Demand for hydrogen could climb to 500 million tons by 2050. Unfortunately, this consumption comes at a high climate cost as more than 95% of hydrogen is produced for refining and chemical processing from natural gas, with 6 tons of CO2 being released for each ton of hydrogen produced. To provide green hydrogen for power, fuel, refining and chemical production, the world is increasingly turning to water electrolysis as a source of hydrogen. This process does not produce any CO2 and when powered by stranded renewable energy it is totally carbon free. 

One of the critical functions inside the electrolyzer is provided by the cathode GDL. While the GDL allows  hydrogen produced in the cell to move out of  the cell, more importantly it acts to provide compliance in response to changes in temperature, and also to enable electrochemical efficiency. PEM Electrolyzer cathode GDLs  are generally based on fuel cell materials such as carbon papers, with and without microporous layers.

AvCarb has invested millions of dollars in the improvement of GDL technology, and the end result is a wide portfolio of products used in high volume by fuel cell manufacturers worldwide. Today, AvCarb® GDL products can be found in tens of thousands of hydrogen fuel cell stacks around the world, in both stationary and transportation applications. We are now applying this expertise to the Cathode GDL in PEM electrolyzers.

PEM Electrolysis is a close sibling of PEMFC, utilizing many of the same electrochemical cell components such as PGM catalysts, BiPolar Plates, PFSA membranes and carbon diffusion or transport layers on the cathode side. As with a fuel cell, many individual cells are combined in a stack to yield a functional electrolyzer.

As shown in the diagram to the right, water enters the PEM cell on the anode side which utilizes a titanium transport layer, and is split into hydrogen and oxygen through an electrochemical process on the membrane, with hydrogen and water exiting on the cathode side, and oxygen and water exiting on the anode side. While PEM electrolysis can have high capital costs due to the use of PGM and PFSA membranes, costs are continuing  to fall as volumes increase due to the advantages that PEM Electrolysis provides. Among these are its quick start and dynamic range capabilities, electrical efficiency, gas purity, less complex balance of plant and smaller footprint.

ALK Electrolysis is a chemical process whereby water is electrolyzed utilizing an alkaline electrolyte made with KOH. It is a time-proven process, first developed over a century ago, and while its capital costs are lower, operational expenses are higher due to corrosion caused by KOH. While it is well suited for steady state processes, it does not have the quick start and dynamic range capabilities of PEM. Gas purity is also lower, requiring additional processing in the balance of plant to bring purity to acceptable levels. This, when combined with the additional equipment needed to maintain and pump KOH levels, results in a larger and more complex balance of plant with higher costs. The electrical efficiency of ALK is also a bit lower than PEM.

Since it does not use PGM catalysts or PFSA membranes, AEM Electrolysis holds the promise of providing capabilities similar to that of PEM, but at lower capital costs. Like PEM, AEM also utilizes a carbon PTL on the cathode side, but like ALK, it also utilizes KOH or K2CO3 to produce the hydroxide ions needed to drive the process. As such, this can cause maintenance issues and increase the complexity and cost of the balance of plant. AEM is in its infancy and is several years away from the market.