Cada mañana en una instalación de tránsito en Canton, Ohio, más de una docena de autobuses se detienen en una estación de servicio antes de partir hacia sus rutas en esta ciudad al sur de Cleveland.

Los autobuses, fabricados por El Dorado National y propiedad de la Autoridad de Tránsito Regional del Área de Stark, se parecen a cualquier otro. Sin embargo, colectivamente, reflejan la vanguardia de una tecnología que podría desempeñar un papel clave en la producción de un transporte interurbano más limpio. En lugar del combustible diésel que eructa la contaminación, una cuarta parte de los autobuses de la agencia funcionan con hidrógeno. No emiten más que vapor de agua inofensivo.

El hidrógeno, el elemento más abundante en el universo, se considera cada vez más, junto con los vehículos eléctricos, como una forma de frenar el impacto ambientalmente destructivo de los 1200 millones de vehículos del planeta, la mayoría de los cuales queman gasolina y diésel. Los fabricantes de camiones grandes y vehículos comerciales están comenzando a adoptar las tecnologías de celdas de combustible de hidrógeno como un camino a seguir. También lo son los fabricantes de aviones, trenes y vehículos de pasajeros.

El transporte es el mayor contribuyente de EE. UU. al cambio climático, razón por la cual la energía del hidrógeno, a largo plazo, se considera una forma potencialmente importante de ayudar a reducir las emisiones de carbono.

Sin duda, el hidrógeno está lejos de ser una solución mágica. Por ahora, el hidrógeno que se produce a nivel mundial cada año, principalmente para las refinerías y la fabricación de fertilizantes, se produce a partir de gas natural o carbón. Ese proceso contamina el aire, calentando el planeta en lugar de salvarlo. De hecho, un nuevo estudio realizado por investigadores de las universidades de Cornell y Stanford descubrió que la mayor parte de la producción de hidrógeno emite dióxido de carbono, lo que significa que el transporte impulsado por hidrógeno aún no puede considerarse energía limpia.

Sin embargo, los defensores del transporte impulsado por hidrógeno dicen que, a largo plazo, la producción de hidrógeno está destinada a ser más segura para el medio ambiente. Ellos prevén un uso creciente de la electricidad de la energía eólica y solar, que puede separar el hidrógeno y el oxígeno en el agua. A medida que estas formas renovables de energía obtengan un uso más amplio, la producción de hidrógeno debería convertirse en un proceso más limpio y menos costoso.

Dentro de tres años, General Motors, Navistar y la empresa de camiones J.B. Hunt planean construir estaciones de servicio y operar camiones de hidrógeno en varias autopistas de EE. UU. Toyota, Kenworth y el Puerto de Los Ángeles han comenzado a probar camiones de hidrógeno para transportar mercancías desde los barcos hasta los almacenes.

Volvo Trucks, Daimler Trucks AG y otros fabricantes también han anunciado asociaciones. Las empresas esperan comercializar su investigación, ofreciendo camiones de cero emisiones que ahorren dinero y cumplan con regulaciones de contaminación más estrictas.

En Alemania, un tren propulsado por hidrógeno comenzó a operar en 2018, y están llegando más. Airbus, con sede en Francia, el fabricante de aviones de pasajeros más grande del mundo, también está considerando el hidrógeno.

"Esto es lo más cerca que nos hemos visto llegar hasta ahora a ese punto de inflexión real", dijo Shawn Litster, profesor de ingeniería mecánica en la Universidad Carnegie Mellon que ha estudiado las celdas de combustible de hidrógeno durante casi dos décadas.

El hidrógeno ha sido durante mucho tiempo una materia prima para la producción de fertilizantes, acero, petróleo, hormigón y productos químicos. También ha estado operando vehículos durante años:alrededor de 35,000 montacargas en los Estados Unidos, alrededor del 4% del total de la nación, funcionan con hidrógeno. Its eventual use on roadways, to haul heavy loads of cargo, could begin to replace diesel-burning polluters.

No one knows when, or even whether, hydrogen will be adopted for widespread use. Craig Scott, Toyota's head of advanced technology in North America, says the company is perhaps two years from having a hydrogen truck ready for sale. Building more fueling stations will be crucial to widespread adoption.

Kirt Conrad, CEO of Canton's transit authority since 2009, says other transit systems have shown so much interest in the technology that SARTA takes its buses around the country for demonstrations. Canton's system, which bought its first three hydrogen buses in 2016, has since added 11. It's also built a fueling station. Two California transit systems, in Oakland and Riverside County, have hydrogen buses in their fleets.

"We've demonstrated that our buses are reliable and cost-efficient, and as a result, we're breaking down barriers that have slowed wider adoption of the technology," Conrad said.

The test at the Port of Los Angeles started in April, when the first of five semis with Toyota hydrogen powertrains began hauling freight to warehouses in Ontario, California, about 60 miles away. The $82.5 million public-private project eventually will have 10 semis.

Hydrogen fuel is included in President Joe Biden's plans to cut emissions in half by 2030. The infrastructure bill the Senate approved passed this week includes $9 billion for research to reduce the cost of making clean hydrogen, and for regional hydrogen manufacturing hubs.

The long-haul trucking industry appears to be the best bet for early adoption of hydrogen. Fuel cells, which convert hydrogen gas into electricity, provide a longer range than battery-electric trucks, fare better in cold weather and can be refueled much faster than electric batteries can be recharged. Proponents say the short refueling time for hydrogen vehicles gives them an edge over electric vehicles for use in taxis or delivery trucks, which are in constant use.

That advantage was important for London-based Green Tomato Cars, which uses 60 hydrogen fuel cell-powered Toyota Mirai cars in its 500-car zero emission fleet to transport corporate customers. Co-founder Jonny Goldstone said his drivers can travel over 300 miles (500 kilometers) on a tank and refuel in three minutes.

Because drivers' earnings depend on fares, Goldstone said, "if they have to spend 40, 50 minutes, an hour, two hours plugging a car in in in the middle of the working day, that for them is just not acceptable."

For now, Green Tomato is among the largest operators of hydrogen vehicles in what is still a tiny market in Europe, with about 2,000 fuel cell cars, garbage trucks and delivery vans on the roads.

About 7,500 hydrogen fuel cell cars are on the road in the U.S., mostly in California. Toyota, Honda and Hyundai produce the cars, which are priced thousands more than gasoline-powered vehicles. California has 45 public fueling stations, with more planned or under construction.

Unlike with buses and heavy trucks, experts say the future of passenger vehicles in the U.S. lies mainly with electric battery power, not hydrogen. Fully electric vehicles can travel farther than most people need to go on a relatively small battery.

And for now, hydrogen production is adding to rather than reducing pollution. The world produces about 75 million tons a year, most of it in a carbon emission-creating processes involving steam reformation of natural gas. China uses higher-polluting coal.

So-called "blue" hydrogen, made from natural gas, requires an additional step. Carbon dioxide emitted in the process is sent below the earth's surface for storage. The Cornell and Stanford study found that manufacturing blue hydrogen emitted 20% more carbon than burning natural gas or coal for heat.

That's why industry researchers are focused on electrolysis, which uses electricity to separate hydrogen and oxygen in water. Hydrogen mixes with oxygen in a vehicle's fuel cell to produce power. The amount of electricity generated by wind and solar is growing worldwide, making electrolysis cleaner and cheaper, said Joe Cargnelli, director of hydrogen technologies for Cummins, which makes electrolyzers and fuel cell power systems.

Currently, it costs more to make a hydrogen truck and produce the fuel than to put a diesel-powered truck on the road. Hydrogen costs about $13 per kilogram in California, and 1 kilogram can deliver slightly more energy than a gallon of diesel fuel. By contrast, diesel fuel is only about $3.25 per gallon in the U.S.

But experts say that disparity will narrow.

"As they scale up the technology for production, the hydrogen should come down," said Carnegie Mellon's Litster.

While a diesel semi can cost around $150,000 depending on how it's equipped, it's unclear how much fuel cell trucks would cost. Nikola, a startup electric and hydrogen fuel cell truck maker, estimated last year that it would receive about $235,000 for each hydrogen semi it sells.

Clean electricity might eventually be used to make and store hydrogen at a rail yard, where it could refuel locomotives and semis, all with zero emissions.

Cummins foresees the widespread use of hydrogen in the U.S. by 2030, sped by stricter diesel emissions regulations and government zero-emissions vehicle requirements. Already, Europe has set ambitious green hydrogen targets designed to accelerate its use.

"That's just going to blow the market open and kind of drive it," Cargnelli said. "Then you'll see other places like North America kind of follow suit."