Electrocatalysis of Borohydride Oxidation on Colloidal Pt and Pt-Alloys (Pt-Ir, Pt-Ni, and Pt-Au) and Application for Direct Borohydride Fuel Cell Anodes

Abstract

Colloidal Pt and Pt-alloys ͑Pt-Au, Pt-Ni, and Pt-Ir, 1:1 atomic ratio͒ supported on Vulcan XC-72 ͑20% wt metal load͒ were prepared according to the Bönneman method and investigated for electrocatalytic activity with respect to borohydride oxidation for fuel cell applications. Voltammetry on static and rotating electrodes, chronopotentiometry, and chronoamperometry were performed on the colloidal catalysts immobilized on glassy carbon with the help of Nafion 117. The BH 4 − electro-oxidation mechanism is complex and it could involve, depending on the catalyst, a number of species such as BH 4 − directly, BH 3 OH − , and H 2 ͑the latter two species formed in catalytic hydrolysis͒. Direct borohydride fuel cell experiments using a 2 M NaOH-2 M NaBH 4 solution on the anode side, 5 mg cm −2 colloidal anode catalyst load, Nafion 117 membrane, and an O 2 gas diffusion cathode with 4 mg cm −2 Pt, showed that Pt-Ir and Pt-Ni were the most active anode catalysts, giving a cell voltage of 0.53 V at 100 mA cm −2 and 333 K.

Pd–Ir alloy as an anode material for borohydride oxidation

“…The free energy of adsorption of borohydride ions on the Pd 2 eIr 1 (111) and Pd 2 eIr 2 (111) surfaces can be calculated using Equations (8) and (9): (9) where G BH À 4;aq is the free energy of the borohydride ions in aqueous solution [15], G * is the free energy of the bare surface, G BH * 3 þH * is the free energy of the dissociatively adsorbed borohydride species,…”

“…Kiran et al, [13] increased the power density of a DBFC by 35% by using an IreRh alloy supported on carbon compared to a carbon supported Rh anode. It might be possible to increase the activity of pure Pd by alloying it with Ir, as it was observed by Gyenge et al, [8] and Kiran et al, [13] for the addition of Ir to Pt and Rh to form PteIr and RheIr alloys, respectively. In this work, cyclic voltammetry was performed to analyze the oxidation peaks and current densities of borohydride oxidation on a PdeIr alloy anode.…”

“…The use of PteIr and PteNi catalysts gave the same power density of 53 mW cm À2 at 75 C, showing the most active catalytic activity among all the catalyst being tested. When PteIr was used, the oxidation peaks were shifted to more negative potentials than those observed with PteNi, suggesting the potentially favorable kinetics on PteIr alloy and yielding the highest voltammetric BH 4 À oxidation current densities [8]. Kiran et al, [13] increased the power density of a DBFC by 35% by using an IreRh alloy supported on carbon compared to a carbon supported Rh anode.…”

“…Although Pd-based alloys have not been tested, alloying electrodes such as Pt, Ag or Au with other materials has improved the performance of the DBFC. Gyenge et al, [8] obtained higher peak currents and more negative borohydride oxidation potentials by using a PteAu alloy instead of pure Pt. Alloys such as PteIr and PteNi were also tested as working electrodes for a DBFC [8].…”

“…Gyenge et al, [8] obtained higher peak currents and more negative borohydride oxidation potentials by using a PteAu alloy instead of pure Pt. Alloys such as PteIr and PteNi were also tested as working electrodes for a DBFC [8]. The anolyte solutions contained 2 mol dm À3 NaBH 4 in 2 mol dm…”