Research On The Direct Dimethyl Ether Fuel Cell

Dimethyl ether(DME) with the formula CH₃OCH₃ is a non-toxic organic compound soluble in water.Gaseous DME can be easily pressurized into liquid under 0.6 MPa at room temperature for storage and distribution.DME without C-C bond can be almost completely electrooxidized to CO₂.One mole of DME can release 12 electrons.Due to favorable physical properties of DME as a fuel and its high theoretical energy density of 8.2 kWh kg^-1,DME is regarded as a promising alternative fuel to hydrogen used in proton exchange membrane fuel cell(PEMFC). Since direct dimethyl ether fuel cell(DDFC) has a relatively high theoretical energy conversion efficiency(95%) with less energy loss than direct methanol fuel cell (DMFC) due to fuel crossover,it is believed that the DDFC could be a valuable direct liquid fuel cell candidate for commercialization.The surface composition,microstructure of Pt/C and Pt-Ru/C catalysts were characterized by typical material identification methods such as powder X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy.Electrooxidation behavior of DME was systematically investigated by electrochemical analysis methods such as the galvanostatic discharge,cyclic voltammetry etc.It is revealed that the Pt-Ru alloy has a synergistic effect to avoid poisoning from CO.Compared with Pt/C,the use of Pt-Ru/C as the anode catalyst significantly decreases the anode polarization of the DDFC,so that the cell performance is improved.The effectiveness of Ru addition can be further strengthened by using the aqueous solution saturated with DME as the fuel.Electrochemical behavior of DME dissolved in acidic,neutral and alkaline anolyte on Pt-Ru/C catalyst was studied.In alkaline medium,OH species adsorb on Ru at low potentials,which enhances the electrooxidation of intermediate products, thus improve protection of catalytic active site,DME adsorption and oxidation rate on the catalyst.The oxidation peak current of DME in alkaline media can reach up to 120 mA cm^-2,which is much higher than that in acidic medium(20 mA cm^-2).The use of alkaline anolyte saturated with DME as the fuel can effectively improve the performance of the DDFC.The influences of operation temperature,catalyst loadings,NaOH concentration and applied electrolyte membrane on the cell performance are investigated.At 80℃,a maximal power density of 81 mW cm^-2 has been achieved when the DDFC uses Nafion 112 membrane as electrolyte,2M NaOH saturated with DME as the fuel.The use of hydrogen peroxide as the oxidant effectively increases the open circuit voltage of the direct DME/hydrogen peroxide fuel cell(DDHPFC),and greatly enhances fuel cell performance due to that hydrogen peroxide significantly improves the cathode potential and decreases the cathode polarization.The influences of operation temperature,hydrogen peroxide concentration,electrolyte concentration in anolyte and catholyte,and applied electrolyte membrane on the performance of the DDHPFC are investigated.At 80℃,a maximal power density of 265 mW cm^-2 has been achieved when the DDHPFC uses Nafion 112 membrane, 2M NaOH saturated DME as the fuel,which is the best reported performance of the DDFC so far.As an promising alternative fuel,DDFC deserves a more in-depth research and development.