Preparation Of Cobalt Based DBFC Anode Materials And The Study Of Their Electrochemical Behavior

Fuel cell is a new energy device that directly converts chemical energy from fuel and oxidizer into electrical energy,and has a broad application prospect.Among them,direct borohydride fuel cell（DBFC）,which uses sodium borohydride（Na BH₄）directly as the fuel in the anode area,has the advantages of cleanliness,high efficiency,small size and fast start-up and so on.The characteristics of the electrode material is the critical factor in the determination of DBFC performance.The research on electrode materials with high performance has received a lot of attention from researchers.Currently,noble metal-based catalysts show good catalytic activity for the electrooxidation of borohydride,but their resources are scarce,and the price is expensive.In this paper,porous nickel foam（Ni Foam,NF）is used as a support to load transition metal of cobalt（Co based materials）to catalyze the electrooxidation reaction of sodium borohydride（Na BH₄）,and the electrocatalytic properties of the as-prepared materials were studied.In addition,carbon paper-loaded lead（Pb）based materials were prepared and applied to catalyze the electroreduction reaction of maleic acid（C₄H₄O₄）.The Co based and Pb based materials were used as the anode and cathode,respectively,and a mixture of Na BH₄ and sodium hydroxide（Na OH）was used as the reaction solution in the anode region,and a mixture of C₄H₄O₄ and sulfuric acid（H₂SO₄）was used as the reaction solution in the cathode region to assemble a new direct sodium borohydride-maleic acid fuel cell（DBMAFC）,and then the cell characteristics were studied.The main research contents are as follows:A highly efficient Ni C₂O₄-supported Co-Mo complex electrode（Co Mo@Ni C₂O₄/NF）with complex structure and composition was obtained by successfully loading nickel oxalate（Ni C₂O₄）with a flower-like structure composed of nanosheets on the surface of NF through electrodeposition and chemical etching processes,and then cobalt-molybdenum（Co-Mo）composites were co-deposited on its surface,and its characteristics of catalytic Na BH₄electrooxidation reaction in alkaline environment were investigated.In a mixed solution with Na OH concentration of 1.0 mol dm^-3 and Na BH₄ concentration of 0.1 mol dm^-3,Co Mo@Ni C₂O₄/NF electrode catalyzed electrooxidation of Na BH₄ produced current density of up to 199.34 m A cm^-2（-0.52 V）.The electrochemical active surface area of this electrode is299 cm²,and the number of electrons transferred in the catalytic Na BH₄ electrooxidation reaction is 7.5,electrocatalytic reaction has an activation energy of 16.86 k J mol^-1.The flaky Co was loaded on NF by electrodeposition,and then the composition and structure of the loaded Co were adjusted and controlled by etching with oxalic acid（H₂C₂O₄）to obtain Co C₂O₄ with nanorod-like structure,and finally the metallic Co with predominantly tiny flaky structure was reduced using Na BH₄.Thus,a Co based composite electrode（Co/NF-Co C₂O₄-Co）containing various substances such as Co,Co C₂O₄ and oxides of Co was produced for catalytic Na BH₄ electrooxidation reaction.The as-prepared electrode has a 3-dimensional（3D）nanoflower-like structure for porosity,which provides for an abundant supply of catalytically active sites in the electrochemical reaction,and the synergistic effect of various components in the electrode can effectively improve its electrocatalytic activity.In addition,the metal Co in the as-prepared electrode can provide a fast electron transfer pathway during the electrochemical reaction.The surface of Co/NF-Co C₂O₄-Co electrode generated an oxidation current density of 315.85 m A cm^-2 at-0.58 V in the mixing solution of Na OH concentration of1.0 mol dm^-3 and Na BH₄ concentration of 0.1 mol dm^-3,which is significantly higher than that of Co/NF-Co C₂O₄(264.55 m A cm^-2)and Co/NF(59.96 m A cm^-2).It is very worth to note that the Co/NF-Co C₂O₄-Co was further applied in a cylindrical rotating bed（CRB）to weaken bubble effect and enhance mass transfer during the electrooxidation of Na BH₄.The results demonstrate that the device can significantly improve the electrochemical performance,which is 2.7(electrode rotational speed of 112 r min^-1)and 3.9(solution circulating flow rate of 400ml min^-1)times higher than the traditional stationary state at the potential of-0.2 V in mixed solution with Na OH concentration of 1.0 mol dm^-3 and Na BH₄ concentration of 0.01 mol dm^-3,respectively.Pb based materials（Pb/CP）with nanoflower-like structures were successfully loaded on the CP surface by chrono amperometry fast method and applied to catalyze the electroreduction reaction of C₄H₄O₄ in an acidic environment.The reduction current density reached 232.78 m A cm^-2 with the potential of-1.0 V in a mixed solution of H₂SO₄ concentration of 1.0 mol dm^-3and C₄H₄O₄ concentration of 0.2 mol dm^-3.The as-prepared Co Mo@Ni C₂O₄/NF and Co/NF-Co C₂O₄-Co electrodes were used as the anode and Pb/CP as the cathode,respectively,a mixture of Na OH concentration of 1.0 mol dm^-3 and Na BH₄ concentration of 0.5 mol dm^-3 was used as the anode reaction solution,a mixture of H₂SO₄ concentration of 1.0 mol dm^-3 and C₄H₄O₄ with a concentration of 0.2 mol dm^-3 was used as the cathodic reaction solution to assemble DBMAFC separately,where the highest power densities were 25.63 m W cm^-2 and 32.51 m W cm^-2 at the reaction fluid flow rate of 5 ml min^-1,respectively,both of which exhibited good stability.The purity of succinic acid（C₄H₆O₄）in the cathode reaction products of the cell were up to 97%.