Nanostructure Engineering of Metal-Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst.

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec-1, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices.

Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells.

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm-2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.