Hydrogen planes

Current issue of AW&ST devoted to Hydrogen in Aviation.
https://aviationweek.com/awst_current


On Sun, 27 Sep 2020 23:48:10 -0400, JF Mezei
wrote:

Before you scream this isn't space related...

Airbus announced a project to study hydrogen powered airplanes.
Basically tune current jet engines to burn H2 instead of kerosene, and
run fuel cells to supply plane with electricity.

Currently, there are spinning generators attached to the jet engines to
produce electricity.


Question: are fuel cells more efficient at producing electricity than
using mechanical power from a jet engine to drive a generator?

Since the Shuttle only had spinning turbines for 8 minutes of a flight
out of a 14 day trip, it made sense to have fuel cells, especially since
the water served the crew as well.

But for an aircraft where the jet engines kinda have to spin for the
whole flight, I am curious if diverting H2 to fuel cells is more
efficient than sending to engines to spin some more to drive generators.

Can fuel cells run off air, or do they need LOX to mix with LH2 to
produce power?