PDF Publication Title:
Text from PDF Page: 060
60 GREEN HYDROGEN COST REDUCTION PEM electrolysers For PEM stacks, the focus areas are bipolar plates and PTLs, given their large cost contribution and large potential for reduction. Based on these two criteria (cost share and potential), the catalyst- coated membrane is the next priority. Re-designing the stacks can achieve large cost reductions, since it enables the reaching of higher power densities, up from the current (conservative) 2A/cm2 to 6A/cm2 or more in the next few decades. Next, electrodes should be scaled up from the current 1 500-2 000 cm2, up to 5 000 cm2 and eventually 10 000 cm2. The larger area should go in tandem with more mechanically robust membranes that can use the same thickness. Such a strategy would allow an increase in the size of the PEM stacks, from the current 1MW/unit to next generation stacks of 5 MW or even 10 MW per stack. These need to run at much lower levels of cell voltage to allow for an increase in efficiency and the simplification of waste heat management. Reducing membrane thickness: This enables an increase in efficiency, which in turn enables a reduction in electricity consumption. Thick membranes (Nafion N117 with approximately 180 μm thickness, for example) are still state-of- the-art and are responsible for efficiency losses of about 25% (at 2 A/cm2). There are much thinner membranes that are commercially available, with thicknesses as low as 20 μm, yet these are not designed for electrolysis requirements. This thickness reduction would allow a reduction in efficiency losses to about 6% (at 2A/cm2). Further reduction of membrane thickness, down to 5.0μm or lower (membraneless electrolysis), is not encouraged, since a decrease of no more than 0.5 kWh/Kg H2 can be extrapolated. In this case, R&D is therefore not justified. Looking at the experience in PEM fuel cells (reverse process of electrolysis), commercial stacks are already equipped with membranes that are 810 μm thick, as gas permeation is not a concern, since they operate a much lower pressures (36 bar) on the air side. The two challenges that arise with thinner membranes are: their lower durability, given their potentially lower mechanical strength and being more prone to defects and pinhole failures; and the manufacturing of such membranes. During manufacturing, the process of enlarging the catalystcoated membranes and porous transport layers into large electrodes is challenging and therefore of high R&D risk. The thin membrane and electrodes need to be mechanically stabilised over the full area to avoid undesired mechanical stresses that can tear these films and delaminate thin electrodes. This is especially critical at differential pressure operations, where one side is subjected to much higher pressures coming from the other electrode. Re-designing PTLs will be crucial – i.e. with finer structures at the catalyst interface that can better support a thinner membrane and prevent creep failure, thereby enabling lower membrane thickness. Removing expensive coatings and redesigning the PTLs and bipolar plates: On the anode side, commercial stacks demand the use of platinum- coated titanium porous sintered PTLs, which is not possible with non-PGMs at this stage. Platinum loadings on the anodic PTL vary from 1-5 milligrammes per square centimetre (mg/cm2) or 1 2.5 g/kW. Platinum has a dual purpose: to protect the titanium against passivation17 and provide an optimal interface resistance. This is needed because titanium is prone to severe quick and detrimental passivation. Studies have shown that interface resistance at the PTL is responsible for an electricity consumption as high as 1.35 kWh/Kg H2 (4% of hydrogen LHV) (Liu et al., 2018; Kang et al., 2020). The bipolar plates made of titanium also possess protective layers of platinum on the anode side, and gold on the cathode. Alternatives are needed for titanium plates, based on such materials as niobium, tantalum and eventually stainless steel approaches, but using protective coatings that are stable and also free from platinum or gold. Re-designing catalyst-coated membranes: For catalyst coated membranes (electrodes), the strategy can be divided into different timescale scenarios. An initial approach could be to tackle 17 ‘Passivation’ refers to a material becoming less affected or corroded by the environment.PDF Image | GREEN HYDROGEN SCALING UP ELECTROLYSERS
PDF Search Title:
GREEN HYDROGEN SCALING UP ELECTROLYSERSOriginal File Name Searched:
IRENA_Green_hydrogen_cost_2020.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
CONTACT TEL: 608-238-6001 Email: greg@salgenx.com (Standard Web Page)