Efficient direct formic acid fuel cell (DFAFC) anode of nano-sized palladium complex: High durability and activity origin

•A novel nano-sized palladium-complex catalyst for DFAFCS is presented.•Nano-Pdcomplex exhibits outstanding activity and durability compared traditional Pd-based catalysts.•Nano-Pdcomplex bulky structure hindering the agglomeration and poisoning of the Pd active sites.•Cis-form of the Nano-Pdcomplex with a square planar structure is totally inactive for FAO.•Trans-structure with a tetrahedral geometry is highly active for FAO.

The low stability of Pd-based catalysts extremely obstructs their applied application in the direct formic acid fuel cells (DFAFCs). Herein, a novel nano-sized palladium-complex (nano-Pdcomplex) with outstanding performance (activity and durability) for DFAFCs anodic reaction (Formic acid oxidation; FAO) compared to the commercial Pd-based catalysts is introduced. Morphologically, nano-sized Pd-complex shows an intersected nano-rod like structure with an average particle size ca. 17 nm. Electrochemically, nano-Pdcomplex modified GC electrode (Nano-Pdcomplex/GC) has 12 times higher electrocatalytic activity, 8.0 times higher electrochemical active surface area, 3.0 times higher catalyst utilization, and ca., 16 times higher stability after 5.0 h than that of traditional Pd nanoparticles modified GC electrode (PdNPs/GC) with the same Pd loading. This significant enhancement in both activity and stability is attributed to nano-Pdcomplex bulky structure hindering the agglomeration of the Pd active sites and inhibiting the adsorption of poisoning CO-like intermediate species. DFT studies shows that nano-Pdcomplex has two different geometries: (a) cis-structure which has a square planar geometry and it is inactive for FAO, and (b) trans-structure with a tetrahedral geometry and it is highly active for FAO. This study introduces a new promising category of Pd-based catalyst with high activity, catalyst utilization and durability for DFAFCs applications.

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