BCC-Phased PdCu Alloy as a Highly Active Electrocatalyst for Hydrogen Oxidation in Alkaline Electrolytes

Abstract

Anion-exchange membrane fuel cells hold promise to greatly reduce cost by employing nonprecious metal cathode catalysts. More efficient anode catalysts are needed, however, to improve the sluggish hydrogen oxidation reaction in alkaline electrolytes. We report that BCC-phased PdCu alloy nanoparticles, synthesized via a wet-chemistry method with a critical thermal treatment, exhibit up to 20-fold HOR improvement in both mass and specific activities, compared with the FCC-phased PdCu counterparts. HOR activity of the BCC-phased PdCu is 4 times or 2 times that of Pd/C or Pt/C, respectively, in the same alkaline electrolyte. In situ HE-XRD measurements reveal that the transformation of PdCu crystalline structure favors, at low annealing temperature (<300 °C), the formation of FCC structure. At higher annealing temperatures (300−500 °C), a BCC structure dominates the PdCu NPs. Density functional theory (DFT) computations unravel a similar H binding strength and a much stronger OH binding of the PdCu BCC surface (cf. FCC surface), both of which are simultaneously close to those of Pt surfaces. The synergistic optimization of both H and OH binding strengths is responsible for the enhancement of HOR activity on BCC-phased PdCu, which could serve as an efficient anode catalyst for anion-exchange membrane fuel cells. This work might open a new route to develop efficient HOR catalysts from the perspective of crystalline structure transformation.

Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel‐Based Metal–Organic Framework

“…In contrast, NiO (111) shows a smaller hydroxide binding energy of 0.54 eV while Ni (111) even has a slightly negative value of −0.07 eV. It is generally believed that electrocatalysts with hydrogen and hydroxide binding energies similar to Pt would exhibit excellent HOR performance, which is indeed the case for our Ni/NiO sample. Overall, interfacing Ni and NiO optimizes both electronic (hydrogen binding energy) and oxophilic (hydroxide binding) effects and synergistically results in excellent HOR (and HER) performance under alkaline conditions.…”

“…Further to hydrogen adsorption, the interaction of hydroxide anions with the catalyst surface arguably plays an equally important role in the overall HOR process . Figure b presents the optimal site on Ni/NiO towards hydroxide adsorption with a binding energy of 0.72 eV (Figure d), very close to the binding energy on Pt (111) (0.87 eV).…”

“…demonstrated that optimized adsorption of hydroxyl species (OH*) could also promote the overall hydrogen oxidation rate in alkaline electrolytes . Indeed, a number of electrocatalyst systems consisting of two constituents (metals and/or metal oxides) have been reported with enhanced HOR performance with the secondary components showing optimal OH* binding, including Pt‐CeO 2 , Rh‐Rh 2 O 3 , PdNi, and PdCu . Nevertheless, these electrocatalyst systems typically contain platinum group metals (PGMs) and are thus not cost‐effective.…”

“…To shed more light on the possible active sites of Ni/NiO/C‐700 and the origin of its high intrinsic activity towards H 2 oxidation, density functional theory (DFT) calculations were also conducted. Since Pt is the state‐of‐the‐art HOR electrocatalyst, the hydrogen binding energy on Pt (111) was computed (−0.40 eV) and served as a benchmark for comparison (Supporting Information, Figure S31) . It is apparent that both NiO (−1.27 eV) and Ni (−0.54 eV) possess much stronger hydrogen binding energy than Pt (Figure c), whereas the Ni/NiO interface model exhibits an even smaller value (−0.20 eV).…”

Bimetallic nickel-molybdenum/tungsten nanoalloys for high-efficiency hydrogen oxidation catalysis in alkaline electrolytes

“…Numerous PGMs, such as Pt, palladium (Pd), iridium (Ir), ruthenium (Ru), and rhodium (Rh,) have been studied for HOR in alkaline electrolytes 10,12 , among which Pt and Ir are particularly active and stable. Moreover, alloying PGMs with other metals can enable performance enhancements resulting from the modified surface structures; typical examples include PtNi 13 , PtRu 14 , Pt-coated Cu 15 , body-centered cubic PdCu 9 , and others [16][17][18][19][20] . In the quest to understand why the HOR reactivity in alkaline media is significantly slower than that in acid on PGMs, there has been extensive debate over whether such sluggish HOR kinetics in alkali is determined by hydrogen binding energy (HBE) or OH binding energy (OHBE)/ oxophilicity 8,10,11,13,[21][22][23][24][25][26][27] .…”