| In the process of the current energy supply, hydrogen as the most promising energy provides clean energy and has the advantages of environmental, easy to store and higher energy density. Electrocatalytic hydrogen evolution reaction(HER) has been regarded as an efficient and promising strategy, which is an available preparation for hydrogen to face the future energy crisis. Therefore, designing with high activity and low cost of electrocatalysts for HER is indispensable. Noble metal catalysts have good catalytic effect for HER. The tradition of noble metal nanoparticles synthesis method is chemical liquid phase reduction, which can’t dispense with the extra addition of additives. In this thesis, noble metal nanoparticles modified silicon nanowires(Ru, Rh, Pt) were prepared by directly reducing noble metal ions with Si-H bonds, which were evaluated as electrocatalysts for HER. Silicon nanowires disperse metal nanoparticles well, which are reduced in abundance by Si-H bonds. The thesis mainly includes the following three parts:(a) Ru ions were reduced with Si-H bonds and attached as nanoparticles to Si NWs to form the Ru/Si NW composites. The obtained composites were characterized by XRD, SEM and TEM. Thus the electrocatalytic activity of the composites was investigated by studying the electrochemical HER performance in 0.5 M H2SO4, which demonstrated good electrochemical performance in HER with small onset overpotential(110 m V) and large cathodic currents and excellent stability. It was noted that the performance of composites are better than that of the pure Ru particles.(b) Rh/Si NW composites were synthesized in the same way of reducing Rh3+ ions with Si-H bonds for electrocatalysts in HER. The results showed the cathodic current of 29.1 wt% Rh/Si NW composites with increasing overpotentials was much stronger than that of the commercial 40 wt% Pt/C. Meanwhile the composites owned small Tafel slope, 24 m V/dec and excellent stability. Composites may have synergistic effect, namely, the absorption sites and the desorption sites, speeding up the rate of hydrogen evolution reaction. DFT simulation also comfirmed that the Rh/Si NW catalysts was modeled with two different reaction surface and two sites of activation barrier. When a Si surface atom is terminated with a hydroxyl(or in other words, poisoned by a hydroxyl), a Rh-adsorbed hydrogen may react with the hydroxyl to regenerate the Si atom by producing water molecules. Then the long-term lifetime of Rh/Si NW catalysts is supported by their self-regeneration ability.(c) Platinum is a precious metal, chemical property is stable, not easy to be oxidized in the air, and it has good catalytic effect. Platinum can be as a good catalyst in isomerization, cyclization, hydrogenation, dehydrogenation and dehydration, oxidation, cracking, etc. In the same synthesis way, platinum nanoparticles modified silicon nanowires composites(Pt/Si NW) have been prepared and were applied to electrochemical hydrogen evolution test, having good electrochemical performance. The XRD pattern of Pt/Si NW composites was also shown that all the diffraction peaks could be well indexed as Pt(111),(200),(220),(311) and(222); Si(111) and(311), respectively. The structure details were studied by TEM, showing Si NWs were wrapped by uniform Pt nanoparticles. It was noted that the onset overpotential was closing to 0 V and the Tafel slope was 26 m V/dec. In addition, Pt/Si NW composites also showed good stability in acidic medium after 1000 cycles test. |
PDF Full Text Request