The Preparation Of A Novel Photocathode And Its Performence In Hydrogen Evolution Reaction By Water Splitting

Since the industrial revolution,a large amount of primary energy has been consumed in the process of the social development,resulting in increasingly serious environmental pollution.At the same time,serious energy crisis is a great challenge to China due to the uneven distribution of global energy.Thus,it is urgent to find a clean and efficient energy to replace traditional energy.Hydrogen energy has been regarded to be an environmentally friendly and renewable energy due to the advantage of a wide range of sources,high energy density,and pollution-free of combustion products.The utilization of solar and electrical energy to obtain the hydrogen fuel via photoelectrocatalytic water splitting has been considered to be an effective strategy to solve the energy and global environmental problems.Photocathode is an essential component of photoelectrochemical cell.At present,most investigations of photocathodes focused on semiconductor-based materials,which are used as photocatalytic layer to provide photo-generated charges-carriers.In addition,some precious metal(such as platinum)based materials used as cocatalysts enable the composite catalysts to exhibit an excellent hydrogen-evolution activity.However,some intrinsic nature of semiconductor constrains its photoelectrocatalytic activity.And the electrodes become more expensive due to the utilization of precious cocatalysts.In the future,the development of photocathode materials with low cost,high efficiency and stable durability,and the promotion of the industrialization of photoelectrocatalytic hydrogen production are still the goals of the majority of researchers.In this paper,photocathode materials with high efficiency and stability have been prepared on different conductive substrates(metal titanium foil,molybdenum foil and copper foam)by using in-situ growth method in combination with catalyst design and interface design of electrode.The photocatalytic layer of photocathode was ingeniously designed through the fabrication of titanium dioxide array with open morphology or the introduction of plasmon metal copper nanowires or the other metallic photocatalyst molybdenum nitride.The photoelectrocatalytic performance was further enhanced by loading non-noble metal molybdenum disulfide as cocatalyst.Besides,the morphology and interfacial properties of the photocathode can be optimized by adjusting the preparation process of the electrode.The crystal structure,morphology,optical performance and photoelectrochemical performance of the photocathode were tested and characterized,and the corresponding suitable energy band models were constructed.The mechanisms of the enhanced photoelecteocatalytic performance for composite catalytic systems were analyzed,respectively.The main results of this research are as follows:(1)In-situ grown titanium dioxide coated with molybdenum sulfide composite photocathode was prepared on metal titanium foil by anodic oxidation and electrochemical deposition(v-TiO2@MoS2/Ti foil).The morphological characterization demonstrated that one-dimensional Ti02 nanotube array is uniformly coated with the MoS2 layer inside and outside.Moreover,the unobstructed pathway inside of the composite nanotubes is maintained benefited from vacuum pretreatment.The unique structure offers not only maximally exposed the active sites of MoS2,but also the close contact between TiO2 and MoS2,which is beneficial to enhance the photoelectrocatalytic activity.Compared with the obstructed nano tubular composite catalysts,the unobstructed nanotubes exhibit more efficient visible light absorption.The highly oriented and orthogonal separation of charge carriers between TiO2 nanotube array and MoS2 layer,which is beneficial to the directional migration of photoinduced carriers.Additionally,the heterojunction formed between the TiO2@MoS2 enlarge the solar utilization and suppress the recombination of photoinduced electron-hole pairs.The as prepared vTiO2@MoS2/Ti foil electrode exhibited more efficient and stable photoelectrocatalytic performance for hydrogen evolution reaction.(2)A three-dimensional hierarchical porous structure with onedimensional structure(copper nano wires covered with MoS2)was fabricated on copper foam through a wet chemical method followed by electrochemical deposition approach(Cu NWs@MoS2/Cu foam).The optical properties test demonstrated that the photoelectrocatalytic activity of the photocathode derived from the photogenerated charge-carriers of Cu NWs due to surface plasmon resonance(SPR)effect.Furthermore,the introduction of MoS2 cocatalyst can effectively capture the hot electrons derived from surface plasmon resonance effect.Additionally,Cu NWs can serve as a fast channel for carriers' transfer and a heterojunction formed at Cu/MoS2 interface is of benefit to suppress the recombination of photoinduced carrier,and thus improving photoelectrocatalytic activity.This three-dimensional hierarchical structure with one-dimensional nanowires endows the photocathode with superhydrophilic and superaerophobic properties,which are beneficial for the close contact with electrolyte and the release of as formed gas,and thus providing lager electrochemical active surface area and smaller resistance.In the stability test,the electrode exhibited excellent structural stability and electrochemical stability in the hydrogen evolution reaction,which benefited from the in-situ preparation of the electrode and the formation of mesophase at the interface of Cu NWS and MoS2.(3)Molybdenum nitride has been fabricated on metal molybdenum substance via a facile calcination process under different atmospheres(Mo3N2/Mo foil).The metallic nature and its good optical absorption in the visible light range of Mo3N2 were confirmed by the experimental test and density functional theory calculation.Photocatalytic hydrogen production rate of simplex Mo3N2 reached to 158.78 ?mol h-1 g-1.In order to further improve the photoelectrocatalytic performance of the photocathode,a Mo3N2-MoS2/Mo foil composite photocathode was prepared by the low-temperature surface sulfidation method.A suitable energy band alignment was constructed to explain the origin and mechanism of enhanced photoelectrocatalytic performance.The photocathode exhibited effective photoelectrocatalytic performance mainly originated from the metallic photocatalyst Mo3N2,whose photoinduced charge-carriers can be generated through inter-band transitions under visible light illumination.The suitable energy band structure and Schottky barrier at the interface between Mo2N3 and MoS2 effectively hinder the recombination of photogenerated electron-hole pairs and improves the utilization of photogenerated carriers.At the same time,the introduction of MoS2 provides more active sites for hydrogen evolution,which comprehensively improves the efficiency of photoelectrocatalysis.