Projected Fuel Cell Stack Costs Using Non-PGM Cathode Electrocatalysts

Abstract

Platinum is typically used at the cathode of the cathode of proton exchange membrane fuel cells (PEMFCs) to overcome the kinetic limitations of the oxygen reduction reaction (ORR) to water. Pt is a noble metal that is mined mainly in South Africa and Russia. At present costs of $965 per troy ounce ($31 per gram), the cost of Pt in the cathode is approximately 40% of the total cost of each PEMFC membrane electrode assembly (1,2). Supply chain concerns have been raised that there is insufficient Pt in the world to support the conversion of all automobiles to hydrogen, or that increasing the demand of Pt through mass commercialization of fuel cells would drive up its demand and then cost (1,3). Researchers have therefore looked for catalysts that do not contain Pt or other precious metals (3). Oxygen reduction without Pt is possible, and all living creatures and plants use cytochrome enzymes with reactive iron or copper sites as part of a catalytic cycle to reduce O2 to reactive oxygen. Significant improvements have been gained in the performance of fuel cells with non-PGM cathodes by improving the density of sites and improving the catalyst durability (4).We estimate the cost impact of eliminating Pt from the cathode of a heavy-duty fuel cell stack. The calculations are based on the comparison of Plug fuel cells with Pt cathodes, compared to literature polarization curves for cells and stacks containing PGM-free cathodes (note that the anodes still contain Pt). We carry out a sensitivity analysis using different costs to the non-PGM catalysts. Our primary finding is that eliminating Pt from the cathode does little to reduce stack costs because the performance of the fuel cells with non-PGM cathodes is low, and larger stacks are needed to meet performance requirements. We will also discuss how using a non-PGM cathode affects projected recycling costs.