sweet spot for ceramic fuel cells, page-4

The 91% quoted for the hydrogen SOFC was combined electrical and heat efficiency. No doubt the electrical efficiency would be below CFU's 60% (perhaps considerably so) meaning a lot of the efficiency is in heat recovery. Good if you need lots of heat. Not so good if you don't.

There are lots of problems with using pure hydrogen. The gas is not particularly compressible. It has a wide flammable range in air (~4% to ~78% hydrogen to air ratio) and a very low ignition energy (ie it is very dangerous!). It also causes hydrogen embrittlement in many metals and alloys, meaning specialist piping is required (and not cheap).

Natural gas and LPG is the way to go.