New hydrogen production breakthroughs for cheap clean energy Hydrogen is a clean energy carrier as long as electrolysis is powered by renewable electricity. However, integration of water electrolysis to intermittent renewable energy sources (RESs) imposes a number of challenges that have now been successfully addressed by EU-funded researchers. Energy © Regine Reissner The EU is committed to reducing dependence on fossil fuels to decrease greenhouse gas emissions while increasing energy security. Use of RESs will require improved technology and more efficient management of variable loads. Hydrogen production from water electrolysis is a promising way to compensate for fluctuations in RESs. Alkaline water electrolysis is well established, but electrolysers must be improved. Within RESELYSER (Hydrogen from RES: Pressurised alkaline electrolyser with high efficiency and wide operating range), researchers developed high-pressure, highly efficient and low-cost alkaline water electrolysers that can be integrated with RESs using advanced membrane concepts, efficient electrodes and new cell designs. The newly developed 300 cm2 alkaline electrolyser cell works at high operating pressures and can be integrated with RESs. Optimised for intermittent operation, it demonstrates stable and high efficiency even in on/off cycles during long-term operation with RESs. This should facilitate market penetration in wide-ranging applications. Researchers successfully demonstrated a novel separator membrane, the 'e-bypass' three-layer composite membrane with internal electrolyte circulation. Two adjacent separator layers are interposed with a bypass channel. This channel accommodates a fresh stream of electrolyte solution to improve lower load operation at higher pressures for a wider range of operating temperatures. Innovative cell designs improved mass transfer and reduced gas impurities at high pressures and low power operation. The e-bypass separator makes electrolysis possible at very low loads (current densities far below 0.2 A/cm2) and high to very high pressures (far above 30 bar). Classic electrolysis yields severely contaminated gasses under these conditions. However, the third compartment and the electrolyte flow from inside the e-bypass resolve this issue. The gas impurity at 30 bar operation was found to be approximately the same as for 10 bar in a conventional stack. Advanced electrolyser electrodes were produced by coating plain nickel electrodes with an active layer, without the use of expensive noble metals. In addition to lower cost, they enable a 50 % reduction in electrode losses compared to conventional electrodes. RESELYSER developments led to facilitating the connection of electrolysers to intermittent power sources. Electrolysers can stabilise the contribution of variable renewables, providing energy storage services while also generating transport fuel in support of the future hydrogen economy. Keywords Hydrogen production, clean energy, electrolysis, renewable energy sources, RESELYSER
