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including sustainable fuel cells and next-generation metal-air batteries. [1][2][3][4][5][6] Unfortunately, the complex reaction pathways and intrinsically sluggish reaction kinetics of the ORR predominantly limit the overall efficiency of energy conversion. Although platinum (Pt) and its alloys have been recognized as the most efficient ORR electrocatalysts to date, some critical issues, including the ever-increasing cost, scarce reserve, fuel crossover, and unsatisfactory durability of Pt, pose a severe challenge toward the widespread commercialization for these electrochemical energy devices. [7][8][9][10][11][12] In this regard, it is of great significance and highly imperative to explore Pt-free alternative electrocatalysts with superior activity and excellent durability, as well as low cost. Fortunately, the less expensive and more abundant palladium (Pd) nanostructures represent a class of promising and reliable ORR electrocatalysts with comparable or even superior electrocatalytic performances than Pt-based catalysts. [13][14][15][16][17][18][19] Moreover, incorporation of Pd with a secondary earth-abundant 3d-transition metal (TM) to form Pd-TM bimetallic alloy can not only further reduce the consumption of precious Pd, but also effectively modify the electronic structure of Pd, which often leads to extraordinary electrocatalytic properties, such as enhanced superior activity, high selectivity, and sufficient stability, which are inaccessible by the monometallic counterparts or physical mixture. [14,15,20,21] Among various 3d-transition metals, Ni has been identified as a promising candidate to form Pd-Ni alloys with excellent catalytic performances due to its relatively cheap price and the elaborate synergy between Ni and Pd. [14,[22][23][24] As such, PdNi bimetallic nanoalloys are considered to be a highly economical and efficient ORR electrocatalyst.On the other hand, construction of 3D networked nanostructures with hierarchical porosity, i.e., mesopores connected with macropores, also provides an effective strategy to improve the utilization efficiency of noble metal atoms and structural robustness of a noble metal-based nanocatalyst. Such unique structural feature could endow the catalyst with several fantastic properties which are distinct from the solid counterparts, including high surface area, low density, metallic backbone, excellent molecular accessibility, minimized mass diffusive Cost-effective electrocatalysts for the oxygen reduction reaction (ORR) play pivotal roles in energy conversion and storage processes. Designing a 3D networked bimetallic nanostructure with hierarchical porosity represents a reliable and effective strategy for the advancement of electrocatalysts with greatly improved activity and stability. However, it still remains a tremendous challenge in fabricating such fantastic nanostructure via a feasible and economical approach. Herein, a facile cyanogel-bridged synthetic strategy is demonstrated to fabricate PdNi 3D nanocorals with hierarchical porosity. The elaborate inte...

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Catalysts for the oxygen reduction reaction (ORR) play an important role in fuel cells. Alternative non-precious metal catalysts with comparable ORR activity to Pt-based catalysts are highly desirable for the development of fuel cells. In this work, we report for the first time a spinel MnCo 2 O 4 /C ORR catalyst consisting of uniform MnCo 2 O 4 nanoparticles cross-linked with two-dimensional (2D) porous carbon nanosheets (abbreviated as porous MnCo 2 O 4 /C nanosheets), in which glucose is used as the carbon source and NaCl as the template. The obtained porous MnCo 2 O 4 /C nanosheets present the combined properties of an interconnected porous architecture and a large surface area (175.3 m 2 ·g −1 ), as well as good electrical conductivity (1.15  10 2 S·cm −1 ). Thus, the as-prepared MnCo 2 O 4 /C nanosheets efficiently facilitate electrolyte diffusion and offer an expedite transport path for reactants and electrons during the ORR. As a result, the as-prepared porous MnCo 2 O 4 /C nanosheet catalyst exhibits enhanced ORR activity with a higher onset potential and current density than those of its counterparts, including pure MnCo 2 O 4 , carbon nanosheets, and Vulcan XC-72R carbon. More importantly, the porous MnCo 2 O 4 /C nanosheets exhibit a comparable electrocatalytic activity but superior stability and tolerance toward methanol crossover effects than a high-performance Pt/C catalyst in alkaline medium. The synthetic strategy outlined here can be extended to other nonprecious metal catalysts for application in electrochemical energy conversion.

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