Partial inhibition of borohydride hydrolysis using porous activated carbon as an effective method to improve the electrocatalytic activity of the DBFC anode

Abstract

Carbon materials are commonly used catalyst supports in various types of fuel cells. Due to the possibility of designing their properties, they seem to be attractive and functional additives. In Direct Borohydride Fuel Cells (DBFCs), the electrooxidation reaction of borohydride competes with the undesirable hydrolysis reaction, therefore our work aimed to modify anodes based on a multi-component hydrogen storage alloy with a small number of activated carbons obtained from coffee waste to improve the hydrogen electrosorption properties. The produced activated carbons differed in terms of their physicochemical properties due to the different coffee waste-to-KOH ratio (1 : 1–1 : 4). Pressure measurements confirmed their effectiveness in relation to unconsumed hydrogen release, which initially hindered fuel diffusion. Nevertheless, it has been established that the addition of activated carbons improved the electrocatalytic activity of the anode, especially during cyclic operation (coulombic efficiency increased from 23% to 44% of the theoretical value). Moreover, X-ray photoelectron spectroscopy revealed that borohydride as a known reducing agent caused the reduction of oxygen functional groups on the carbon surface during DBFC operation, which made it possible to eliminate one of the factors influencing the BOR characteristics, and thus a more precise comparison of the analyzed activated carbons.