Yue Sun,Fenqi Du,Donghang Xie,Dongmei Yang,Yang Jiao,Lichao Jia,Haibo Fan
Iron (Fe) was successfully doped in CuWO4 photoanode films with a combined liquid-phase spin-coating method via the dopant sources of Fe(NO3)3, FeSO4 and FeCl3. The microstructure of the prepared films was characterized by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The light absorption and photoelectric conversion properties were evaluated by the UV-visible absorption spectra and monochromatic incident photon-to-electron conversion efficiency. The chemical composition and element combination of the samples were examined by x-ray photoelectron spectroscopy. A linear sweep voltammetric and stability test (I–t) were performed with an electrochemical workstation. The results show that the samples are uniform with a thickness of approximately 800 nm and that the photoelectrochemical performance of the doped films is heavily dependent on the Fe source and dopant concentration. Upon optimizing the doping conditions of Fe(NO3)3 and the optimal source, the photocurrent density in the Fe-doped CuWO4 photoanode film is improved by 78% from 0.267 mA/cm2 to 0.476 mA/cm2 at 1.23 V vs reversible hydrogen electrode. The underlying causes are discussed.
The electrocatalyst coupling with CuWO 4 has resulted in a comparable or worse performance when compared to the bare CuWO 4 . This work attempts to address this challenge by coupling CuWO 4 with NiWO 4 electrocatalyst that can form a Type-II heterojunction with a suitable energy-level alignment allowing for effective hole transfer from CuWO 4 to NiWO 4 electrocatalyst. We applied thermal annealing to the WO 3 nanoplates by adding Cu(NO 3 ) 2 and Ni(NO 3 ) 2 precursors to obtain the CuWO 4 /NiWO 4 composite with common anions. A high surface-to-volume ratio, perfect interface lattice match, suitable energy level alignment, and high electrocatalytic activity were exhibited in the composite. These characteristics led to a 100 mV negative shift on the onset potential compared to the pure CuWO 4 photoanode. Moreover, it featured a 0.7-fold higher photocurrent density than that of the pure CuWO 4 photoanode. Only 9% of photocurrent density decreased after 4 h of photo-irradiation, demonstrating excellent photostability. Our mechanism study demonstrated that NiWO 4 could act as a semiconductor to form a Type-II heterojunction with CuWO 4 , promoting hole transfer from the CuWO 4 valence band to the NiWO 4 . Meanwhile, the NiWO 4 effectively injects the separated holes into the water solution as a promising electrocatalyst, thus enhancing the overall water splitting performance. This work provides an important design consideration by focusing on the corrected level alignment and lattice match for developing the CuWO 4 /electrocatalyst system to work effectively.
Ternary-phase CuWO4 oxide with an electronic band gap of 2.2–2.4 eV is a potential candidate photoanode material for photoelectrochemical (PEC) water splitting. Herein, we present an efficient method to prepare CuWO4 film photoanode by combining hydrothermal method and hybrid microwave annealing (HMA) process. In comparison with conventional thermal annealing (CTA), HMA can achieve CuWO4 thin film within minutes by using SiC susceptor. When the CuWO4 photoanode is prepared by HMA, its PEC water oxidation performance improves from 0.21 to 0.29 mA cm−2 at 1.23 VRHE comparing with the one prepared by CTA. The origin of the enhanced photocurrent was investigated by means of complementary physical characterizations and PEC methods. The results demonstrated that the obtained HMA processed CuWO4 photoanode not only exhibited intrinsic porous nanostructures but also abundant surface hydroxyl groups, which facilitated sufficient mass transport and the charge transfer. Our results highlight the application of HMA for the fast fabrication of porous film photo-electrodes without using sacrificial template.
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