Multi-layer cathode block

A multi-layer cathode block (30) for an electrolytic cell (10) has at least a surface layer (32) with a surface expansion index and a second layer (34) with a second expansion index. The surface layer (32) includes a surface wetting agent in a first total amount. The second layer (34) includes a wetting agent in a second total amount. The surface layer (32) is directly superposed to the second layer (34). The second wetting agent in the second layer (34) includes metal boride precursors that react together to generate a metal boride component in situ when the cathode block (30) is exposed to start-up and operation conditions of the electrolytic cell (10). The second total amount is lower than the first total amount and is selected so as to minimize the difference between the expansion indexes of the surface layer (32) and the second layer (34).