Defective nanomaterials for electrocatalysis oxygen reduction reaction.

The difficulties in O2 molecule adsorption/activation, the cleavage of the O-O bond, and the desorption of the reaction intermediates at the surface of the electrodes make the cathodic oxygen reduction reaction (ORR) for fuel cells show extremely sluggish kinetics. Thus, it is important to the exploitation of highly active and stable electrocatalysts for the ORR to promote the performance and commercialization of fuel cells. Many studies have found that the defects affect the electron and the geometrical structure of the catalyst. The catalytic performance is enhanced by constructing defects to optimize the adsorption energy of substrates or intermediates. Unfortunately, still many issues are poorly recognized, such as the effect of defects (types, contents, and locations) in catalytic performance is unclear, and the catalytic mechanism of defective nanomaterials is lacking. In this review, the defective electrocatalysts divided into noble and non-noble metals for the ORR are highlighted and summarized. With the assistance of experimental results and theoretical calculations, the structure-activity relationships between defect engineering and catalytic performance have been clarified. Finally, after a deeper understanding of defect engineering, a rational design for efficient and robust ORR catalysts for PEMFCs is further guided.

Controlled synthesis of single cobalt atom catalysts via a facile one-pot pyrolysis for efficient oxygen reduction and hydrogen evolution reactions.

Metal-nitrogen doped carbon catalysts (M-N/C) with abundantly accessible M-Nx sites, particularly single metal atom M-N/C (SAM-N/C), have been developed as a substitute for expensive Pt-based catalysts. These catalysts are used to increase the efficiency of otherwise sluggish oxygen reduction reactions (ORR) and hydrogen evolution reactions (HER). However, although the agglomerated metal nanoparticles are usually easy to form, they are very difficult to remove due to the protective surface-coating carbon layers, a factor that significantly hampers SAM-N/C fabrication. Herein, we report a one-step pyrolysis approach to successfully fabricate single cobalt atom Co-N/C (SACo-N/C) by using a Co2+-SCN- coordination compound as the metal precursor. Thanks to the decomposition of Co2+-SCN- compound at lower temperature than that of carbon layer deposition, Co-rich particles grow up to larger ones before carbon layers formation. Even though encapsulated by the carbon layers, it is difficult for the large Co-rich particle to be completely sealed. And thus, it makes the Co atoms possible to escape from incomplete carbon layer, to coordinate with nitrogen atoms, and to form SACo-N/C catalysts. This SACo-N/C exhibits excellent performances for both ORR (half-wave potential of 0.878 V) and HER (overpotential at 10 mA/cm2 of 178 mV), and is thus a potential replacement for Pt-based catalysts. When SACo-N/C is integrated into a Zn-O2 battery, battery with high open-circuit voltage (1.536 V) has high peak power density (266 mW/cm2) and large gravimetric energy density (755 mA h/gZn) at current densities of 100 mA/cm2. Thus, we believe that this strategy may offer a new direction for the effective generation of SAM-N/C catalysts.

Inert V2O3 oxide promotes the electrocatalytic activity of Ni metal for alkaline hydrogen evolution.

Here, we develop inert V2O3 oxide to enhance the HER activity of industrial Ni catalysts with the assistance of abundant metal/oxide interfaces. The as-synthesized Ni/V2O3 catalyst exhibits over 5 times the activity of a pure Ni sample due to the particle size control and metal/oxide interaction, and excellent durability as a result of oxide anchoring.