EXAFS analysis of Pd atomic clusters

Atomic Dispersion and Surface Enrichment of Palladium in Nitrogen-Doped Porous Carbon Cages Lead to High-Performance Electrocatalytic Reduction of Oxygen

Metal-nitrogen-carbon (MNC) nanocomposites have been hailed as promising and efficient electrocatalysts toward oxygen reduction reaction (ORR), due to the formation of MN_x coordination moieties. However, MNC hybrids are mostly prepared by pyrolysis of organic precursors along with select metal salts, where part of the MN_x sites are inevitably buried in the carbon matrix. This limited accessibility compromises the electrocatalytic performance. Herein, we describe a wet-impregnation procedure by facile thermal refluxing, whereby palladium is atomically dispersed and enriched onto the surface of hollow, nitrogen-doped carbon cages (HNC) forming Pd-N coordination bonds. The obtained Pd-HNC nanocomposites exhibit an ORR activity in alkaline media markedly higher than that of metallic Pd nanoparticles, and the best sample even outperforms commercial Pt/C and relevant Pd-based catalysts reported in the literature. The results suggest that atomic dispersion and surface enrichment of palladium in a carbon matrix may serve as an effective strategy in the fabrication of high-performance ORR electrocatalysts.

Manufacturing and characterization of Pd nanoparticles formed on immobilized bacterial cells

AIMS

To fabricate and analyse Pd nanoparticles on immobilized bacterial cells.

METHODS AND RESULTS

Biological ceramic composites (biocers) were used as a template to produce Pd(0) nanoparticles. The metal-binding cells of the uranium mining waste pile isolate, Bacillus sphaericus JG-A12 were used as a biological component of the biocers and immobilized by using sol-gel technology. Vegetative cells and surface-layer proteins of this strain are known to bind high amounts of Pd(II) that can be reduced to Pd(0) particles by the addition of a reducing agent. Sorption of Pd(II) by the biocers from a metal complex solution was studied by inductively coupled plasma mass spectroscopy analyses. After embedding into sol-gel ceramics, the cells retained their Pd(II)-binding capability. Pd(0) nanoclusters were produced by the addition of hydrogen as reducing agent after the sorption of Pd(II). The interactions of Pd(0) with the biocers and the formed Pd(0) nanoparticles were investigated by extended X-ray absorption fine structure spectroscopy. The particles had a size of 0.6-0.8 nm.

CONCLUSIONS

Bacterial cells that were immobilized by embedding into sol-gel ceramics were used as a template to produce Pd nanoclusters of a size smaller than 1 nm. These particles possess interesting physical and chemical properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of embedded bacterial cells as template enabled the fabrication of immobilized Pd(0) nanoparticles. These particles are highly interesting for technical applications, such as the development of novel catalysts.