Dendritic defect-rich palladium–copper–cobalt nanoalloys as robust multifunctional non-platinum electrocatalysts for fuel cells

Recently, the development of high-performance non-platinum electrocatalysts for fuel cell applications has been gaining attention. Palladium-based nanoalloys are considered as promising candidates to substitute platinum catalysts for cathodic and anodic reactions in fuel cells. Here, we develop a facile route to synthesize dendritic palladium–copper–cobalt trimetallic nanoalloys as robust multifunctional electrocatalysts for oxygen reduction and formic acid oxidation. To the best of our knowledge, the mass activities of the dendritic Pd59Cu30Co11 nanoalloy toward oxygen reduction and formic acid oxidation are higher than those previously reported for non-platinum metal nanocatalysts. The Pd59Cu30Co11 nanoalloys also exhibit superior durability for oxygen reduction and formic acid oxidation as well as good antimethanol/ethanol interference ability compared to a commercial platinum/carbon catalyst. The high performance of the dendritic Pd59Cu30Co11 nanoalloys is attributed to a combination of effects, including defects, a synergistic effect, change of d-band center of palladium, and surface strain.

Electrochemical experiment. All of the electrochemical measurements were performed in a conventional three-electrode cell using a CHI 760e electrochemical analyzer (CH Instruments, Inc., Shanghai). A Ag/AgCl electrode and platinum plate were used as reference and counter electrodes, respectively. The FAO working electrode is a glassy carbon (GC, d=4 mm) electrode embedded into a Teflon holder. Before the electrochemical test, we use alumina powder of size 1.5, 1.0 and 0.05 μm to polish the GC electrode, and use ultrapure water clean it in an ultrasonic bath. The suspension of catalysts was spread on the GC electrode. As soon as the electrode was dried under infrared lamp, 4 μL Nafion diluents (1 wt % Nafion® solution) was coated onto the electrode surface.
The cyclic voltammograms (CVs) were obtained in N 2 -saturated 0.1 M HClO 4 solution, and the potential was scanned from-0.25 to 0.9 V (Ag/AgCl) at a scan rate 50 mV s -1 . The scan was repeated several times to ensure that a stable cyclic voltammetry (CV) was obtained.
The electrochemically active surface area (ECSA)tests was estimated by CO stripping test: All working electrodes consisted of catalysts were carried out by firstly in the a CO-saturated 0.1 M HClO 4 solution electrolytic cell, and let the catalyst adsorb CO at 0.20 V for 300 seconds. Then transfered the working electrodes into N 2 -saturated 0.1 M HClO 4 solution electrolytic cell to test from 0.0 to 1.1 V (Ag/AgCl) at a scan rate of 50 mV s -1 . The ECSA was calculated from the charge involved in the CO adsorption processes using the following equation: where Q (mC) is the charge for the CO adsorption. 0.42 (mC/cm 2 ) is the electrical charge associated with full monolayer adsorption of CO on Pd. The average values and related errors, for the ECSA, specific activity and mass activity, were obtained from the results based on the measurement of more than 5 electrodes made of each catalyst.
Characterizations. Transmission electron microscope (TEM) was characterized on a H itachi H-7700 at 100KV. A Tecnai G2 F20 S-Twin high-resolution transmission electr on microscope at 200KV (HRTEM) was used to characterize the sample. A high reso lution aberration corrected transmission electron microscope JEOL-ARM200F, operated at 200kV, was used to perform high-angle annular-dark-field (HAADF) and annular-b right-field (ABF)-STEM and energy-dispersive X-ray spectroscopy (EDS) mapping. X-r ay diffraction (XRD) patterns of the samples were recorded on a Bruker D8 Advance diffractometer with CuK a radiation (l=1.5418Å) with graphite monochromator (40 KV, 40 mA). X-ray photoelectron spectroscopy (XPS) measurements were performed usin g a PHI Quantum 2000 Scanning ESCA Microprobe (Physical Electronics, USA), usin g Al KαX-ray radiation (1486.6 eV) for excitation. Binding energies were corrected fr om charge effects by reference to the C1s peak of carbon at 284.8 eV. The inductive ly coupled plasma optical emission spectrometry (ICP-OES) analysis of samples was p erformed on IRIS Intrepid II XSP (ThermoFisher). X-ray photoelectron spectroscopy o n PHI Quantera SXM.
The X-ray Absorption Fine Structure (XAFS). The X-ray absorption find structure spectra data (Pd K-edge) were obtained at BL14W1 station in Shanghai Synchrotron Radiation Facility (SSRF, operated at 3.5 GeV with a maximum current of 250 mA). The data were obtained at room temperature (Pd K-edge in transmission mode). Graphite powders were used as a binder to pelletize samples into disks with a diameter of 13 mm and a thickness of 1mm.

Supplementary Figures
Supplementary Figure 1