Electrochemical and Raman spectroscopic evaluation of Pt/graphitized carbon black catalyst durability for the start/stop operating condition of polymer electrolyte fuel cells

The durability of Pt nanoparticle catalysts and two types of carbon supports, carbon black (CB) and graphitized carbon black (GCB), for 50 wt% Pt-loaded catalysts (commercial Pt/CB, and Pt/GCB, heat treated (HT) Pt/GCB, and an in-house-prepared nanocapsule Pt/GCB) was evaluated by electrochemical and Raman spectroscopic methods. The Pt-loaded carbon catalysts were tested by means of a standard potential step protocol (0.9 V ↔ 1.3 V vs. RHE, holding 30 s at each potential and taking 1 min for one cycle, 3000 potential cycles for commercial Pt/CB and 10,000 cycles for commercial Pt/GCB, Pt/GCB-HT, and nanocapsule Pt/GCB) in membrane-electrode assemblies at 65 °C with 100% RH H2 (anode) and N2 (cathode). Slower degradation of the electrochemically active surface area (ECA) and smaller mass activity losses before vs. after durability testing for Pt/GCB compared to CB revealed the higher corrosion resistance of GCB. Changes in the Raman spectra were clearly detected between the Pt/GCB catalyst before and after durability testing, while only slight differences of spectra were found for commercial Pt/CB during durability testing. The degradation degree of the graphitized carbon black support was successfully evaluated from changes in the band area ratio of the G band (ca. 1575 cm−1) to the D1 band (ca. 1325 cm−1), which were estimated from curve fitting of the spectra. It was found that the type of support material, Pt nanoparticle size, as well as its dispersion state on the support, affected the degradation properties of the catalysts. The results of the Raman spectroscopic measurements demonstrated the applicability of this technique for the evaluation of the state of the graphitized carbon black-supported Pt catalysts.

► The durability for carbon-supported Pt catalysts was investigated in voltage step cycle testing.
► The durability test revealed high corrosion resistance of Pt/graphitized carbon black catalysts.
► Changes in the Raman spectra for the Pt/graphitized carbon black catalysts were clearly detected after durability test.
► The catalysts durability was dependent upon the average size and dispersion state of the Pt particles.
► The Raman spectroscopic method demonstrated its applicability for the evaluation of the carbon-supported Pt catalysts.