The Preparation And Properties Of Molybdenum Carbide For Hydrogen Evolution Reaction And The In Situ Infrared Spectroscopy Of Ethanol Electrooxidation

(1)Molybdenum carbide is regarded as an excellent substitute for Pt-based catalysts to be employed in hydrogen evolution reaction?HER?given its inexpensive cost,superior catalytic performance and long-term stability.In this work,salt sealed molybdenum carbide was prepared by using sodium molybdate and 2,6-diaminopyridine as the reactive raw materials,followed by continuous operation of salt sealing and calcining the precursor under an inert atmosphere.The composition and structure of salt sealed molybdenum carbide were determined by Energy-dispersive X-ray spectroscopy?EDS?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The results indicate that the product belongs to orthorhombic crystal system Mo2C with molybdenum oxides on the surface,which may originate from surface oxidation.Taking into account the results of XPS and turnover frequency calculation,we can summarize that the formation of pores via salt sealing contributes to expose more active sites,while also enlarges the contact area with oxygen at the same time,resulting in a higher content of molybdenum oxide.In general,the enriched nanoporosity with more exposed active sites and larger surface area pave the way for enhanced HER activity with an overpotential of 175 mV to achieve a current density of 10 mA cm-2.The Tafel slope of Mo2C with salt sealing is 88 mV/dec,which can be considered as the proof of Volmer-Heyrovesy mechanism with the electrochemical desorption as the rate-determining step.?2?Direct ethanol fuel cell is considered as a promising energy conversion device due to its high energy density,moderate operating conditions and environment friendliness.In addition,direct ethanol fuel cell is a green energy source,since ethanol is not toxic,and it can be produced by the fermentation of biomass,therefore it is a completely renewable resource.Since the CO poisoning effect on Pd catalyst is rather smaller,therefore Pd catalyst was obtained by the method of electrodeposition at a constant potential in this work to study the electrocatalytic mechanism of ethanol oxidation.The apparent activation energy for the electrooxidation reaction of ethanol was obtained by CV curves at different temperatures.The obtained value at-0.13V was 16.03KJ/mol according to Arrhenius formula.After that,in situ infrared spectroscopy of ethanol electrooxidation at different temperatures on the surface of Pd catalyst was carried out.The results suggest that as the temperature increases,the selectivity for the complete oxidation of ethanol to CO₂ showed a noticeable improvement.The selectivity at 55° was three times higher than that of 25?.In the end,the zinc selenide window tablet was adopted at room temperature to obtain in situ infrared spectroscopy of ethanol electrooxidation.And the characteristic peak at 933cm-1 assigned to acetaldehyde was successfully observed,therefore the electrooxidation mechanism of ethanol on Pd electrode was preliminarily speculated.Combined with the results of quantitative calculation,a conclusion can be drawn that the:intermediate of the reaction was preferable to adopt the adsorption mode of double-carbon coadsorption at higher temperature.In other words,higher temperature is beneficial to the cleavage of the C-C bond in ethanol,therefore the selectivity of the complete oxidation of ethanol to CO₂ via 12 electron transfer process was significantly increased at high temperature.