Development of the Photoelectrolysis Cell for Energy Storage Using Silicon Electrode

为了将太阳能转化为化学能，研究了利用光电化学电池将碘化氢分解为氢和碘。该电池配有金属涂覆的p-n结硅电极和铂对电极。通过在具有良好透光性的非常薄(1 nm厚)的铂、钨或钼表面涂覆一层膜，可以显著地稳定P^+&n Si光阳极。光电流在5000h以上没有衰减，转换效率超过8%。对于在-lt；n^+-p-Si光电阴极上析氢的电池，采用n型非晶硅/p-型晶体硅异质结结构的新型电极，获得了10.8%的很高的转换效率。控制光电化学电池转换效率的主要因素是：(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。研究发现，将大电极细分为小电极，可使电流密度分布均匀，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化学电池的设计方法。

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.