Influence of post-synthesis acid treatments on Pt/C catalyst properties prepared by polyol method for oxygen reduction reaction in proton exchange membrane fuel cells

Eight post-synthesis acid treatments were systematically compared under identical polyol-derived Pt/C preparation conditions. • Citric acid treatment at pH 2 achieved 99% Pt loading efficiency and an ECSA of 106.2 m 2 gPt −1 . • The citric acid-treated catalyst delivered an ORR mass activity of 0.279 A mgPt −1 , exceeding that of commercial Pt/C. • After 30,000 potential cycles, the citric acid-treated catalyst showed a lower ECSA loss than commercial Pt/C (25.3% vs. 42.3%). Proton exchange membrane fuel cells (PEMFCs) are promising electrochemical energy-conversion devices, but their performance is limited by the sluggish kinetics of the oxygen reduction reaction (ORR). In this study, the effects of post-synthesis acid treatment on polyol-derived Pt/C catalysts supported on Vulcan XC-72 were systematically investigated. Eight chemically distinct acids, including citric, sulfuric, phosphoric, tartaric, oxalic, nitric, acetic, and hydrochloric acids, were compared under otherwise identical preparation conditions, followed by a separate citric-acid dosage series corresponding to final pH values of 2–5. The influences of acid chemistry and post-treatment pH on Pt retention, nanoparticle size and dispersion, Pt surface oxidation state, electrochemically active surface area (ECSA), ORR activity, and durability were evaluated. Thermogravimetric analysis showed that the citric-acid-treated catalyst exhibited a residual Pt fraction of 29.68 wt%, corresponding to approximately 99% of the nominal Pt loading. XRD and TEM analyses revealed Pt crystallite and particle sizes in the range of approximately 2.2–3.8 nm, with the citric-acid-treated catalyst showing relatively small and uniformly dispersed Pt nanoparticles. At pH 2, the citric-acid-treated catalyst achieved the highest ECSA of 106.2 m 2 gPt −1 and an ORR mass activity of 0.279 A mgPt −1 at 0.9 V vs. RHE, exceeding the values measured for commercial Johnson Matthey HiSPEC™ 3000 Pt/C (91.1 m 2 gPt −1 and 0.216 A mgPt −1 , respectively). XPS further showed that the citric-acid-treated catalyst retained a relatively high fraction of metallic Pt, consistent with its favorable electrochemical accessibility and surface state. After 30,000 potential cycles, the citric-acid-treated catalyst exhibited a lower ECSA loss than the commercial reference (25.3% vs. 42.3%) and less XRD-detectable crystallite coarsening. Single-cell measurements under matched cathode Pt loading also showed higher cell voltages for the citric-acid-treated catalyst over the investigated current-density range. These results indicate that post-synthesis citric acid treatment can improve Pt retention, nanoparticle dispersion, electrochemical accessibility, ORR activity, and structural durability through acid-dependent surface and Pt–carbon interfacial effects. The present protocol was demonstrated at a laboratory scale, yielding approximately 80 mg of catalyst per batch. Download: Download high-res image (152KB) Download: Download full-size image A comparative analysis was conducted on the oxygen reduction activity of Pt/C catalysts obtained under various chelating agents and their dosages. The optimal chelating agent and its corresponding amount were identified, and an in-depth investigation was carried out to understand the factors contributing to their superior performance.