Manufacturing of Low Catalyst Loading PEM Electrolyzer Meas Using Reactive Spray Deposition Technology

Proton exchange membrane (PEM) water electrolysis is a low temperature, low carbon footprint technology for the production of high purity hydrogen.  PEM electrolyzers can operate at higher current densities and higher pressures with lower gas crossover and a more compact physical footprint than other water electrolysis processes such as alkaline electrolyzers and solid oxide electrolyzers. However, PEM electrolyzers require expensive, noble metal catalysts and a considerable effort is currently underway to minimize catalyst loading to reduce cost, which crucial for the penetration of PEM electrolysis technology into the market. [1]

Ir or IrO₂ is generally recognized as the state-of-the-art electrocatalyst for oxygen evolution reaction (OER) at the anode, while Pt remains the best candidate for the hydrogen evolution reaction (HER) at the cathode [1,2]. The catalyst loading on the cathode is typically at least 0.5-1.0 mg/cm², whereas the anode catalyst loading is around 2 mg/cm²[1].

Reactive spray deposition technology (RSDT) has proven to be a cost-effective method for producing high performance PEM electrolyzer membrane electrode assemblies (MEAs) [3,4]. RSDT is a flame-based method that combines catalyst synthesis and processing in a single step and has the flexibility in optimizing the catalyst composition, making gradient and other complex structures possible. This has allowed our team to reduce the cathode Pt loading below 0.2 mg/cm²with enhanced performance compared to the standard baseline(Figure 1 a).

Xu and Scott studied the effect of ionomer content in the catalyst layer on PEM electrolysis using decal transfer method and the optimum ionomer content for cathode was found to be 20% [5]. However, at such low Pt loading, we found that the catalyst layer structure and ionomer content becomes more important than catalyst loading, meaning that each catalyst formulation needs to be carefully controlled.  Since RSDT is a dry deposition process, the catalyst layer formation mechanism can be different from catalyst-ink spraying and drying process. Therefore, in this talk we will focus on the role of the catalyst layer pore structure and I/C ratio in dictating the performance of RSDT-derived PEM electrolyzer MEAs.

Studies on ITO as fuel cell [6-7] or electrolysis catalyst [8] support have shown good stability above 1.4V and high performance.  Recent work has also shown the feasibility of using RSDT to directly deposit both ITO-supported and unsupported Ir/IrO₂ with ~0.1 mg/cm² Ir loading and initial MEA performance close to the baseline. Figure 1 c shows the TEM micrograph of Ir/IrO₂particles supported on ITO. The processing variables being explored to achieve stable and high performance with low Ir loading will be discussed. 

Figure 1. a) PEM electrolyzer performance using RSDT fabricated Pt/C as cathode and Ir/IrO₂; b) electrolyzer performance using RSDT fabricated Ir/IrO₂ supported on ITO as anode and Pt/C as cathode; c) TEM micrograph of Ir/IrO₂supported on ITO nanoparticles 

References:

[1] Carmo, M, Fritz, D.L., Mergel, J., and Stolten, D., Int. J. Hydrogen Energy, 2013, 38, 4901-4934.

[2] Park, S., Shao, Y., Liu, J., and Wang, Y., Energy Environ. Sci., 2012, 5, 9331.

[3] Roller, J., Arellano-Jimenez, M.J., Jain, R., Yu, H., Carter, C.B., and Maric, R., J. Electrochem. Soc, 2013, 160, F716-F730.

[4] Roller, J., Renner, J., Yu, H., Capuano, C., Kwak, T, Yang, W., Carter, C.B., Ayers, K, Mustain, W.E., and Maric, R., J. Power Sources, 2014, 271, 366-376.

[5] Xu, W., and Scott, K., Int. J. Hydrogen Energy, 2010, 35, 12029-12037.

[6] Liu, Y., and Mustain, W.E., J. Am. Chem. Soc, 135 (2014) 530-533.

[7] Liu, Y., and Mustain, W.E., Electrochim. Acta, 2014, 115, 116-125.

[8] Puthiyapura, V.K., Pasupathi, S., Su, H., Liu, X., Pollet, B., and Scottt, K., Int. J. Hydrogen Energy, 2014, 39, 1905-1913.