Novel (Ir,Sn,Nb)O2 anode electrocatalysts with reduced noble metal content for PEM based water electrolysis

A solid solution of IrO2, SnO2 and NbO2, denoted as (Ir,Sn,Nb)O2, of compositions (Ir1−2xSnxNbx)O2 with x = 0, 0.125, 0.20, 0.25, 0.30, 0.35, 0.40, 0.425 and 0.50 has been synthesized by thermal decomposition of a homogeneous mixture of IrCl4, SnCl2·2H2O and NbCl5 ethanol solution coated on pretreated Ti foil. The (Ir,Sn,Nb)O2 thin film of different compositions coated on Ti foil has been studied as a promising oxygen reduction anode electrocatalyst for PEM based water electrolysis. It has been identified that (Ir,Sn,Nb)O2 of composition up to x = 0.30 [(Ir0.40Sn0.30Nb0.30)O2] shows similar electrochemical activity compared to pure IrO2 (x = 0) resulting in ∼60 mol.% reduction in noble metal content. On the other hand, (Ir,Sn,Nb)O2 of composition x = 0.20 [(Ir0.20Sn0.40Nb0.40)O2] shows only 20% lower activity compared to pure IrO2 though the noble metal oxide, IrO2 loading is reduced by 80 mol.%. The accelerated life test of the anode electrocatalyst for 48 h followed by elemental analysis of the electrolyte shows that (Ir,Sn,Nb)O2 improves the stability of the electrode in comparison to pure IrO2 electrocatalyst in oxygen reduction processes. The excellent electrochemical activity as well as long term structural stability of (Ir,Sn,Nb)O2 during water electrolysis has been discussed using first-principles calculations of the total energies, electronic structures, and cohesive energies of the model systems.