AM 1.5G (100 mW cm −2 ), the photocurrent density at the Ti/Zn-modified hematite anode reached 1.5 mA cm −2 at 1.23 V vs RHE that was 2.5-times higher than that observed with the pristine hematite electrode, the photoelectrocatalysis onset potential being 63 mV reduced. Effects of Ti and Zn doping on the photoelectrochemical activity of pristine hematite were studied by scanning electron microscopy, UV−vis spectroscopy, elemental analysis, and electrochemical impedance spectroscopy. On the basis of the obtained results, the improved performance of the Ti/Zn-modified hematite stemmed from the combination of the enhanced electrical conductivity along with the facilitated charge transport in the bulk phase and at the surface of hematite. The effect of Zn-doping decreasing the overpotential of the reaction by 218 mV (solely Zn-doped compared to that of the pristine hematite) was correlated with the Zn contribution to the interfacial catalysis of water oxidation.

Electrodeposited Ti-doped hematite photoanodes and their employment for photoelectrocatalytic hydrogen production in the presence of ethanol

“…The FTO electrodes were cleaned ultrasonically in Millipore water, ethanol, acetone, and finally rinsed in Milli-Q water. Next, the cleaned FTO electrodes were immersed into the electrodeposition solution containing 5 mM FeCl 3 , 5 mM KF, 0.1 M KCl, and 1 M H 2 O 2 [16]. For modification of hematite with titanium (Ti-modified hematite electrode), calculated amounts TiCl 4 were added to the electrodeposition solution to achieve Ti/Fe nominal atomic ratios of 1%, 3%, 5% and 10%.…”

“…A versatile synthesis procedure, allowing performance optimization by doping, has been obtained by the hydrothermal route [11][12][13][14]. An equally versatile, room temperature procedure for hematite film formation and doping is by electrodeposition [6][7][8]15,16]. The last procedure, which is easy to apply and interesting for industrial applications, has been adopted for the purposes of the present work.…”

“…Doping is expected to repair defects and thus decrease electron-hole recombination. Metal doping involves a variety of dopants, for example, Pt [8], Zn and Ti [16]. Another interesting approach is to combine hematite with an oxygen evolution co-catalyst, such as Co-Pi [7].…”

“…In this respect, in the present work, we have studied the applicability of hematite photoanodes beyond water splitting to the production of hydrogen in the presence of organic sacrificial agents. We have employed a standard procedure to construct electrochemically deposited hematite photoanodes doped with Ti 4+ [16]. The content of the present work involves elaboration on the method of hematite film deposition on FTO electrodes, doping with Ti 4+ , film optimization and characterization and presentation of some typical data on photoelectrochemical hydrogen production.…”

g-C3N4 decorated ZnO nanorod arrays for enhanced photoelectrocatalytic performance

“…Compared to the pure ZnO and g-C 3 N 4 , the g-C 3 N 4 /ZnO extends the 15 absorbance to not only the ultraviolet region but also the visible region, suggesting that the recombination rate of the photoinduced electro-hole pairs was successfully reduced in the heterostructured g-C 3 N 4 /ZnO composite. The band gap (E g ) of the ZnO and g-C 3 N 4 can be calculated from the formula: 20 Where α, hν and A is the absorption coefficient, photo energy and constant, respectively [40].…”