Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Abstract

The preparation of ZnO nanorod films decorated with cobalt-acetate (CoAc) electrocatalyst and its activity for photoelectrolysis of water have been demonstrated. The photochemically prepared CoAc catalyst is chemically and morphologically similar to the electrochemically prepared CoAc catalyst. The on-set potential of oxygen evolution reaction is lower on CoAc-ZnO photoanode in relation to bare ZnO photoanode. There is a three to four fold increase in photooxidation current of OER due to the presence of CoAc co-catalyst on ZnO. Thus, the photochemically prepared CoAc on ZnO is an alternative and efficient co-catalyst for photoelectrochemical oxygen evolution reaction. The enhancement in photocatalytic activity of ZnO by the CoAc catalyst photochemically deposited from acetate buffer solution is significantly greater than the cobalt-phosphate (CoPi) co-catalyst deposited from phosphate buffer solution. Hydrogen is a convenient fuel for the future owing to its high energy density and eco-friendliness.1,2 Currently, around 48 million metric tons of H 2 is produced globally each year mainly from natural gas by steam-methane reforming method. 3,4 As this process leads to the emission of a large amount of CO 2 (240 mega tons per year), it is challenging to develop alternate, clean methods to produce hydrogen. Generation of hydrogen gas from water requires energy of 273 kJ mol −1 . If this energy is available from a renewable energy source such as solar energy, hydrogen can be considered as an economical and green energy source, which is an alternative to fossil fuels.A simple approach is to use photovoltaic cells to power water electrolyzers. However, diurnal variation in the sunlight intensity, a high cost and a low conversion efficiency impede successful commercialization of the present photovoltaic cells. 5 Another approach is to store solar energy directly in the chemical bonds of small molecules, similar to the photosynthesis route adopted by vegetation. A typical example is the photodissociation of water to generate hydrogen fuel. 6 The first report on photodissociation of water into H 2 and O 2 using ntype TiO 2 photoanode and Pt black cathode was reported by Fujishima and Honda 7 in 1972. Following this report, numerous investigations have been reported for photocatalytic and photoelectrochemical water splitting.8 Most of the studies suffer from poor solar to hydrogen conversion efficiency due to fast recombination of photogenerated charge carriers and poor catalytic activity of semiconductor electrodes toward multi-electron oxygen evolution reaction (OER) at the photoanode. 8,9 Several metal oxides such as RuO 2 , 10,11 IrO 2 12,13 etc., are coupled with semiconductor anodes (TiO 2 , ZnO, etc.) as co-catalysts to enhance the sluggish kinetics of water oxidation. However, high cost of Ru and Ir limit their widespread application. Recently, a cobaltphosphate complex (CoPi) are no reports on the photochemical deposition of CoAc catalyst on a n-type semiconductor electrode and its utilization as a co-catalyst i...

Energy-Inexpensive Galvanic Deposition of BiOI on Electrodes and Its Conversion to 3D Porous BiVO4-Based Photoanode

“…Thus, the metal oxide semiconductors such as ZnO and TiO 2 were usually developed through this technique. , However, in the case of Bi 3+ reduction, metallic deposition is preferred over nitrate reduction because of its more positive reduction potential . Therefore, the electrodeposition of BiOI, an important precursor to highly efficient and porous BiVO 4 , would be quite challenging.…”

“…72 Furthermore, the synergistic effect of Pi and Ac leads to an improved catalysis. Thus, CoAc as OER cocatalyst was reported for various photoanodes such as ZnO and α-Fe 2 O 3 , 30,73 but only a few were reported for bismuth vanadate. 74 Hence, it was chosen as the model catalyst for our photoanode, which was deposited through the photodeposition technique.…”

Photosynthesis-Inspired Acceleration of Carrier Separation: Co–O–Ac and CH3COO– Ions Synergistically Enhanced Photocatalytic Hydrogen Evolution of Graphitic Carbon Nitride

“…In the present research, g-C 3 N 4 was prepared using a previously reported method. , The typical two-dimensional (2D) structure was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Figure S1). Co–O–Ac cocatalyst was loaded onto the surface of g-C 3 N 4 using an in situ artificial photosynthetic method, during which photoexcited holes of g-C 3 N 4 , as the driving force, oxidize Co 2+ ions to Co 3+ ions, and thus, precipitates are deposited onto the surface of g-C 3 N 4 because of the limited solubility of Co 3+ ions. , The valence band edge of g-C 3 N 4 is located at 2.38 V determined by the UV–vis absorption spectrum and ultraviolet photoelectron spectroscopy (UPS) (Figure S2). Given that the standard redox potential of Co 3+ /Co 2+ is about 1.13 V, , the photogenerated holes of g-C 3 N 4 have enough potential to trigger the oxidation of Co 2+ ions.…”

Controllablein situphoto-assisted chemical deposition of CdSe quantum dots on ZnO/CdS nanorod arrays and its photovoltaic application

“…The series of experiments carried out previously have revealed a significant influence of incident light on the formation of CdSe on the ZnO/CdS substrates. To understand these phenomena and investigate their further development, we hereby carried out a mechanism discussion based on the following model according to the results and normal understanding of photochemical processes [32,[51][52][53]: ( )…”