The Study Of High Efficient And Stable Si Photocathodes For Solar Water Splitting

Fossil fuels are non-renewable sources of energy.And as a result of the massive use of fossil fuels,the earth's fossil fuel resources are drying up.In addition,the burning of fossil fuels causes serious world problems such as environmental pollution,ecological deterioration and climate change.These situations urge us to look for clean and environmentally sustainable new energy sources,among which the use of solar energy to decompose water into hydrogen has become the focus of many studies.Firstly,solar and water are both harmless and sustainable as feedstock for hydrogen production.Secondly,the conversion of solar energy into hydrogen is theoretically not influenced by geography,environment and raw materials.Thirdly,the product H₂ produced are of high calorific value,easy to store and transport,and the combustion products are water.Therefore it is a kind of ideal new energy.Because the H+ and OH-in the aqueous solution can't gain or lose electrons by themselves,the light from the sun's radiation to the earth's surface cannot directly disintegrate the water.Therefore,we need to use the semiconductor electrode to realize the water splitting,and the quality of the electrode determines the ability of hydrogen production by solar water splitting.The determinants are efficiency,stability,and cost.Based on the advantages of Si semiconductor in the field of solar cell,such as high efficiency and low cost.The focus of this paper is to prepare a high efficient and stable Si photocathode by combining the appropriate catalyst and passivation protective layer.?1?The high efficiency and stability of the Si photocathode is achieved by optimizing the surface of the Si wafer,optimizing the catalyst,and combining with the Ti O₂ protection and passivation layer.The optimization of the Si wafer was carried out on the n⁺np⁺ crystalline Si with pyramid surface,whose front surface doped with phosphorus and rear surface doped with aluminum.They were annealed in the atmosphere of mixture gas hydrogen and argon to passivate the surface and improve the open circuit voltage.Secondly,we modified the existing method for non-electrode liquid phase deposition of Pt catalyst which is found to be smaller and more uniform.In addition,the consumption of Pt is reduced while achieving higher efficiency of H₂ production.Finally,atomic layer deposition was used to prepare a layer of 15 nm Ti O₂ on the electrode surface,which increased the stability of the photocathode while ensuring the efficiency.Then we achieved 11.5% efficiency and 168 h stability.The results have been published in Chemical Communications.?2?Pt is the best catalyst for H₂ production,but it is a precious metal.In order to reduce the cost,non-noble metal catalysts have always been the focus of research,and the two dimensional materials represented by MoS₂ have attracted attention due to its excellent catalytic properties.In this paper,the catalytic effect of MoSe₂,WSe₂ and its composite Mo_0.5W_0.5Se₂ on the decomposition of water by Si photocathode were studied.We sputter these materials with different time on n⁺np⁺-Si substrate by pulse laser deposition.Then,we test their photoelectrochemical properties.We have successfully deposited the Mo_0.5W_0.5Se₂ composite onto the Si photocathodes to decompose water,achieving an efficiency of 3.8%,much higher than those obtained in MoSe₂ and WSe₂ catalyzed Si photocathodes.