Investigation Of Non-noble Metal Catalysts For Direct Borohydride Fuel Cell

Direct borohydride fuel cell?DBFC?,which is consisted of alkaline aqueous solution of borohydride as fuel,has achieved extensively attention for many advantages,such as high power density,specific capacity and cell voltage.Theoretically,the direct electro-oxidation of per molecular borohydride at anode can transfer eight electrons.However,in fact,the hydrogen is easily generated by the borohydride hydrolysis,which not only decreases the efficiency of the battery but generates bubbles that hinder the transmission of ions and make it difficult to design the structure of the battery.Therefore,it is very important to develop the anodic catalysts with high catalytic activity,low cost and the ability to inhibit hydrolysis of borohydride.Co-based compounds have attracted attention due to their unique catalytic properties and low cost.As a typical Co-based compound,Co₃O₄ has a large specific surface area and has been used in the field of lithium-ion batteries.However,there are no report on the use of the DBFC anode catalyst.So,Co₃O₄ was used in this paper as the DBFC anode catalyst and the hydrolysis of borohydride was inhibited by silver plating.In addition,based on previous research results,graphene quantum dots?GQDs?were doped with poly?3,4-ethylenedioxythiophene??PEDOT?to improve the catalytic effect of PEDOT on oxygen reduction reaction.The specific research contents are as follows:?1?Co₃O₄ was obtained by sol-gel method using CoCl₂·6H₂O,Co?NO₃?₂·6H₂O and Co?Ac?₂·4H₂O as raw materials respectively,and the effects of cobalt source on the catalytic performance of Co₃O₄ were studied by electrochemical methods and cell tests.The results show that the different cobalt source does not affect the structure of Co₃O₄,but will affect the morphology.The Co₃O₄ prepared from Co?NO₃?₂·6H₂O showed the best catalytic activity and the highest power density of the battery was 62 m W·cm-2.The Co₃O₄ prepared from CoCl₂·6H₂O had the highest electron transfer number of 7.06,which closes to the theoretical value of 8,and the specific capacity of the battery was 735 m Ah·g-1.But,due to the hydrolysis reaction,the specific capacity of the battery is much lower than the theoretical specific capacity?5.7 Ah·g-1??2?Co₃O₄@Ag was prepared by silver mirror reaction.The electrocatalytic properties of two catalysts and the inhibition of borohydride hydrolysis were studied systematically.The results indicate that the grain size of Co₃O₄ after silver plating has increased.Electrochemical tests show that there was synergistic catalysis between Co₃O₄ and Ag.Co₃O₄@Ag showed better electrocatalytic activity and stability.The highest power density and specific capacity of the assembled cell were 55 m W·cm-2 and 971 m Ah·g-1.The increase of specific capacity shows that the utilization efficiency of the fuel is improved,that is,silver plating can effectively inhibit the hydrolysis of borohydride.Co₃O₄@Ag shows a good application prospect in DBFC.?3?CoSO₄·7H₂O and SnSO₄ were used as raw materials to prepare Cox-Sn bimetallic catalysts on the nickel foam and the catalytic effect of this type of catalyst on the electro-oxidation of KBH4 was systematically studied.The results show that the Co3-Sn bimetallic catalyst is spherical with a size distribution of 10-30 nm.Electrochemical tests and fuel cell tests indicate that the catalytic performance of the catalyst increases with the increase of Co relative content,while Sn can inhibit the hydrolysis of KBH4.The maximum power density of the DBFC catalyzed by Co3-Sn/Ni-foam was 158 m W·cm-2.The discharge tests show that the specific capacity of DBFC decreases with the increase of Co relative content,but increases with the increase of discharge current.This result shows that there is also a hydrolysis of borohydride which is not related to the performance of the catalyst.Only by increasing the reaction rate can it be relatively inhibited.?4?GQDs were prepared by hydrothermal method using graphene oxide as raw material.The electropolymerization was used to dope PEDOT with GQDs to prepare GQDs@PEDOT,which was used as catalyst for the oxygen reduction reaction?ORR?.The reaction mechanism of ORR and catalytic activity of GQDs@PEDOT were investigated systematically.The results show that the addition of GQDs not only provided an anchoring point for PEDOT,but enhanced the interaction of PEDOT with O2 by weakening O2 adsorption energy.Calculated by the K-L equation,the maximum electron-transfer number of ORR after doping increased from 2.66 to 3.57,which is close to the theoretical value.At the same time,the stability of the catalyst also had been improved.