Electrolyzer technology development

The development of electrolyzer technology for the production of hydrogen as a vehicle fuel is aimed at several issues ... 

The cost estimates presented here are based on existing technology. This implies that capital-related cost may come down in the future as technology develops. We note, however, that many of the main capital items, from SMR plants to hydrogen compressors, are essentially mature technology, and the scope for further cost reduction is relatively small. The case may be different for forecourt reformers and forecourt electrolyzers, but, as will be elaborated below, the effect thereof is relatively limited. 

Key technology developments Ballard PEM fuel cells and Stuart Energy electrolyzers. 

Currently there are two primary distributed electrolyzer technologies in development and use (1) Alkaline electrolyte electrolyzers and (2) Proton-exchange membrane electrolyzers. 

Much like metal recovery from dilute streams, the use of three-dimensional electrodes will enhance the oxidation rates of low-concentration organics by increasing the surface area available for reaction. Moreover, porous electrodes which could be incorporated into cells using solid electrolytes can draw upon technologies developed for other electrochemical systems such as PEM-based water electrolyzers and fuel cells. 

This is an area of much practical importance for research and development in electrolyzer technology more work is currently required for elucidation of the behavior of high-area porous and composite electrode materials with regard especially to the values of Tafel slope and conditions under which low b values can be achieved for H2, O2, and CI2 evolution reactions, thus minimizing activation overpotential energy losses in high current-density operations. 

The technological development of electrolyzers started with a mono polar cell consisting of a cathode part and an anode part separated by a diaphragm, hi multi-cell systems, bipolar plates are used carrying the cathode material for one cell and on its backside the anode material for the neighbor cell. The functions of the bipolar plate are the continuous supply of the membrane electrode with H2 on one side and with O2 or air on the other side and the regulation of the water balance by providing moisture for the membrane on the H2 side and remove the product water on the O2 side. 

Ni M, Leung M K H and Leung D Y C (2008), Technological development of hydrogen production by solid oxide electrolyzer cell (SOEC) , Int J Hydrogen Energy,33,2331-2354. 

Most current technology development is focused on the use of platinum (or platinum and ruthenium) supported on carbon particles, in order to reduce the amount of platinum required on the anode down to 0.05-0.45 mg cm", as described in [10]. These types of anodes are prone to degradation during fuel starvation due to the reaction in Equation 17.6, the oxidation of carbon, which is catalyzed by the presence of platinum [11]. This reaction proceeds at an appreciable rate at the electrode potentials required to electrolyze water in the presence of platinum (greater than approximately 1.4 V [24). This is shown schematically in Figure 17.4. The catalyst support is converted to CO2, and Pt and/or Ru particles may be lost from the electrode, resulting in loss of performance. 

In conclusion, it is now over 120 years since the alkaline electrolyzer emerged, and over 50 years since PEM and SO electrolyzers were developed. While exact data are hard to come by, almost all (99%) of the crurerrt market for electrolyzers is dominated by alkaline technology. However, in recent years, PEM electrolyzers have noticeably gained ground. As was slated in section 2.1, water electrolysis accormts for a very marginal proportion (less than 1%) of worldwide hydrogen production. 

The experimental work done to date in the reaction kinetics of SO2 depolarized electrolyzers, electrocatalyst evaluation, and tests on small experimental cells has led to projections of cell voltage for a mature technology. Table III presents these projections, as a function of electrolyte concentration and operating temperature. These projections will be refined, as the development work progresses, to expand the matrix of variables, increase the confidence level in the figures, and define an optimum set of operating parameters. 

PEM technology was originally developed as part of the Gemini space program.16 In a PEM electrolyzer, the electrolyte is contained in a thin, solid ion-conducting membrane rather than the aqueous solution in the alkaline electrolyzers. This allows the H+ ion (proton) or hydrated water molecule (HsO+) to transfer from the anode side of the membrane to the cathode side, and separates the hydrogen and oxygen... 

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