As materials science is becoming components development and systems technology, hydrogen economy is approaching your porch. Welcome!

Hydrogen mobility can now be purchased from the shelf. Fuel cell electric vehicles from various well-known car manufacturers are now available. The number of hydrogen filling stations in Europe is increasing at a rate that long-distance tours become less and less adventurous. The efforts of fuel cell researchers have paid off. Suppliers of components and systems for hydrogen infrastructure are anticipating business. Meanwhile, basic science in electrochemistry and materials research is continuing, with surprises such as the discovery of a proton polaron which are adding to the progress in fundamental understanding of energy materials in operation. Has the long awaited hydrogen economy finally arrived?

Direct photoelectrochemical water splitting offers several advantages over PV-powered electrolysis and may become the technology of choice in the future. However, significant R&D efforts and breakthroughs are needed to accomplish this goal.

The sustainable production of hydrogen would be an important first step for both powering fuel cells and for enabling large-scale and technologically mature gas phase processes to reduce CO2 and nitrogen to get desired products. Specifically, the central challenge is to produce hydrogen from water using sunlight. Photovoltaics and wind-powered electrolysis are likely to be the technology of choice to produce renewable hydrogen for the next few decades. However, the integration of light absorption and catalysis in ‘direct’ photoelectrolysis routes offers several advantages, such as lower current densities and better heat management, and may become technologically relevant in the second half of this century. This article discusses the research and development efforts and needed breakthroughs to achieve this goal. New chemically stable semiconductors with a band gap between 1.5 and 2.0 eV and long carrier lifetimes are urgently needed to make efficient tandem devices. Scale-up of these research level devices beyond a few cm2 introduces mass transport limitations that require creative electrochemical engineering solutions. Last but not least, standardized methods for measuring efficiencies and stabilities need to be implemented and should lead to official benchmarking and certification laboratories to guide commercial scale up efforts.

Sustainable, carbon-free methods of large-scale hydrogen production are urgently needed to support industrial processes while decreasing carbon dioxide emissions. The realities of product development timelines dictate that existing commercial technologies such as low-temperature electrolysis will have to serve the majority of this need for at least the next 20 years. At the same time, even a cursory understanding of device design principles and real-world constraints can help to inform basic research. Accelerating the impact from fundamental material discoveries in related technologies therefore requires improved collaboration between academic, government, and industry sectors.

Renewable hydrogen is a key component to global decarbonization and reduction in carbon dioxide emissions. A common misconception is that the need for greener sources of hydrogen is dependent on whether fuel cell vehicles significantly penetrate the automotive market. However, hydrogen is a critical feedstock for many industrial processes, with an annual demand of 65 million metric tons globally. The large majority of this hydrogen is made via steam methane reforming, which represents the major carbon dioxide contribution for industrial processes such as ammonia production. Sustainable manufacturing of hydrocarbons also requires a sustainable source of hydrogen. Deep decarbonization and meeting 80% reduction targets for carbon dioxide emissions thus requires carbon-free sources of hydrogen. Based on the technology readiness levels, the reality is that existing commercial technologies will dominate the market for the next 20 years and beyond. To accelerate the impact of fundamental work in long-term technologies, improved collaboration between researchers across academic, government, and industry sectors is essential, to inform basic research as well as to leverage technology breakthroughs in the near term.