Tunable hydrogen generation from sodium borohydride with silicon carbonitride functionalized carbon nanostructure electrode

A novel multilayer carbon nanostructure catalyst (MCNC), composed of carbon fiber (CF), carbon nanotube (CNT), precious metal dispersions (Pt/Pd/Ru) and silicon carbonitride (SiCN) layer derived from a liquid based polymeric precursor, has been developed in this work with the aim to be used as the electrode for decomposing water into hydrogen. The ternary Pt/Pd/Ru catalysts are deposited on the thin film coating of SiCN functionalized carbon nanotube (SiCN/CNT) electrophoretically deposited (EPD) on carbon fiber. The silicon carbonitride layer makes the silicon-transition metal bond form a sub-nanometric layer of metal catalyst to increase the surface-to-volume ratio and catalytic efficiency. Sodium borohydride, NaBH4, solution spontaneously reacts with MCNC to generate hydrogen in a very fast rate, depending on its concentrations. The ternary catalyst shows a higher generation rate compared to the binary and single catalytic systems already prepared with the same synthetic procedure. The reaction mechanism and the catalytic efficiency have been described in terms of the reaction pattern that involves an electric charge transfer, due to the negative charge on the BH4 ion transferred with one hydrogen atom via SiCN/CNT structure, ensuring the generation rate increase. As an electrical potential is applied between two MCNC electrodes in sodium borohydride electrolyte, the generation rate of hydrogen can be tuned by the applied potential. When the concentration of NaBH4 is much diluted, this electrolytic and hydrolytic reaction obeys the Faraday's law. Due to diluted solution, the reaction of hydrogen generation is dominated by electrolytic reaction that can be decomposed at a very low potential ~0.5 V. This result indicates that the band gap of the semiconductive MCNC electrode can be lowered by the applied potential. The figure-of-merit, FOM can reach 1150 Lmin1 [NaBH4]1gmet 1 , as one volt applied. When a constant voltage applied, FOM gradually decreases with [NaBH4] increase till to reach the steady state that the zero order reaction is achieved. The MCNC electrode is robust and re-useable by alcohol rinsing and dry after reaction.