Ga‐Doped Intermetallic Pd3Pb Nanocubes as a Highly Efficient and Durable Oxygen Reduction Reaction Electrocatalyst

Abstract

Pd‐based nanocrystals are a promising candidate as non‐Pt electrocatalysts for oxygen reduction reaction (ORR), but their performance still has large room to be improved. Here, we have successfully synthesized Ga‐doped Pd3Pb nanocubes with different amounts of Ga by a simple one‐pot approach. When evaluated as electrocatalysts for ORR, the Ga‐doped Pd3Pb nanocubes exhibited substantially enhanced catalytic properties in an alkaline media relative to the Pd3Pb nanocubes and commercial Pt/C. Interestingly, the Ga‐doped Pd3Pb nanocubes showed a volcano‐like relationship in ORR activity as a function of the amount of Ga with the 1.76 % Ga‐doped Pd3Pb nanocubes (Pd3Pb/Ga‐2 NC) being the best ORR electrocatalysts. Specifically, the Pd3Pb/Ga‐2 NC/C exhibited the highest specific (7.57 mA cm−2) and mass activities (0.91 mA μgPd−1), which were 18.0 and 4.3 times higher than those of the commercial Pt/C. In addition, such Pd3Pb/Ga‐2 NC/C displayed the higher durability with an increase of 14.2 % in mass activity after 20000 cycles relative to commercial Pt/C (74.9 % loss). This enhancement in both activity and durability can be attributed to the strong hybridization interactions and the formation of Pd shells on the surface by leaching of Pb.

Microwave Heating of Nanocrystals for Rapid, Low-Aggregation Intermetallic Phase Transformations

“…Using lower power levels or treatment times does not result in phase transformations, as shown by S 2 = 0. We note that, while harmful to the ORR activity, copper doping plays a key role in lowering the energy barrier for phase transformation due to melting point depression: ,,, in the absence of doping, no intermetallic conversion was observed ( S 2 = 0).…”

“…Intermetallic nanocrystals (NCs) are one of the most studied classes of materials for electrocatalysis − due to their high electrochemical stability − at lower precious metal loadings. ,,,− Pt–Co intermetallic face-centered-tetragonal (fct) phase (L1 0 ) NCs have been demonstrated as viable electrocatalysts for the oxygen reduction reaction (ORR). ,− The ability to perform the ORR with high electrochemical stability while decreasing the Pt loading is of key importance for proton exchange membrane fuel cells (PEMFCs), ,,− with the capability of providing a source of clean energy able to compete with fossil fuels . To make PEMFCs economically viable, there is a need to optimize the activity of the catalyst per unit Pt, , also known as the mass activity.…”

“…We use near-monodisperse Cu-doped PtCo 2 NCs in the intermetallic L1 0 phase as a model system. Copper-doping is known to reduce the barrier associated with the phase transformation. ,, The L1 0 phase is desirable because of simultaneously higher electrochemical stability and lower cobalt leaching during catalysis than the random alloy (A1) phase. − ,− ,,,, Typically, as-synthesized A1 face-centered-cubic (fcc) phase NCs are transformed into intermetallic L1 0 NCs by a thermal treatment that involves temperatures exceeding 400 °C over several hours. ,,,,, During this process, NC aggregation, or sintering, occurs, leading to a decrease in the electrochemically active surface area (ECSA) and resulting in a decrease in mass activity for the ORR. ,,, Several literature reports have attempted to prevent NCs from aggregating during the thermal treatment by anchoring the NCs to the substrate, ,, or by synthesizing the NCs directly in the intermetallic phase. ,,− Other methods have demonstrated a monodisperse dispersion of intermetallic NCs; however, these require a specialized technique such as Joule heating or electrochemical dealloying. ,− So far, no method has shown a complete phase transformation with minimized aggregation.…”

“…Copper-doping is known to reduce the barrier associated with the phase transformation. 9,23,24 The L1 0 phase is desirable because of simultaneously higher electrochemical stability and lower cobalt leaching during catalysis than the random alloy (A1) phase. [1][2][3][6][7][8]13,15,19,25 Typically, as-synthesized A1 face-centered-cubic (fcc) phase NCs are transformed into intermetallic L1 0 NCs by a thermal treatment that involves temperatures exceeding 400 °C over several hours.…”

Novel GaPtMnP Alloy Based Anodic Electrocatalyst with Excellent Catalytic Features for Direct Ethanol Fuel Cells

“…The increased lattice spacing in GaPtMnP compared to the standard crystal lattice spacing of 0.226 nm for Pt (111) can be attributed to the co-doping/addition of Ga, Mn, and P atoms into the Pt lattice structure, thus confirming alloy formation. [57,58] The selected area electron diffraction (SAED) pattern (Figure 3F) revealed the polycrystalline nature of GaPtMnP. [21] The elemental mapping (Figure 3G-L) of the GaPtMnP/N-MWCNT nanocomposite catalyst confirmed the presence and distribution of Ga, Pt, Mn, and P along with that of O and N. In addition, the HAADF-STEM image and EDS mapping of GaPtP/N-MWCNT (Figure S5G,J, Supporting Information) confirmed the robust anchoring of GaPtP alloy nanoparticles on N-MWCNT.…”