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The development of PEM electrolysers is closely connected to the discovery of perfluorinated ion-exchange membranes Nafion® from DuPont, and the first PEM electrolyzes were developed in the 1960s by General Electrics. In the beginning, PEM electrolysers were mainly used for oxygen generation in anaerobic environments, but over the past two decades, it has been increasingly used for hydrogen production in the industrial sector. Several companies have already put 1-10 MW-scale systems in the market and 10-100 MW systems are being announced. This chapter provides an overview of the PEM electrolysis technology, including the materials used, stack design, lifetime and performance as well as system configurations and modelling before closing with a summary of recent advances in the field as well as an outlook for future development.

An anode electrode concept of thin catalyst-coated liquid/gas diffusion layers (CCLGDLs), by integrating Ir catalysts with Ti thin tunable LGDLs with facile electroplating in proton exchange membrane electrolyzer cells (PEMECs), is proposed. The CCLGDL design with only 0.08 mg

The use of hydrogen as a zero-emission fuel and energy storage medium has the potential to play an increasing role in the decarbonization of our energy and transportation infrastructures when produced using renewable energy resources. This work proposes a load-managing photovoltaic (PV) system for driving hydrogen production that eliminates the need for power electronics without sacrificing critical features like maximum power point tracking or voltage regulation. In the proposed system, each electrolyzer stack is operated independently, rather than operating all the stacks as a single unit, allowing the system to dynamically respond to changes in available PV power. This methodology was tested in simulation by analyzing the performance of two commercial electrolyzers, each coupled with a PV array. The proposed system was able to extract over 99.5% of the available energy from the PV array, outperforming the single-unit power electronics-based approach. The compounding benefits of reducing cost and improving energy yield provide a competitive solution for PV-driven hydrogen production.

The lightest element has carried a heavy burden for half a century. Expectations for the hydrogen economy, first proposed in the 1970s, have been high. But hydrogen as a renewable, low-carbon fuel for vehicles, heating, and energy storage has remained evasive, held back by high costs, low efficiency, and a lack of infrastructure and storage technologies.

Membrane (PEM)-based electrolysis provides an ideal near-term technology to address the growing energy storage demands as intermittent renewable energy becomes more prevalent. While proton exchange membrane (PEM) systems are often viewed as preferred solutions to legacy KOH systems due to the lack of corrosive electrolyte, small footprint, dynamic operating range and ability to generate hydrogen at differential pressure, they still present capital cost challenges. In particular, the platinum group metal catalysts and valve metals for separator and flow field construction required for stability in the acidic environment become a significant cost driver at scale. Alkaline exchange membrane (AEM)-based electrolysis is therefore viewed as a potential replacement to the current PEM systems as a means of driving down the high capital cost. This cost reduction is accomplished by replacing the typical high cost catalyst and materials of cell construction with lower cost metals that would corrode in the acidic PEM environments, but are stable in the alkaline chemistries. In theory, this approach is highly promising, but testing of the current state-of the art has shown the technology gaps between the two platforms in terms of stability, durability, and operating electrical efficiency. Modeling has shown that savings realized in capital cost are typically off-set by an increase in operating expense resulting from the lower activity of the non-PGM catalysts and poor conductivity of the AEM. Additionally, thermal instability of the AEMs require stacks to be operated at lower temperatures than a typical PEM system, impacting conductivity further and slowing kinetics. Recent activities have looked at improving the mechanical properties, through the addition of mechanical reinforcements, to support pressurized operation, while operating temperature and varied concentrations of liquid electrolyte to the water feed have been explored to operationally evaluate the impact on performance and durability. The latter of these operating parameters have been shown by some groups to be effective in reducing cell operating potentials and providing overall voltage stability. However, this solution adds management and additional maintenance of handling the caustics typically used. Efforts at Proton continue to show improvements in short duration operational tests under milder conditions and potential pathways to achieve targets required to compete with incumbent technology. In this talk, some of the advancements achieved and how these have impacted the cost of the hydrogen will be discussed, as well as the longer-term targets that need to be reached in order to be a viable commercial application. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the AEM electrolysis technology cost, show the critical areas to focus on to establish equivalence with current PEM systems and what is required to go beyond. Figure 1

Commercial water electrolysis technologies, including proton exchange membrane electrolysis (PEMWE), are the only renewable hydrogen generation technologies that can achieve the U.S. Department of Energy (DOE) cost targets within the next ten years at the required scale, based on the supply chain maturity and materials performance. In particular, membrane and electrode modifications have enabled the use of advanced electrolysis membranes to achieve the efficiency targets, while nanoengineered alloy catalyst layers (CLs) have been pursued to meet the cost and efficiency targets. These advancements have been achieved by building the basic understanding to allow the successful technical development and include: (1) Mechanical and chemical understanding of membranes in liquid water below 90oC; (2) Characterization of as-deposited electrodes and MEAs after operation; (3) Water management in the anode catalyst layer, dependence on catalyst loading and porous transport layer form factor; and (4) Long-term degradation rate and stability of engineered alloy Ru-Ir alloy nanocatalysts in well-defined anode catalyst layers. Nel Hydrogen’s pathway to meet these DOE goals is through the i) use of 50-75% thinner membranes that operate at 80-90 oC, while controlling mechanical creep and gas crossover; ii) reducing the catalyst loading to 1/10th the current value on both electrodes, while controlling water distribution and the porous transport layer/catalyst layer (PTL/CL) electrochemical interface; iii) incorporation of a less stable but more active Ru containing catalyst managed on the anode side of the cell, which is achievable with lower voltage operation (accomplished via low ohmic drop in the anode catalyst layer, thinner membranes, and higher temperature operation); and iv) fabricating a membrane electrode assembly (MEA) integrating all of these characteristics. In this talk, some of the advancements achieved and how these have impacted the cost of hydrogen will be discussed, as well as the longer-term targets that need to be reached to provide the robustness required for commercial applications. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the PEM electrolysis technology cost, show the critical areas to focus on to provide the largest impact towards meeting cost target goals and what is required to go beyond. Figure 1

Anion Exchange Membrane Fuel Cells (AEMFCs) are a developing alternative to Proton Exchange Fuel Cell (PEMFC) technology. A great advantage of this technology is the possibility of replacing PGM catalysts on both anode and cathode and therefore reducing the costs. For example several PGM-free electrocatalysts have demonstrated superior fuel oxidation performance[1]. In AEM electrolysis both Hydrogen [2] and Oxygen Evolution[3] PGM-free catalysts have been demonstrated. In the present work we present unprecedented performance of a Nickel-based Hydrogen Evolution (HER) catalysts that are bifunctional for the Hydrogen Oxidation (HOR) reaction. These Nickel-based catalysts are multifunctional catalytic systems and rely on g alloying and mixed and low-coverage complementary metal oxides to fine tune surface-electrochemical interactions and reactions. While the goal of the work is to create reversible HER/HOR PGM-free catalysts, the efforts to date were focused on making the most active nickel-based bifunctional HER and HOR catalysts. Next reversible electrodes will be developed and catalyst stability under HER/HOR mode switching will be tested. (ARPA-E OPEN 2015 DE-AR0000688) A series of nickel-based catalysts were synthesized to create mixed Nickel-alloys and oxides that promote the activation of water and hydroxyl groups on the catalysts. A range of wet-chemical routes was used to produce carbon-supported NiMo, NiCu, and NiMoCu supported on a range of standard and novel Interconnected Mesoporous Carbon™ supports. The materials were characterized through physical parameters such as crystal phase, size, and surface chemistry using XRD, XPS, and Raman Spectroscopy. These materials were evaluated in membrane electrode assemblies [MEAs] using a variety of membranes and ionomers. Unprecedented PGM-free HER performance exceeding 1000 mA/cm2 @ 1.9V and HOR performance exceeding 300 mA/cm2 @ 0.65V were achieved. Reversible MEA structures for these catalysts are still being optimized. References [1] U. Martinez, et al Phys. Chem. Chem. Phys. 14 (2012) 5512-5517. [2] Bates, M. et al J Phys Chem C Nanomater Interfaces. 2015 Mar 12; 119(10): 5467–5477. [3] Bates, M. et al ACS Catal., 2016, 6 (1), pp 155–161 Figure 1