An international team of researchers has synthesized one-dimensional bunched platinum-nickel (Pt-Ni) alloy nanocages with a Pt-skin structure for the oxygen reduction reaction in fuel cells. The nanocages display high mass activity (3.52 amperes per milligram platinum) and specific activity (5.16 milliamperes per square centimeter platinum)—nearly 17 and 14 times higher respectively as compared with a commercial platinum on carbon (Pt/C) catalyst. A paper on their work is published in Science.

The catalyst exhibits high stability with negligible activity decay after 50,000 cycles. Experimental results and theoretical calculations reveal the existence of fewer strongly bonded platinum-oxygen (Pt-O) sites induced by the strain and ligand effects.

The fuel cell supported by this catalyst delivers a current density of 1.5 amperes per square centimeter at 0.6 volts and can operate steadily for at least 180 hours.

Platinum (Pt) is the most active electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries with promising stability. Nevertheless, the state-of-the-art Pt catalysts still lack activity and stability with respect to the cost and availability for large-scale commercial implementation.

Engineering the near-surface composition of nanostructured Pt alloys represents one promising approach to enhance the electrocatalytic performance of Pt-based electrocatalysts, in which the exposure of highly active sites with optimum performance can be maximized.

Adding other transition metals can enhance the catalytic performance via ligand and strain effects through modifying the binding strength of Pt-oxygen intermediates. The introduction of open nanostructures, including hollow and porous nanoparticles such as nanocages (NCs) and nanoframes, may help in achieving this goal and also enhance mass transfer.

—Tian et al.

To prepare the nanocages, the team first prepared 1D Pt-Ni bunched nanospheres (BNSs) by reducing Pt and Ni precursors with varying ratios by a one-pot solvothermal method. Treatment under acidic conditions selectively removed Ni species to leave 1D Pt-Ni BNCs with ultrathin walls composed of a platinum skin and a residual platinum-nickel alloy below this skin.

Schematic illustration of the preparation of Pt-Ni BNCs. Tian et al.

This work provides an effective strategy for the rational design of Pt alloy nanostructures and will help guide the future development of catalysts for their practical applications in energy conversion technologies and beyond.

—Tian et al.

Resources

• Xinlong Tian, Xiao Zhao, Ya-Qiong Su, Lijuan Wang, Hongming Wang, Dai Dang, Bin Chi, Hongfang Liu, Emiel J.M. Hensen, Xiong Wen (David) Lou, Bao Yu Xia (2019) “Engineering bunched Pt-Ni alloy nanocages for efficient oxygen reduction in practical fuel cells” Science Vol. 366, Issue 6467, pp. 850-856 doi: 10.1126/science.aaw7493