Design of a PEM electrolysis cell. Principal components of an electrolyzer cell are: The membrane electrode assembly (MEA). This consists of a proton-permeable membrane—often Nafion—each side of which is coated with an electrocatalyst. In this diagram, the MEA consists of the iridium catalyst, membrane, and platinum catalyst. Porous gas diffusion layers (GDL), often made of titanium or carbon which transfer current from the flow plates and promote the release of the product gases from the electrolysis reaction. Flow plates which separate each cell in the electrolyzer stack and which are machined with a flow path for circulation of the water. Source: Cronin et al. Click to enlarge.

PEM electrolyzers offer a number of advantages over alkaline electrolysis, including production of higher purity hydrogen, increased charge density on the electrodes leading to faster gas evolution, and the ability to operate at pressures up to 200 bar, thereby reducing the need for compression of the product gas for storage, the authors noted.

However, expense is a major drawback; accordingly a great deal of work has gone into cost reduction of these devices, with much effort going in to reducing catalyst cost by using lower cost catalysts as an alternative to the noble metal catalysts.

Ayers et al. reported that the bipolar plate assembly is the highest cost component in the stack, representing nearly 40% of the overall cost. These plates also contribute to the overall resistance of the cell and thus to the required cell voltage. This effect is more pronounced at the high charge densities at which PEM electrolyzers operate and is one of the dominating sources of cell efficiency. These plates are also essential in the mass transport of both the reacting liquid (water) and the extraction of the product gases away from the membrane and the current collectors.

Currently flow plates are typically made from graphite, titanium or stainless steel. Each of these materials has its own advantages and disadvantages. … Considering all of the above, there is no ideal material for the construction of the PEM electrolyzer flow plates.

Within the design of the flow plate, another aspect to consider is the effect of different configurations of the channels distributing the water and conducting the product gases away from the reaction sites. … An additional consideration in the manufacture of PEM electrolyzers is the weight of the system which is largely influenced by the heavily engineered flow plates, current collectors and any further engineering required to render the electrolyzer safe and stable particularly during high pressure operation.

… Herein we explore the revolutionary device fabrication potential of 3D printing to the aforementioned challenges of the design and manufacture of electrolyzer components, resulting in a new manufacturing paradigm wherein 3D printed components are, for the first time, incorporated into an electrolyzer.

—Cronin et al.

In the study, the Glasgow team used a Bits from Bytes 3DTouch 3D printer using a layer-by-layer deposition method to fabricate the plates from polypropylene. They then applied two coats of silver paint to the polypropylene flow plate, after which the flow plates were considered suitably conductive for electrocoating.

A completed coated 3D printed flow plate weighed 13.9 g—less than one-quarter of the 59.2 g of a corresponding titanium flow plate. The tam calculated that the 3D printed component would cost $0.17 per plate, compared to the $0.80 of the titanium plate.

There are issues with the resulting first-generation. As one example, performance was limited with increasing temperature; This was surprising, the authors noted, because a standard electrolyzer achieves progressively higher current densities at a given voltage as the temperature increases.

The team attributed the cause to the expansion of the polypropylene layer with rising temperature, which is greater than that of the expansion of the silver coating. This likely induces a distortion in the silver coating, increasing the distance between the particles and/or decreasing the extent of overlap, with the resulting effect of increasing the resistance of the flow plate and effectively cancelling out the expected improvement in performance at a higher temperature.

The Faradaic efficiency was 94% and the energy efficiency was 70%. They attributed the 6% Faradaic loss to parasitic electrochemical processes occurring within the flow plates, especially within the binder used in the silver paint.

Performance of the cell also declined during the 96 h of operation of the experiment. After an initial degradation, the cell was comparatively stable for about 26 hours, thereafter becoming even more stable. While the reason for the distinct rates of degradation are not known, they are likely to be associated with electrochemical degradation of the binder components of the silver paint and oxidation of any exposed silver crystallites and concomitant degradation of both conductivity and membrane performance, the authors suggested.

We have demonstrated that a viable, practical electrochemical device can be fabricated using a 3D printer and appropriate surface coatings. The potential for rapid prototyping should allow for exploitation of the optimal flow plate geometries for a given device. The reduction in cost and weight should prompt further exploration of the potential of renewable hydrogen production and use in applications demanding such properties. Further work in this area will include extension of the application of 3D printing to other electrochemical devices, e.g. fuel cells and the further investigation of different materials and coating methodologies.

—Cronin et al.

Resources

• Lee Cronin, Greig Chisholm, Philip Kitson, Niall Kirkaldy and Leanne Bloor (2014) “3D Printed Flow Plates for the Electrolysis of Water: an Economic and Adaptable Approach to Device Manufacture,” Energy Environ. Sci. doi: 10.1039/C4EE01426J