Development of the Photoelectrolysis Cell for Energy Storage Using Silicon Electrode

本文研究了利用具有金属包覆p-n结硅电极和铂对电极的光电化学电池，将碘化氢分解为氢和碘，从而将太阳能转化为化学能。在<P^+> -n Si光阳极上涂上一层非常薄（1 nm厚）的铂、钨或钼层，具有良好的透光性，从而显著地稳定了该阳极。光电流在5000 h以上没有衰减，转换效率超过8%。对于在<n^+> -p Si光电阴极上析氢的电池，采用具有n型非晶Si/p型晶Si异质结结构的新型电极，获得了10.8%的非常高的转换效率。这个数值是迄今为止报道的太阳能直接转化为化学物质的最高数值。控制光电化学电池转换效率的主要因素有：(1)欧姆电阻；(2)电解液对光的吸收；(3)电极上电流密度的不均匀性。研究发现，将大电极细分成小电极，电流密度分布均匀，欧姆电阻小。考虑到这些影响，确定了组件的最佳几何形状，并给出了由这些组件组成的光电电池的设计方法。

The decomposition of hydrogen iodide into hydrogen and iodine by use of a photoelectrochemical cell, equipped with a metal-coated p-n junction silicon electrode and a platinum counterelectrode, has been studied for the purpose of the conversion of solar energy into chemical energy. The <P^+> -n Si photoanode was remarkably stabilized by coating with a very thin (1-nm thick) platinum, tungsten or molybdenum layer having good light trasparency. The photocurrent showed no decay for more than 5000 h and the conversion efficiency exceeded 8 %. For the case of cells in which hydrogen is evolved on the <n^+> -p Si photocathode, a very high conversion efficiency of 10.8 % was obtained by using a new-type electrode having an n-type amorphous Si/p-type crystalline Si heterojunction structure. This value is the highest so far reported as to the direct solar-to chemical conversion.The main factors controlling the conversion efficiency of a photoelectrochemical cell are: (1) ohmic resistance, (2) absortion of light by electrolyte, and (3) nonuniformity of current density on an electrode. It has been found that subdivision of a large electrode into smaller ones makes the current density distribution uniform and the ohmic resistance small. Taking account of these effects, the optimal geometry of a module has been determined, and the method of design of photoelectrochemical cells composed of these modules has been given.