The world is on a collision course with a climate crisis. And yet, the global economy still relies heavily on fossil fuels – the main source of anthropogenic greenhouse gas emissions. These fuels are convenient because they provide high-energy density and can easily be transported over long distances. To achieve net zero emissions by 2050 and stabilize the climate, countries are seeking cleaner alternatives. Electricity produced from renewable energy sources – such as wind, solar and hydropower – will be critical in the bid to replace fossil fuels. However, some end-uses require an energy vector with characteristics that electrons cannot deliver.