From their website:

Using the same airframe and overall architecture as Joby’s core, battery-electric aircraft, this demonstrator features a liquid hydrogen fuel tank, designed and built by Joby, which stores up to 40 kilograms of liquid hydrogen, alongside a reduced mass of batteries. Hydrogen is fed into a fuel cell system, designed and built by H2FLY, to produce electricity, water, and heat. The electricity produced by the hydrogen fuel cell powers the six electric motors on the Joby aircraft, with the batteries providing additional power primarily during take-off and landing.

I'd love to hear what it was like trying to refuel this thing. Even space companies tend to avoid LH2 because it's so picking awful to work with.