Photovoltaic-assisted H2 generatiON (PH2ON)

The development of catalyst materials and novel device designs for water electrolysis are essential to increase the share of green hydrogen production with the use of renewable energy sources. In PH2ON we have developed a platform technology for the synthesis of advanced catalyst materials of improved efficiency and catalytic versatility. The PH2ON catalysts were integrated in novel monolithic, easy to assemble and transport electrolysis devices that enabled water electrolysis at high efficiency and with solar energy as the only energy input. We showed a solar-to-hydrogen (STH) efficiency of 6.6% with a stable operation under strongly corrosive environments, as is alkaline electrolysis, for 71 h. This performance is among the highest ever recorded for this type of photo-electrolysis devices and by further engineering of our catalysts we reached an impressive STH of 10%, which is the minimum efficiency required for commercialization and scaling up at industrial levels. Further studies should focus on improving the stability and lifetime of these devices and materials as well as their scaling up in the form of modular cells, as is the case in solar cells and the PV industry. Photo-electrolysis of water and green hydrogen production is a promising way to store solar energy in the form of chemical energy and use it when the sun is not shining. Nevertheless, studies and large-scale industrial projects for the upscaling of alkaline water electrolysis have shown that water electrolyzers may “die of thirst” as their geographical placing is usually competing with local freshwater supplies. In PH2ON we addressed this challenge, and we have transferred the monolithic design from the liquid to the gas phase for the photo-electrolysis of water vapor, i.e. direct hydrogen production by ambient humidity present in air. There are 13 trillion tons of water in the gas phase in equilibrium with its liquid phase, everywhere and at any time. The gas phase photo-electrolysis system developed in PH2ON can make fuels from thin air and can provide a solution when freshwater supplies compete with needs for the local population and for irrigation purposes, as well as for the production of clean energy in arid or semi-arid regions. Finally, areas with high sunlight activity have usually limited water supplies due to a dry environment, therefore the PH2ON gas phase water vapor photoelectrolyzer poses a promising solution for localized and direct energy production, not competing with freshwater supplies.

The impact of the activities developed in PH2ON is multifold. First, we developed a platform technology for the synthesis of advanced catalytic materials for applications in photo-electrochemical energy conversion. These materials can be tailor-made with minimal engineering requirements and their application have the potential to extend beyond water photoelectrolysis, which was the main objective in PH2ON. We envision that applications include plasmonic photocatalysis and sensing, CO2 reduction to important platform or specialty chemicals, N2 fixation and NH3 synthesis, organic electrosynthesis for the production of stereoselective organic molecules and electrochemical energy storage. Second, PH2ON developed a monolithic PV-driven photoelectrochemical (PEC) device, which can electrolyze water to produce pure oxygen and hydrogen gasses with sunlight as the only energy input. In this way, we address the intermittent nature of solar energy, which can be stored in chemical energy and be used on demand. The device assembly is based on minimal engineering requirements and moreover, it is comprised mainly of earth-abundant elements, factors that increase its potential for upscaling. The solar-to-hydrogen (STH) efficiency of 6.6% and the operating stability over 71 h of continuous illumination set a benchmark performance for such systems of water photoelectrolysis. Third, and as freshwater supplies for such water electrolysis systems will soon compete with water needed for drinking and irrigation purposes for the local communities, we have transferred the applicability of the PH2ON device to the gas phase for water vapor photoelectrolysis and direct hydrogen gas production. This means that we have enabled the production of fuels from thin air. The impact of our novel water vapor photoelectrolysis system can be enormous, as we can produce fuels in arid or semi-arid regions, areas with no grid infrastructure and from diverse water sources (e.g. wastewaters, rain water). There are approx. 13 trillion tons of water in the gas phase in a dynamic equilibrium with its liquid phase, everywhere and always. Therefore, water vapor is really an inexhaustible source of water for on-site production of green hydrogen. The developments in PH2ON can spark and spearhead such a technological revolution.

Solar-driven water splitting could provide an energy dense fuel for grid-scale energy storage, but also as a feedstock for the production of carbon-neutral transportation fuels. PH2ON develops a monolithically integrated solar cell-assisted photoelectrochemical (PEC) water splitting and hydrogen production membrane. In this system, a Si-based solar cell is placed in tandem with a water splitting photocatalyst, building up the necessary photovoltage for wireless, unassisted water splitting and hydrogen production. The project combines complementary expertise in fuel cells (University of Oslo - UiO) and solar energy (Institute for Energy Technology - IFE) and evolves the planar design into a porous one, based on a porous Si solar cell. The porous PV-assisted PEC cell is used to electrolyze water vapor and it can also be installed in rural areas and areas with limited electrical grid or infrastructure. PH2ON is a system of artificial photosynthesis, which can become the basis for the development of novel materials and sustainable, carbon-neutral technologies in Norway’s future energy sector. PH2ON is supported by leading international groups in the field of electrochemistry and solar fuels. The project is coordinated by an early stage researcher and it runs for 3 years, with the ambition to establish a group of scientific excellence in the intersect of photoelectrochemical and photovoltaic technologies.