1.5‐diaza‐3.7‐diphosphacyclooсtane bis‐ligand nickel(II) complexes as oxygen reduction catalysts for proton exchange membrane fuel cells

Membrane electrode assemblies (MEAs) with 1,5-diaza-3,7-diphosphacyclootane organometallic bis-ligand nickel(II) complexes [Ni((P2N2Ph)-N-Ph)(2)](2+)2(.)[BF4](-) [1(Ph-Ph)] and [Ni((P2N2Bn)-N-Ph)(2)](2+)2(.)[BF4](-) [2(Ph-Bn)] as a part of oxygen reduction reaction (ORR) catalysts for proton-exchange membrane fuel cells (PEMFCs) are built and tested. The complexes are characterized by atomic force microscopy (AFM), electron spin resonance (ESR), cyclic voltammetry (CV), and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). Electrochemical activity toward ORR and catalytic stability of compounds is tested by chronoamperometry (CA). The electrochemical activity of catalysts and ORR mechanisms is studied by rotating disk electrode (RDE). A performance analysis of the PEMFC is carried out. A peak power density of about 11.84 mW cm(-2) and a current density of 80 mA cm(-2) are measured for 2(Ph-Bn)/C cathode and Pt/C anode catalysts, respectively. Chronoamperometric tests in 0.5 m H2SO4 for 3 h show an excellent stability for the compound 2(Ph-Bn). The performance of 1(Ph-Ph)/C catalyst and the chronoamperometric stability of 1(Ph-Ph) are worse. A possible relationship between the catalysts' performance and basicity of pendant amines on the base of the proposed ORR mechanism with two metal centers is discussed.