To fully realize the commercial viability of Pt in fuel cells, the usage of scarce Pt must be reduced while the activity and durability in O₂ reduction reaction (ORR) must be enhanced. Here we report a metallic stack design achieving these goals for ORR, based on atomically precise materials synthesis. Au@Pd@Pt nanostructures with atomically thin Pt shells and high-index surfaces form an excellent platform for integrating the effects of electronic structures, surface facets, and substrate stabilization to boost ORR performance. Au@Pd@Pt trisoctahedrons (TOH) achieve mass activity 6.1 times higher than that of commercial Pt/C and dramatically enhanced durability beyond 1.0 V vs. a reversible hydrogen electrode in oxidation potential. Meanwhile, Pt comprises only 3.2% of the nanostructures. To further improve the ORR activity and demonstrate the versatility of our strategy, we implement the same design in PtNi alloy electrocatalysts. The Au@Pd@PtNi TOHs exhibit mass activity 14.3 times higher than that of commercial Pt/C as well as excellent durability. This work demonstrates an alternative strategy for fabricating high-performance and low-cost catalysts, and highlights the importance of simultaneous surface and interfacial engineering with atomic precision in designing catalysts.

The development of catalysts with high activity and durability for the cathodic oxygen reduction reaction (ORR) in both alkaline and acidic media is important for improving the performance of the proton exchange membrane (PEM) fuel cells. This can be achieved by dispersing Pt-based alloy nanoparticles inside N-doped porous carbon frameworks. However, it still requires the development of a facile method towards synthesizing this unique hybrid structure. In this work, we demonstrate that N-doped carbon-stabilized PtCo nanoparticles (PtCo@NC) can be facilely synthesized via thermal decomposition of Pt-incorporated Co-based zeolitic imidazolate framework (Pt@ZIF-67). The thickness of the carbon framework can be optimized to enable excellent durability, in sharp contrast to a commercial Pt/C catalyst. The mass activities achieved by optimizing the thickness of the carbon framework are 0.80 and 0.82 A·mg_Pt^–1 at 0.9 V vs. RHE in alkaline and acidic electrolytes, respectively, which are nearly 8 times greater than those of the Pt/C. This work provides an alternative approach to low-cost and high-performance catalysts for both alkaline and acidic fuel cells.

Formic acid oxidation is an important electrocatalytic reaction in proton-exchange membrane (PEM) fuel cells, in which both active sites and species adsorption/activation play key roles. In this study, we have developed hollow Pd-Ag alloy nanostructures with high active surface areas for application to electrocatalytic formic acid oxidation. When a certain amount of Ag is incorporated into a Pd lattice, which is already a highly active material for formic acid oxidation, the electrocatalytic activity can be significantly boosted. As indicated by theoretical simulations, coupling between Pd and Ag induces polarization charges on Pd catalytic sites, which can enhance the adsorption of HCOO^* species. As a result, the designed electrocatalysts can achieve reduced Pd usage and enhanced catalytic properties at the same time. This study represents an approach that simultaneously fabricates hollow structures to increase the number of active sites and utilizes interatomic interactions to tune species adsorption/activation towards improved electrocatalytic performance.

Cathodic oxygen reduction reaction (ORR) is a highly important electrochemical reaction in renewable-energy technologies. In general, the surface area, exposed facets and electrical conductivity of catalysts all play important roles in determining their electrocatalytic activities, while their performance durability can be improved by integration with supporting materials. In this work, we have developed a method to synthesize hybrid structures between PtPd bimetallic nanocages and graphene by employing selective epitaxial growth of single-crystal Pt shells on Pd nanocubes supported on reduced graphene oxide (rGO), followed by Pd etching. The hollow nature, {100} surface facets and bimetallic composition of PtPd nanocages, together with the good conductivity and stability of graphene, enable high electrocatalytic performance in ORR. The obtained PtPd nanocage-rGO structures exhibit mass activity (0.534 A·mg_Pt^-1) and specific activity (0.482 mA·cm^-2) which are 4.4 times and 3.9 times greater than the corresponding values for Pt/C.