High Oxygen Reduction Reaction Performances of Cathode Materials Combining Polyoxometalates, Coordination Complexes, and Carboneous Supports

A series
of carbonaceous-supported precious-metal-free polyoxometalate
(POM)-based composites which can be easily synthesized on a large
scale was shown to act as efficient cathode materials for the oxygen
reduction reaction (ORR) in neutral or basic media via a four-electron
mechanism with high durability. Moreover, exploiting the versatility
of the considered system, its activity was optimized by the judicious
choice of the 3d metals incorporated in the {(PW9)2M7} (M = Co, Ni) POM core, the POM counterions
and the support (thermalized triazine-based frameworks (TTFs), fluorine-doped
TTF (TTF-F), reduced graphene oxide, or carbon Vulcan XC-72. In particular,
for {(PW9)2Ni7}/{Cu­(ethylenediamine)2}/TTF-F, the overpotential required to drive the ORR compared
well with those of Pt/C. This outstanding ORR electrocatalytic activity
is linked with two synergistic effects due to the binary combination
of the Cu and Ni centers and the strong interaction between the POM
molecules and the porous and highly conducting TTF-F framework. To
our knowledge, {(PW9)2Ni7}/{Cu­(ethylenediamine)2}/TTF-F represents the first example of POM-based noble-metal-free
ORR electrocatalyst possessing both comparable ORR electrocatalytic
activity and much higher stability than that of Pt/C in neutral medium.