NECPEM · NOVEL PRECIOUS AND NON-PRECIOUS ELECTROCATALYSTS FOR PEMFC

NOVEL PRECIOUS AND NON-PRECIOUS ELECTROCATALYSTS FOR PEMFC

The Principal Objective of the project is to combine wet chemical synthesis, electrocatalysis and nanotechnology methodologies to prepare and evaluate the best PEMFC electrocatalyst candidates leading to high performance, durability and low cost. We split the project into four main tasks: (1) Selection and preparation of noble and non-precious metal doped carbon alloy catalysts, (2) Physical (XRD/XPS.HR-TEM) and electrochemical (CV and RDE) characterisation of the prepared catalysts and comparing the activity with commercial catalysts such as Tanaka TKK, (3) Evaluation of the fuel cell performance of prepared catalysts and mechanism of their catalytic activity, and (4) Studies of the durability of the optimised catalysts in actual fuel cell mode (in-situ testing). We have prepared FePt alloy nanoparticles supported on graphene oxide to improve the catalytic activity and durability. The amount of Fe in the catalyst was varied and based on the initial results; we stayed with a 25%Pt and 25% Fe loading on the graphene oxide support. The catalysts prepared were in the range of 5-6 nm in size as confirmed by TEM (Figure 1a) and PXRD results. All in all, we have varied the composition of Fe, Pt at 2 different ratios and tried three different supports to finalize our final catalyst composition. The preparation conditions also varied from wet chemical reduction to chemical vapour reduction procedure with 95/5 Ar/H2 gas mixtures at 300 ºC. Nevertheless, the wet chemical synthesis route provided the catalysts with better catalytic activity. The catalysts prepared by the simple wet chemical synthesis were narrowly distributed in size (Figure 1b). We confirmed the metal content of the final catalyst by TGA and XPS analysis as ~30% Pt, ~25% Fe and remaining reduced graphene oxide (RGO). XPS also confirmed the presence of functional groups in the RGO even after NaBH4 reduction. The FePt supported on RGO displayed significantly improved catalytic performance than that of the commercial PtC catalysts supplied by Tanaka, Japan. The linear sweep voltammetry (LSV) results in Figure 2a normalized to the electrochemical surface area (ECSA) of the catalysts show the superior catalytic activity of FePt supported on RGO (FePtGO) in comparison to FePt supported on carbon and PtC (5 and 3.5 times over PtC and FePtC respectively). Further, at a current density of 0.5 mA/cm2 , about 77 mV less over-potential is observed for FePtGO in comparison to that of FePtC. Similarly, the catalytic activity per gram of Pt calculated for FePtGO is comparable to that of the commercial catalyst despite its larger size (~5 nm against ~2.5 nm) which clearly indicates the superior catalytic activity of FePtGO. The ‘n’ value obtained from the Koutcheky-Levich (KL) plots suggest a direct 4 electron reduction of oxygen to water for FePtGO while two step two electron process for FePtC that involves the corrosive peroxide intermediate. We studied the durability of our catalysts by monitoring the ECSA and FePtGO retained more than 75% of the initial performance while only 50% and 25% are retained by PtC and FePtC suggesting the significantly improved cycle life of our catalyst (Figure 2B). Despite the similar particle size, RGO supported FePt displayed wonderful durability that was attributed to the shielding of Fe by Pt on one side and GO on the other side.

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