A parametric study of a platinum ruthenium anode in a direct borohydride fuel cell

Abstract

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt-Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm -2 using ambient oxygen and air cathodes respectively at medium temperatures (60°C). The performance of the DBFC is very good at low temperatures (ca. 30°C) using modest catalyst loadings of 1 mg cm -2 for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times.

Developments in direct borohydride fuel cells and remaining challenges

“…In the absence of TU, three oxidation peaks were observed: the peak a 1 is due to oxidation of the hydrogen generated through the hydrolysis of borohydride (reactions (13) and (14)); the peak a 2 is due to the direct oxidation of BH 4 À (reaction (2)); and the third peak in the reverse cycle, c 1 (not shown for clarity), is due to the intermediate product of oxidation, BH 3 OH À (reaction (12)). In the presence of TU it was observed that the peaks a 1 and c 1 disappear, which means that TU inhibits the oxidation of H 2 and possibly the catalytic hydrolysis of BH 4 À in conjunction with the oxidation of the intermediate species (reactions (11) and (12) do not take place in this case). Only an oxidation peak at the same potential as the oxidation of BH 4 À on Pt (À0.2 V vs. Ag/AgCl) appears.…”

“…The anode of a DBFC typically operates at a mixed potential due to the competition between anodic borohydride oxidation and, at the OCP, cathodic water reduction, which is thermodynamically favoured. A mixed potential can also be established at the cathode under low current conditions due to the crossover of borohydride fuel [10,11]. These effects, particularly the mixed anode potential, lead to an OCP that is considerably lower that the theoretical value.…”

“…Both, PteIr and PteNi gave the highest cell potentials at any given current density, e.g., at 100 mA cm À2 and 333 k the cell potential was 0.53 V vs. MMO with an anode catalyst loading of 5 mg cm À2 in the anode. Duteanu et al [11] reported experiments using a binary alloy of Pt and Ru deposited on a carbon anode together with a Pt/C cathode in a MEA. The catalyst loading was 1 mg cm À2 in both cases.…”

The effect of catalyst support on the performance of PtRu in direct borohydride fuel cell anodes

“…It must be noted that a cation exchange membrane (Nafion Ò 117) was employed in the present work. The use of an anion exchange membrane would improve the ionic conductivity and therefore the fuel cell performance [25]. However, anion exchange membranes are typically less robust and more costly.…”

“…It is likely however that direct borohydride electrooxidation also takes place on the Pt. Duteanu et al conducted a parametric study on a PtRu anode for DBFCs and reported power densities of up to 145 mW cm -2 at 333 K with a 1 mg cm -2 PtRu/C anode, a 1 mg cm -2 Pt/C cathode, and an anion exchange membrane [25]. Tsang and Prasad also emphasized the importance of controlling the operating parameters and fuel composition such that the rate of hydrogen formation does not exceed the rate of hydrogen electrooxidation [24].…”