Fuel cell

A fuel cell turns the chemical energy of a fuel — usually hydrogen — directly into electricity, without burning anything. Hydrogen and oxygen meet across a membrane in a quiet electrochemical reaction whose only by-products are electricity, heat and water. Because there is no combustion, a fuel cell running on clean hydrogen makes power at the point of use with no smoke and few moving parts.

Cities are mostly interested in fuel cells as clean, on-site generation for buildings and transport. On Tokyo Bay, the HARUMI FLAG district pipes pure hydrogen to fuel cells in each residential block, powering shared facilities for some 12,000 residents — Japan's first full-scale hydrogen infrastructure in a housing area. Toyota's Woven City is testing home fuel cells alongside robotics and autonomous mobility with its first residents. Feeding this generation into a building's smart grid lets an energy-management system lean on it at peak demand.

The honest catch is the fuel, not the cell. Most hydrogen today is made from natural gas, so the climate benefit depends entirely on where the hydrogen comes from; green hydrogen is still scarce and expensive. Fuel cells and hydrogen pipelines also cost far more than an ordinary grid connection — which is why the atlas holds only a couple of real city examples. Genuine deployments remain rare showcases, not standard infrastructure.