"Core-Shell" ORR Nano-Electrocatalysts Based on a PtNi Carbon Nitride "Shell" and Cu NP "Core"

One of the most severe bottlenecks in the operation of proton exchange membrane fuel cells (PEMFCs) is the sluggish kinetics of the Oxygen Reduction Reaction (ORR). Thus, suitable ORR electrocatalysts are required in order to obtain PEMFCs able to yield a sufficiently high performance [1]. State-of-the-art ORR electrocatalysts for application in PEMFCs are obtained by supporting Pt nanocrystals on active carbon supports characterized by a very large surface area [2]. However, despite extensive investigations the performance of these electrocatalysts does not meet yet the strict requirements necessary for a large-scale application of PEMFC technology. A new preparation protocol has been proposed recently to obtain nano-electrocatalysts with a well-controlled chemical composition, based on the pyrolysis and activation of hybrid inorganic-organic precursors. The resulting carbon nitride nano-electrocatalysts thus prepared show an outstanding ORR performance both in “ex-situ” studies and in a single-cell configuration [3]. In this work, a new family of multimetal carbon nitride nano-electrocatalysts is described. The materials are synthesized by pyrolysis of a hybrid inorganic-organic precursor including Pt and Ni atoms impregnating Cu nanoparticles acting as the support. The final ORR electrocatalysts are obtained after an extensive electrochemical dealloying activation process. The products are fully characterized before and after the activation processes. The chemical composition of the electrocatalysts is determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and microanalysis. The morphology is investigated by High-Resolution Scanning Electron Microscopy (HR-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). The structure is probed by powder X-Ray Diffraction (XRD). The electrochemical performance of the electrocatalysts in the ORR is determined both by “ex-situ” measurements carried out by cyclic voltammetry with the rotating ring disk electrode (CV-TF-RRDE method) and by “in-situ” fuel cell studies in a PEM single-cell configuration. Preliminary results indicate clearly that the proposed electrocatalysts show a remarkable ORR performance, which is significantly enhanced in comparison with the Pt/C reference both in terms of overpotential and selectivity in the 4-electron mechanism of the ORR (see Figure 1).

REFERENCES

[1] J. X. Wang, F. A. Uribe, T. E. Springer, J. Zhang, R. R. Adzic, Faraday Discuss. 140, 347 (2008).

[2] J. Zhang, Front. Energy 5, 137 (2011).

[3] V. Di Noto, E. Negro, Electrochim. Acta 55, 7564 (2010).