Electrochemical reaction unit and fuel cell stack

An electrochemical reaction unit comprising:

• a single cell including an electrolyte layer containing solid oxide, and a cathode and an anode which face each other in a first direction with the electrolyte layer intervening therebetween;
• a current collector disposed on a cathode side of the single cell and having a protrusion protruding toward the cathode;
• an electrically conductive coat covering a surface of the current collector;
• and
• an electrically conductive bonding layer bonding the cathode and the protrusion covered with the coat;
• the electrochemical reaction unit being characterized in that in at least one section of the protrusion taken in parallel with the first direction, the protrusion covered with the coat has a covered portion covered with the bonding layer and an exposed portion exposed from the bonding layer and including a corner portion of the protrusion covered with the coat.