Synthesis, Characterization And Electrocatalytic Performance Of Pd/CMK-3for Formic Acid Oxidation

The problems of energy sources and environment have atracted more and more attention with the development of economy. Traditional fossil fuel is limited, and the energy conversion efficiency of that is very low. Especially, it will probably cause serious threatens in the process of transport and use. As a result, new types of clean energy such as fuel cell are developed. And because of its high energy conversion efficiency, small environmental impact and multiple sources, direct formic acid fuel cell (DFAFC) gradually becomes one of the research highlights in the academic world.Recently, the DFAFC studies have been focused on exploring highly catalytic activity anodic catalysts. It can be seen that formic acid electrooxidation occers mainly through the dehydrogenation path on Pd compared with Pt, so the cost-efficient Pd catalyst possesses stronger poisoning-resistant ability. Thus, Pd is a promising catalyst for formic acid oxidation. In addition, the catalytic activity is closely related to the catalyst support. Because of the uniform mesoporous pore structure, large specific surface area and tunable pore size, ordered CMK-3has been widely used not only in traditional catalytic field but also in electrochemical research.In this study, mesoporous silica SBA-15was prepared via hydrothermal reation. Then ordered mesoporous carbon CMK-3was implemented using SBA-15as the hard template and sucrose as the carbon source. After that, palladium supported on CMK-3(Pd/CMK-3) with a loading (ca.20wt%Pd) was synthesized through a complexing reduction process. In order to explore the essential properties of the as-synthesized materials, the relevant materials were characterized by XRD, TEM, Raman spectra and pore size distribution measurement, etc. The electrochemical activity of as-prepared catalysts for formic acid was discussed deeply by changing the factors of scanning rate, catalyst support, hydrothermal temperature and reaction time.The results showed that a series of CMK-3were prepared by SBA-15successfully, and the p6mm hexagonal symmetric pore structure of CMK-3was highly ordered. The BET specific surface area of CMK-3was larger than activated carbon (AC), and the pore size and pore volume gradually increased with the improvement of temperature. Complexing reduction method realized the load of Pd on the support of CMK-3, and the Pd nanoparticles with the average size of4.0to4.5nm were well dispersed on CMK-3surfaces. Moreover, mesoporous carbon CMK-3showed more complete graphitization and more excellent electroconductibility than activated carbon, which was highly critical to electrocatalytic experiment.Compared with other carbon materials, CMK-3possessed higher electric conductivity and larger specific surface area, and had lots of uniform mesoporous structure. Furthermore, relatively larger pore size of CMK-3was advantageous for Pd nanoparticles to enter into the materials. So less Pd on the CMK-3surface led to smaller size of Pd particles. For these given reasons, Pd/CMK-3catalyst exhibited more outstanding electrochemical performance than other catalysts.Hydrothermal temperature had complicated impacts on catalytic activity. On the one hand, larger pore size of CMK-3with the higher hydrothermal temperature resulted in better dispersion of Pd particles. And it would increase the catalytic activity. On the other hand, the ordering of CMK-3structure decreased with the increase of the hydrothermal temperature. And CMK-3could not maintain the uniform p6mm hexagonal symmetric pore structure when the temperature reached150℃. So it was disadvantageous to the catalytic activity. According to the above two contradictory impacts, the catalytic activity increased rapidly when temperature came to100℃. Then the peak current almost remained the same. At last, the electrocatalytic activity declined sharply at150℃.The surface of Pd/CMK-3and Pd/AC adsorbed a mass of poisonous species after a considerable time. In addition, the size of Pd nanoparticles was nearly identical for Pd/CMK-3and Pd/AC. Consequently, the stability of Pd/CMK-3and Pd/AC was nearly completely equivalent when continuously testing over100seconds. So the poisoning-resistant ability of Pd/CMK-3for formic acid oxidation should be improved further.In conclusion, the research revealed that Pd catalysts supported on CMK-3exhibited excellent catalytic activity for formic acid oxidation. The pore size and ordering of CMK-3exerted significant influence on activity. Accordingly, Pd/CMK-3may have potential application value after researchers improve its stability.