Correlation between partial inhibition of hydrogen evolution using thiourea and catalytic activity of AB5-type hydrogen storage alloy towards borohydride electrooxidation

Direct borohydride fuel cells (DBFCs) are devices which directly convert the chemical energy stored in the borohydride ion and oxidant into electrical energy as a result of redox reactions. Unfortunately, a significant amount of fuel is lost as a result of the undesirable hydrolysis reaction. The selection of an efficient borohydride hydrolysis inhibitor requires detailed knowledge regarding the interaction mechanism between the inhibitor molecule and electrode surface. In this study, various amounts of thiourea additives (0.011–1.600 mM) were tested to select the best fuel composition for DBFC application. When AB5-type anode was used, only partial inhibition of sodium borohydride hydrolysis was a desirable phenomenon. Partially released hydrogen results in the improvement of catalytic properties of the alloy. The addition of 0.016 mM thiourea does not inhibit the oxidation of borohydride, on the contrary, it increases the practical capacity from 27% to 41% of the theoretical value. Moreover, we indicate that the addition of thiourea prevents corrosion as well as degradation of the electrode surface. Pressure measurements confirmed the effectiveness of thiourea in relation to hydrogen evolution, while X-ray photoelectron spectroscopy and Raman spectroscopy revealed that the electrode surface was not poisoned.