Preparation And Photoelectrocatalytic Property Of Ni-SiC Nanowire Composite Electrodes

As a novel photoelectrocatalytic material, zinc blende silicon carbide（3C-SiC） has attracted considerable attention due to its appropriate band gap of 2.4 e V and high chemical stability. Semiconductor-coupled metal or their compounds heterostructured photoelectrocatalysts can effectively promote the electron-hole separation for photoelectrocatalyitc hydrogen evolution due to its innovative structure, unique optical properties. In this paper, Ni/SiC and Ni₃S₂/SiC nanowires film composite electrodes were synthesized by electrodeposition approach. The photoelectrocatalytic activity for hydrogen production of the films was investigated.In this paper, SiC nanowires film were synthesized by the carbothermal reduction method. The expandable graphite, silicon metal powder and tetraethoxysilane were used as the raw materials, and graphite paper were used as the substrate. Ni/SiC, Ni₃S₂/SiC composite electrodes were prepared by electrodeposition method. The microstructure of the products was characterized by XRD, FESEM and UV-vis spectrophotometer. The photoelectrocatalytic performance was investigated. The catalytic mechanism of composite electrodes has been also discussed. The conclusions are listed as follows:Ni/SiC nanowires film was prepared by galvanostatic electrodeposition method. XRD results showed that the crystal phase of product were 3C-SiC and Ni; FESEM results showed that nanowires film is cotton-like, thickness of film is in the range of 30-50 nm. Ni metal nanoparticles deposited on surface of SiC nanowires more evenly distributed with the deposition time of 4 min and distribution of particle diameter is is in the range of 50-100 nm; The UV-vis curves showed the Ni/SiC composite electrode has a stronger absorption of light rays in the range of 300-800 nm compared to pure SiC nanowires film.The photoelectrocatalytic performance of Ni/SiC electrode has been investigated. In 1 M KOH solution, the LSV curves of the Ni/SiC electrode with the different deposition time has been tested at 25 ℃, the results showed the highest photocurrent density of Ni/SiC with which deposition time of 4 min is 32.5 mA?cm-2, and is approximately 10.8 times over the pure SiC. At a constant applied potential of 1.4 V vs. Ag/AgCl, the electrodes still has effective and stable catalytic activity after continuous experiments of 600 s. The catalytic mechanism for photoelectrocatalytic of the Ni/SiC nanowires has been discussed. As the SiC nanowire film excites and produce photo-generated electronic by absorbing the energy of photons, the electrons will be transferred from the conduction band of SiC to the conduction band of Ni quickly and reduce the recombination rate of the photogenerated charges efficiently.Ni₃S₂/SiC nanowires film was prepared by galvanostatic electrodeposition method. XRD results showed that the crystal phase of product were 3C-SiC and Ni₃S₂; FESEM results showed that the Ni₃S₂ alloy covered on the surface of SiC nanowires;Surface of the nanowires with the deposition time of 10 min are smooth and the diameter increased about 20 nm; The UV-vis curves showed the Ni₃S₂/SiC composite electrodes has a stronger absorption of light rays in the range of 300-800 nm compared to pure SiC nanowires film.The photoelectrocatalytic performance of Ni₃S₂/SiC electrode has been investigated. The Ni₃S₂/SiC catalyst shows the highest photocurrent density of 78.6 mA?cm-2 for water splitting, which is approximately 26.2 times over the pure SiC. The electrodes still have stable catalytic activity after continuous experiments of 600 s. The catalytic mechanism for photoelectrocatalytic of Ni₃S₂/SiC nanowires has been also discussed. Due to potential difference between the Ni₃S₂ and SiC, the photogenerated electrons of SiC will transfer to Ni₃S₂. And the action of external voltages can transfer electrons to the cathode, further promote the separation of photo-generated electron-hole pairs effectively, thus increasing the catalytic properties of electrodes.