Decoupled Electrolysis for the Production of Zero-Carbon Hydrogen

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In order to produce green hydrogen at scale from the electrolysis of water, new electrolysers that are more compatible with intermittent renewably-generated power must be developed. This is because existing electrolysers suffer from two key drawbacks which hampers their adoption for green hydrogen production driven by renewable power sources. Firstly, existing electrolysers do not handle intermittent power inputs effectively. Renewable power sources are by definition intermittent (sometimes the sun shines, and sometimes it doesn't, and when it is shining its intensity on the ground is constantly varying). If connected directly to a solar panel for example, a conventional electrolyser would be operating in constant stop-start mode. This accelerates the degradation of expensive components in the electrolyser and also leads to the production of dangerous mixtures of the hydrogen and oxygen products of electrolysis. As such, conventional electrolysers require significant power management apparatus in order to work safely using renewable power inputs. Without such power management systems, conventional electrolysers would produce dangerous mixtures of hydrogen and oxygen when coupled directly to renewable power sources, which hitherto has been a major barrier to the realisation of a hydrogen production economy driven by renewable power. The second major drawback of conventional systems is their high operational and maintenance costs. State-of-the-art electrolysers contain expensive membranes to try and keep the hydrogen and oxygen products separate, but these degrade rapidly during operation and must be replaced regularly. This adds considerable cost and complexity to long-term electrolyser operation.In this proposal, we will build on the concept of "decoupled electrolysis" to develop a system that can use solar power directly for the electrolysis of water. A decoupled electrolysis approach has the potential to solve both of the key issues preventing greater uptake of electrolysis for green hydrogen production. Indeed, in our preliminary results, we have shown that decoupled electrolysis allows the effective and safe use of power inputs characteristic of renewable sources under conditions where a conventional electrolyser produced a hazardous mixture of hydrogen and oxygen. In contrast, the gases produced by the decoupled system were well within regulatory limits in terms of mixed gas content. We were also able to show that membrane degradation was significantly reduced in a decoupled system relative to a conventional system, suggesting that decoupled electrolysers should require less downtime and incur lower maintenance costs than conventional "coupled" electrolysers. Both of these features could be expected to make electrolysis of water to produce green hydrogen significantly more practical and cost-effective. By leveraging the ability of decoupled electrolysis to allow hydrogen and oxygen generation to take place in separate places, at separate times and at rates that are not connected to each other, we aim in this project to demonstrate the production of pure hydrogen at pressure driven by sunlight. This will open the door to future scale-up of these systems for safe and efficient production of zero-carbon hydrogen driven by renewables.