Highly coordinated Pd overlayers on nanoporous gold for efficient formic acid electro-oxidation

Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells. Based on in-depth theoretical calculations, here we demonstrate that surface Pd atoms with high coordination numbers (HCNs) can effectively modulate their adsorption energies for CO and OH, and thus achieve very high performance for formic acid electro-oxidation reaction (FAOR). Based on epitaxial coating Pd atomic layers onto nanoporous gold (NPG) thin membranes and a slight further decoration of Au clusters on top, the resulted core-shell structured NPG-Pd-Au electrocatalyst can demonstrate Pd intrinsic and mass activities of 8.62 mA·cm^-2 and 27.25 A·mg^-1 respectively at the peak potential around 0.33 V versus saturated calomel electrode toward FAOR, which are far better than those of commercial Pd/C catalysts (1.09 mA·cm^-2 and 0.32 A·mg^-1) tested under the same conditions. Moreover, the membrane electrode assemblies based on these low precious metal loading electrodes can achieve an anode Pd power efficiency over 10 W·mg^-1 in a direct formic acid fuel cell, which is two orders of magnitude higher than that of the commercial Pd/C. These results provide new inspirations for the development of revolutionary electrodes for energy technologies in a rational manner.