The Effect of Heteroatom-Doped Graphene Supports on the PtNPs Electrocatalytic Activity for ORR

Abstract

There has been a global shift in energy production emphasizing the reduction of fossil fuels by the augmentation of more renewable energy. Proton-exchange membrane fuel cells (PEMFC) and anion-exchange membrane fuel cells (AEMFC) can mitigate a need for fossil fuels and provide an alternative route of hydrogen-based energy production. Fuel cells utilize a catalyst at both the cathode and anode to increase the overall kinetics of the redox reactions and enhance the cell performance.1 Current fuel cell technology employs a platinum based catalyst due to its efficiency and robust performance in both alkaline and acidic environments.1,2 The drawbacks associated with Pt-based catalysts are centered around its economic viability and its affinity towards surface poisoning.1 A catalyst using platinum nanoparticles (PtNPs) loaded onto a graphene support can address some of the aforementioned drawbacks.1 To maximize the electrocatalytic activity of the PtNPs – all aspects of the PtNPs catalyst must be optimized, which includes the optimization of the support material. The effect that the different commercially available heteroatom-doped graphene had on the activity of the PtNPs was investigated during this study. The PtNPs were synthesized using the citrate method, which produces ≤ 5 nm size particles. Our study confirmed that the choice of doped graphene support has an effect on the overall activity of PtNPs. The results were confirmed via a comparison with PtNPs supported on Vulcan XC-72R carbon. All Pt catalysts supported on the doped graphene showed an improvement in the oxygen reduction reaction (ORR) half-wave potentials (E 1/2) over PtNPs on Vulcan XC-72R carbon (Fig. 1A); with the nitrogen-doped graphene exhibiting the greatest improvements in the half-wave potential with the E 1/2 value of 0.85 V vs. RHE as compared to the 0.77 V of the Pt/C. A comparison of the Tafel slopes (Fig. 1B) confirmed that the transfer of the first electron was the rate-determining step for all of the Pt catalysts supported on doped graphene as all Tafel slopes were around -120 mV per decade. This has been confirmed in literature with Pt on various carbon supports.2 Figure 1. A) Comparison of RDE polarization curves for oxygen reduction on Pt/NGr (pink), Pt/SGr (green) and Pt/N-PGr (blue) with Pt/C (black) at 1900 rpm in a O2-saturated 0.1 M HClO4 solution (v= 10 mV s−1). B) Mass transfer corrected Tafel plots derived from A