Non-platinum Catalysts For Direct Alcohol Fuel Cells And Electrode Reactions For Water Electrolysis For Hydrogen Production

All activities of human society are inseparable from energy.In recent decades,massive population growth and rapid industrial development have aggravated the consumption of traditional fossil fuels such as coal,oil and natural gas,resulting in the rapid depletion of them and severe environmental pollution problems.Therefore,development of renewable clean energy becomes more and more important and urgent.Direct alcohol fuel cell(DAFC)is a kind of new energy conversion device that can directly convert chemical energy into electric energy.Generally,the fuels of DAFC are organic small molecular alcohols such as methanol and ethanol,which have been regarded as the ideal fuels due to their low price and wide source.The above advantages make DAFC have promising applications in the field of energy sources.In addition,as a kind of clean,renewable and highly efficient non-carbon energy,hydrogen energy has been the permanent strategic option of maintaining the energy supply.Among the different methods of hydrogen production,electrolytic water splitting technique has been widely adopted due to its easily obtained raw materials and high-purity products.Since the kinetics of the methanol/ethanol oxidation reactions(MOR and EOR)and oxygen reduction reaction(ORR)of DAFC,and the oxygen evolution reaction(EOR)and hydrogen evolution reaction(HER)of water electrolysis are sluggish,all of them need efficient electrocatalysts to accelerate the reactions.Especially for the MOR/EOR,ORR and HER,the widely accepted efficient catalysts are still Pt-based catalysts.However,the high price and poor reserves limit their commercial development and large-scale applications.Therefore,development of cheap and high-performance catalysts is the focus of current research.In this paper,three series of non-Pt materials were prepared through co-reduction or hydrothermal methods.The catalytic performance of them for alcohol oxidation,ORR and HER are investigated.Related effects on the catalytic performance are also discussed,aiming to reduce the reliance on the Pt-based catalysts.Specific contents are as follows:1.A series of Pd_mAg/C alloy electrocatalysts for EOR and MOR were synthesized via a simple liquid phase co-reduction method with silver nitrate and potassium chloride palladionate as the precursors and sodium borohydride as the reducing agent.Pd and Pt were in the same group of the Periodic Table and similar in nature,whereas the price of Pd is much lower than Pt,which makes Pd a good substitute for Pt.It was found that the catalytic performance of the Pd_mAg/C electrocatalysts was related to m(m refers to the atomic Pd/Ag ratio),and Pd_0.5Ag/C catalyst had the highest performance among the Pd_mAg/C catalysts.The peak currents of EOR and MOR are8.688 and 2.475 m A(?)g_Pd^-1,respectively,which are 2.18 and 1.42 times that of Pd/C catalyst.In addition,the catalytic activity of Pd_mAg/C electrocatalysts was closely related to the potential range of the CV curves.When Pd_0.5Ag/C was tested in a relatively wide potential scope(-1.0?0.5V),the peak currents of EOR and MOR are ca.9.39 and 3.67 times higher than that tested in the narrow potential scope(-1.0?0.1 V),respectively.This was because the silver oxide formed under high potential(0.5 V)has an obvious promotion effect on the rapid removal of carbon containing intermediate species from the surface of the adjacent Pd atoms.Our findings suggest that the addition of silver can not only improve the catalytic performance of the Pd catalyst,but also reduce the cost of the Pd-based bimetallic catalysts.2.A series of Fe_xNC catalysts were successfully prepared through high-temperature pyrolysis with iron nitrate,glucose and melamine as the Fe,C and N sources,respectively.The composition and morphology of the catalysts were analyzed by means of XRD,TEM and XPS,and the catalytic properties of the catalysts for ORR in alkaline media were tested by various electrochemical techniques including CV,LSV and EIS.The effects of the pyrolysis temperature,pyrolysis time and the amount of iron nitrate on the catalytic performance are comprehensively investigated.Fe_0.50NC-800-1h catalyst,which was prepared by adding 0.50 g ferric nitrate and pyrolyzed at 800?for 1h,had the best catalytic performance.The initial potential of ORR was about 956 m V in 0.1 M KOH solution,and the half-wave potential was found at ca.812 m V,which was 43 m V lower than that on commercial Pt/C catalyst.In addition,Fe_0.50NC-800-1h catalyst could exhibit good catalytic stability and methanol tolerance.After 1000 cycles of repeated cyclic voltammetry scanning,the half-wave potential of ORR shifted negatively only by 9 m V.In the presence of methanol,the current decay in the chronoamperometric response at 1000 s is only9.9%,and also much lower than that on Pt/C catalyst(46.6%).3.The cobalt,iron carbonate hydroxide(CoFe(OH)_x(CO₃)_y)nanorod array was in-situ prepared on the surface of nickel foam(NF)by hydrothermal synthesis method with cobalt nitrate and iron nitrate as the precursors.Fe-Co P/NF catalyst was then prepared through the phosphating of CoFe(OH)_x(CO₃)_y with sodium hypophosphate as the phosphorus source.The experimental conditions such as the amount of sodium hypophosphate,phosphating time and phosphating temperature were optimized.Results show that the Fe-Co P/NF catalyst did not show superior catalytic activity for HER under small current densities as compared with Pt-C/NF catalyst,in terms of the lower initial HER potential and larger overpotential.However,with increasing the current density,the Fe-Co P/NF catalyst exhibited excellent catalytic performance for HER with the overpotential of only 185 m V at 300 m A cm^-2,which was much lower than that on Co P/NF(?₃₀₀=222.6 m V)and Pt-C/NF catalyst(?₃₀₀=240.4 m V).The low Tafel slope and charge transfer resistance suggest the fast kinetics of HER.In addition,after 1000 cycles of repeated cyclic voltammetry scanning,the catalyst did not show any significant attenuation of the catalytic activity,exhibiting a high stability.The increased electrochemical active surface area and conductivity are responsible for the enhancement in the catalytic performance of the Fe-CoP/NF catalyst.