Initial Approaches for Developing Low-Cost Materials for PEM Water Electrolyzer Porous Transport Layers

Abstract

Capital cost is a major barrier to the widespread commercialization of water electrolysis technology. Metal-based stack components, particularly the porous transport layers (PTLs) and bipolar plates (BPPs), are estimated to represent 30-70% of electrolyzer stack cost [1]. Current commercial approaches utilize titanium, which forms a passive oxide film that provides corrosion resistance in the electrolyzer anode environment. During operation, however, the electrically resistive surface oxide film grows, which leads to significant increases in cell and stack series resistance losses. Successful mitigation strategies so far have relied on a platinum-group metal (PGM) coating. With titanium alloy base materials and PGM coatings being relatively expensive, there is significant potential to reduce electrolyzer stack cost by using alternative materials.In the more advanced trajectory of fuel cell research and development, there has been considerable exploration and validation of a variety of base materials and surface modifications [2]. The primary materials have been metals or carbon-based (e.g. graphite bipolar plates or carbon paper diffusion media). Although potentially suitable in the electrolyzer cathode environment, carbon is not stable under the highly oxidizing and acidic environment of an electrolyzer anode. Therefore, metal alloys that form passive oxides are necessary, but such passive oxides generally have high electrical resistance. This defines the primary design challenge for engineering new PTL materials.In efforts toward selecting, screening, and developing promising, low-cost PTL materials, we have explored and developed ex-situ characterization techniques to be used in concert with in-situ PTL performance validation. Ex-situ measurements include interfacial contact resistance, electrochemical corrosion current, permeability, and insulating oxide formation. One facet of ex-situ corrosion testing methodology involves individually varying stressors such as temperature, pH, and potential to quantify the influence of each. Another facet employs time-lapse microscopy to observe and interpret distinct corrosion modes. These approaches will be discussed and example results for baseline and low-cost PTL materials and surface modifications will be presented.