Novel Components for PEM Electrolysis: Status and Challenges
Authors: Gago Aldo Saul , Lettenmeier Philipp , Wang Li , Kolb Svenja , Burggraf Fabian , Friedrich K. Andreas 
Published: February 2020

Current energy policy requires the replacement of energy sources based on fossil energy carriers by renewable energy ones. Due to the substantial discrepancy between the temporal availability of renewable energy (e.g. differences between day/night or winter/summer especially for solar energy input) and the actual needs, the opportunity of temporarily store excess energy is of great interest. In such scenario, hydrogen can act as a carbon neutral energy vector when being produced by water electrolysis using renewable energy such as wind or solar power [1]. Commercially, hydrogen can be electrochemically produced by alkaline and proton exchange membrane (PEM) electrolysis [2], but the investment cost of the latter is currently almost three times higher than that of the former [3]. However, PEM electrolysers boast the advantages of operating at much higher current densities than the alkaline systems [4]. They also offer a significant opportunity to reduce costs owing to their compact design, but the lifetime of PEM electrolysers at high performance is still unknown. There is an urgent need to reduce the cost of PEM electrolyzers for large-scale storage of surplus electricity. Recently, an EU-funded study reported that 51% of the cost of the stack is attributed to the BPPs, followed by 10% corresponding to the membrane electrode assembly (MEA) manufacture, and only 8% to the precious metal group (PMG) catalysts [5]. Moreover, the stack itself constitutes 60% of the cost of the entire PEM electrolyser system. One approach for reducing cost is by operating the PEM electrolyzer at high current densities (up to 5 A cm-2) without apparent lost in cell performance (2000 h), although MEA degrades. Another way is by reducing material and manufacture cost of the stack. We have developed dense coatings of Ti on stainless steel substrates by vacuum plasma spraying (VPS). Surface modification with a 50-fold lower thickness coating, can prevent the passivation of the Ti coating. In addition, a VPS backing layer deposited on the current collector improves the contact with the catalyst layers, increasing significantly the efficiency of the device at high current densities. The cost of the PMG anode catalyst (Ir) will become a serious issue for the large scale PEM Electrolysers. Word reserves of iridium are no sufficient for overcoming this challenge. We have synthetized a cost-effective and environmentally friendly synthesis on IrOx-Ir catalyst [6]. It is up to 5 times more active anode than commercial Ir-black. Better utilization of Ir nanoparticles can be achieved by supporting then on Ti4O7. The catalytic activity of Ir has been slightly increased with V and stability of Ru has been improved with Ir. Thus, we have addressed some of the most critical issues in system, bipolar plates, current collectors and catalysts of PEM electrolyzers.
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