Europe’s two biggest industrial and economic powers are laying billions on the table in an attempt to take on China in developing a “green” hydrogen sector to replace fossil fuels—but the continent’s top motor groups are wary of going along for the ride.

“You won’t see any hydrogen usage in cars,” said Volkswagen chief executive Herbert Diess.

The idea of a big market for vehicles powered by hydrogen fuel cells is “very optimistic,” according to Diess, who has overseen a €35 billion push into electric cars. “Not even in 10 years,” he told the Financial Times, “because the physics behind it are so unreasonable.”