Hydrogen concentration sensor

A fuel cell power plant, comprising:

• a fuel cell stack;
• a reformer configured to produce hydrogen fuel for the fuel cell stack;
• a hydrogen concentration sensor that detects hydrogen concentration in a hydrogen fuel supplied in a supply line to the fuel cell stack;
• and
• a controller that is configured to dynamically adjust operation of the reformer such that the reformer produces hydrogen fuel that is supplied in the supply line to the fuel cell stack based, at least in part, on an indication from the hydrogen concentration sensor,
• the hydrogen concentration sensor comprising:
• a hydrogen chamber configured to isolate hydrogen within the hydrogen chamber from gas outside the hydrogen chamber;
• a hydrogen evolving electrode configured to generate pure hydrogen within the hydrogen chamber;
• a reference electrode situated to be exposed to the pure hydrogen within the hydrogen chamber;
• and
• a detection electrode associated with the reference electrode, the detection electrode being situated to be exposed to the gas outside the hydrogen chamber, the detection electrode being configured to provide an indication of a concentration of hydrogen in the gas outside the hydrogen chamber,
• wherein
• the hydrogen evolving electrode is part of a first electrochemical cell,
• the reference electrode and the detection electrode are part of a second electrochemical cell,
• the first electrochemical cell includes a first matrix containing a liquid electrolyte,
• the second electrochemical cell includes a second matrix containing a liquid electrolyte, and
• the first and second electrochemical cells are disposed on a common side of the hydrogen chamber and are separated by a gap established by a wall that protrudes into the hydrogen chamber to establish a constriction between a first region of the hydrogen chamber associated with the hydrogen evolving electrode and a second region of the hydrogen chamber associated with the reference electrode.