On the Suitability of Proton Pump Experiments to Evaluate New Hydrogen Evolution Electrodes for PEM Electrolysis Cells

Abstract

The increased interest in green hydrogen has fostered an increased interest in electrolysis technology and in particular PEM-electrolysis as it allows currently best to absorb intermittent occurring renewable excess current. The challenge is the high expenditure of scarce PGM materials in PEM electrolysis cells. While this is most relevant for the iridium used as anodic oxygen evolution catalyst still also a reduction of the platinum expenditure at the cathode would at least serve to the Capex for PEMEL facilities. The group of Prof. U. Apfel at Ruhr University Bochum and Fraunhofer UMSICHT in Oberhausen is investigating pentlandite based hydrogen evolution catalyst for this purpose1 . Within the Fraunhofer internal project CINES, Fraunhofer ICT had the task to develop hydrogen evolution electrode from this catalyst. Now, as the hydrogen evolution and hydrogen oxidation in an acidic environment are both very fast reactions2 the difficulty is to monitor this reaction in a full electrolysis cell versus a oxygen evolution electrode with much more sluggish reaction. The idea was therefore to employ proton pumping as experiment wherein the electrode which is tested is used as cathode and a standard Pt/C electrode at a reasonable platinum loading as anode. In that way the performance of the new hydrogen evolution electrode should be much easier to evaluate.In a first step a commercial fuel cell CCM bought at Quintech, Germany was compared to a homemade CCM with platin layers on both sides both operated as proton pump. The results show that the performance differ in detail. So, the initial voltage loss due to charge transfer resistance is smaller for the commercial CCM likely due to the use of a more performant catalyst. The homemade CCM perform better however in the ohmic region. For both type of CCM the voltage at 800 mA cm-2 did not exceed -0.12 V (cf. Fig 1).In comparison first test with the Pentlandite based HER catalyst showed a strong over potential increase at low current densities and a hysteresis between the forward and the backward scan. The strength of the hysteresis did depend on the type of pentlandite (cf. Fig 2). After discussion with Prof Apfel’s group the effect of hot pressing was evaluated. It was found that hot pressing helped to reduce the over potential and in particular strongly reduce the hysteresis of the polarization curves (cf. Fig 3).If the results from the proton pumping are now compared to results obtained in a PEM electrolyser cell (cf. Fig. 4) it becomes obvious that many features observed in the proton pump experiments can be found here to. This is in particular true for the strong potential increase at low current densities.In total it can be said that proton pump experiments can be used to evaluate hydrogen evolution catalyst for PEM electrolysis at least in an initial stage. More experiments and details will be discussed in the presentation. B. Konkena, K. junge Puring, I. Sinev, S. Piontek, O. Khavryuchenko, J. P. Dürholt, R. Schmid, H. Tüysüz, M. Muhler, W. Schuhmann and U.-P. Apfel, Nat Commun, 7(1), 12269 (2016).J. Durst, C. Simon, A. Siebel, P. J. Rheinländer, T. Schuler, M. Hanzlik, J. Herranz, F. Hasché and H. A. Gasteiger, ECS Transactions, 64(3), 1069–1080 (2014). Figure 1