Hydrogen as a carrier of renewable energies toward carbon neutrality: State-of-the-art and challenging issues

Energy storage and conversion via a hydrogen chain is a recognized vision of future energy systems based on renewables and, therefore, a key to bridging the technological gap toward a net-zero CO2 emission society. This paper reviews the hydrogen technological chain in the framework of renewables, including water electrolysis, hydrogen storage, and fuel cell technologies. Water electrolysis is an energy conversion technology that can be scalable in megawatts and operational in a dynamic mode to match the intermittent generation of renewable power. Material concerns include a robust diaphragm for alkaline cells, catalysts and construction materials for proton exchange membrane (PEM) cells, and validation of the long-term durability for solid oxide cells. Hydrogen storage via compressed gas up to 70 MPa is optional for automobile applications. Fuel cells favor hydrogen fuel because of its superfast electrode kinetics. PEM fuel cells and solid oxide fuel cells are dominating technologies for automobile and stationary applications, respectively. Both technologies are at the threshold of their commercial markets with verified technical readiness and environmental merits; however, they still face restraints such as unavailable hydrogen fueling infrastructure, long-term durability, and costs to compete with the analog power technologies already on the market.

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This paper reviews the hydrogen technological chain in the framework of renewable energy, including water electrolysis, hydrogen storage, and fuel cell technologies. Fuel cell technologies are at the threshold of commercial markets with verified technical readiness, but still face limitations such as unavailable hydrogen infrastructure, durability, and competitive costs.