Airbus has unveiled three visual concepts for ”zero emission” airplanes to be powered by hydrogen. It is the planemaker’s latest effort to draw public attention to its ”zero-emission” ambitions as European governments push for cleaner technology in their post-COVID recovery plans.

Airbus has set itself a deadline of 2035 to put a carbon-free commercial aircraft into service, a target engine makers like Safran have described as ambitious. The ”ZEROe” initiative includes concepts for two conventional-looking aircraft: a turbofan jet engine able to carry 120-200 people over 2,000 nautical miles (3,700 km) and a turboprop able to carry up to 100 people for 1,000 nm.

Unlike normal planes, the engines would be adapted to burn liquid hydrogen stored in the rear fuselage. A third proposal incorporates a revolutionary ”blended wing body” design similar to one presented in February.

At the same time, Airbus is working on a demonstrator, with initial results expected in 2021. ”The demonstrator will allow us to assess what the most promising architecture is,” Airbus Chief Technology Officer Grazia Vittadini said in an interview. ”We see it as applicable to all Airbus products eventually.”

To meet its 2035 goal, Airbus would need to select technologies by 2025, she said. Other industry executives said such a clean break in propulsion could take until 2040. Challenges include finding ways to safely store volatile liquid hydrogen during flight at very cold temperatures.

Airbus dismissed concerns that hydrogen would be unsafe and has called for massive investment in new energy infrastructure. While hydrogen has been discussed since the 1970s, it remains too expensive for widespread use. Proponents say infrastructure investment and rising demand will lower the cost.

Most hydrogen used today is extracted from natural gas, which creates carbon emissions. However, Airbus said the hydrogen used for aviation would be produced from renewable energy and extracted from water with electrolysis. That’s a carbon-free process if powered by renewable electricity, but it is currently more expensive.