Pt–Ni/C catalysts using different carbon supports for the cathode of the proton exchange membrane fuel cell (PEMFC)

Abstract

20 wt.% PtNi/C catalysts were prepared using a chemical reduction method, with Vulcan XC-72 conducting furnace black and graphene as the carbon support, respectively, and compared to commercial BASF 20 wt.% Pt/C (using Vulcan XC-72 carbon as support). The materials were characterized by X-ray diffraction, and transmission electron microscopy (TEM). The electrochemical performance of the PtNi/C catalysts was evaluated by cyclic voltammetry, and by steady-state measurements. Electrochemical measurements indicate that the PtNi nanocatalysts exhibited improved activity in the oxygen reduction reaction (ORR) on graphene compared with those on Vulcan XC-72 carbon, and graphene could potentially provide much higher durability than XC-72. This suggests that graphene is a more effective catalyst support than Vulcan XC-72 carbon.

Introduction

Proton exchange membrane fuel cells (PEMFCs) are a class of devices used for the conversion of chemical energy into electrical energy [1]. Hydrogen-fed fuel cells are attractive power sources for both stationary and electric vehicle applications due to their high conversion efficiencies and zero CO₂ emission. In particular, PEMFCs are the most promising candidates for transportation applications due to their low operating temperature (<100 °C) and rapid start-up time [2], [3], [4], [5]. However, the commercial viability of PEMFCs requires the development of better electrocatalysts to improve fuel cell performance. One of the key factors affecting the PEMFC's performance is a significant overpotential loss on the cathode side due to the slow oxygen reduction reaction (ORR) kinetics under typical conditions operation [6].

In the state-of-the-art PEMFC, platinum on carbon (usually Vulcan XC-72 conducting furnace black, Cabot Corporation, Boston, MA) is widely used as an electrocatalyst due to its excellent reaction kinetics at low temperature [7]. However, in order to further reduce cathode voltage losses, it is necessary to develop ORR electrocatalysts that are more catalytically active than platinum, which is expensive, and is in limited global supply. One approach is to synthesize platinum-based binary or ternary electrocatalysts. Several Pt-based binary systems, such as Pt–Fe [8], [9], [10], [11], [12], Pt–Ni [13], [14], [15], [16], and Pt–Co [17], [18], [19], [20], [21], with different Pt:M (M is a transition metal) atomic compositions have been investigated and have shown enhanced electrocatalytic activity towards ORR compared to Pt catalyst alone. Moreover, the presence of an alloy element reduces the costs associated with Pt.

Carbon materials usually have a high surface area to disperse metal grains, and their high conductivity transfers electrons generated from electrochemical reactions taking place on the anode. Therefore, the metal particles are often supported on carbon black (such as Vulcan XC-72) or other carbons with a high surface area. Recently, graphene, a single layer of carbon (carbon atoms in a two-dimensional (2D) honeycomb lattice) has attracted strong scientific and technological interest [22] with great application potentials in various fields, such as electronic devices [23], nanocomposites [24], batteries [25], and fuel cells [26], [27], [28]. It has been proposed that carbon materials with a higher graphite component could be more stable [29].

In this study, we have investigated Pt–Ni/C catalysts, with Vulcan XC-72 and graphene (synthesized by the method reported in [30]) as carbon supports. We found that the Pt–Ni nanocatalysts exhibited enhanced activity in the oxygen reduction reaction (ORR) on graphene compared with Vulcan XC-72.