Contamination of Metal Impurities during Hydrogen Evolution/Oxidation Reaction

Abstract

One of the most promising fuels in the near future will be hydrogen which should produce only by waterelectrolysis.1 Although the kinetics of the hydrogen oxidation/evolution reaction (HOR/HER) on platinumare extremely fast in acidic media, its catalytic performance tremendously drops by two order of magnitudesin alkaline media.2 To obtain kinetic parameters of electrochemical reactions, e.g. HOR/HER or oxygen reduction reaction(ORR), rotating disc electrode (RDE) experiments are the main tool in electrochemistry nowadays.Although the RDE experiments can be performed very easily, fast and cost-efficiently in the labs, reliableand reproducible evaluation of catalytic performances of materials remain still a critical challenge. Inparticular, various sources of impurities need to take into account and to be eliminated prior toelectrochemical measurements. Not till then, structure-activity relationship of electrochemical reactions cansuccessfully be uncovered. In this study, we discuss possible contamination on polycrystalline platinumduring HER/HOR in various alkaline electrolyte solutions (KOH, NaOH and LiOH). We evidently showthat the observed contamination is not caused by the used hydrogen (quality of 99.999% vs. 99.9999%) orby glass corrosion which can be avoided by frequently exchange of electrolyte solution. More importantly,we point out that trace metals stemmed from commercially available used electrolyte salts quickly depositon a pure platinum surface during the initial HOR/HER polarization measurements and dramaticallydecrease the electrochemically active Pt surface area (HUPD). In addition, we determined the losses ofHUPD over a broad temperature range in KOH, NaOH and LiOH. Interestingly, by chronoamperometricinvestigations on a platinum foil followed by surface-sensitive X-ray photoelectron spectroscopy (XPS)analysis we could detect qualitatively metal impurities originated from the electrolyte solution. We providea chronoamperometric method for further purification of electrolyte solution to reduce the contaminationand thus the HUPD losses after the HOR/HER. In this talk, we show critical approaches and solutionswhich enable reliable and reproducible HOR/HER activity measurements on platinum in alkaline media.