A method of catalytic ammonia decomposition, where the method includes: flowing ammonia into a reactor charged with a supported medium entropy metal alloy (MEA) catalyst including MEA particles supported on a support, the MEA particles including a first principal metal, a second principal metal, and a third principal metal, where each of the principal metals is independently selected without repetition from the group consisting of Co, Cr, Fe, Mn, Ni, Al, Cu, Zn, Ti, Zr, Mo, V, Ru, Rh, Pd, Ag, W, Re, Ir, Pt, Au, Ce, Y, Yb, Sn, Ga, In, and Be; and catalytically decomposing the ammonia into hydrogen and nitrogen over the supported MEA catalyst in the reactor at a reaction temperature between 200 C. and 900 C.