Electrochemically anodized nano-crystalline silicon (nc-Si) layer is one of the self-organized Si nanostructures. In addition to efficient visible luminescence, many specific effects are induced in nc-Si. For instance, a multiple-tunneling electron transport through nc-Si dots interconnected with tunnel oxides leads to the emission of ballistic electrons. This electron emitter operates not only in vacuum but also in atmospheric pressure gases and even in solutions. Following summary on the emission mechanism and characteristics, it is shown here that the emitter acts as an active electrode supplying highly reducing electrons into solutions. No conventional electron emitters are available for this operation mode. In salt solutions, injected ballistic electrons promote reduction of positive ions and subsequent thin film deposition of metals and semiconductors. When driven in aqueous solutions such as water, acid, and alkaline solutions without counter electrodes, in addition, H2 gas is generated with no by-product like O2. Effects of energetic electron injection into water are investigated by voltammogram measurements. The H2 generation is associated with a pH value shift and an increase of H2 content. The mechanism of direct H2 generation is discussed in relation to the preferential reduction of H+ ions, including its technological potential.
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