Ordered and Isolated Pd Sites Endow Antiperovskite‐Type PdFe₃N with High CO‐Tolerance for Formic Acid Electrooxidation

Abstract

It has been well accepted that there are two parallel pathways for FAOR on the widely studied Pt and Pd electrodes. [3][4][5][6] Pd has long been regarded as the most promising anode electrocatalyst because it prefers to undergo the direct pathway. [7][8][9][10] Unfortunately, Pd suffers from severe activity loss over hours under certain polarization conditions. It is commonly agreed that the deactivation of the Pd electrode originates chiefly from an accumulation of adsorbed CO (CO*) and "CO*-like" species on surfaces. [11,12] However, the relationship between the deactivation behavior and adsorbed intermediates is still ambiguous and lacks an in-depth understanding.To tackle the issues mentioned above, tremendous endeavors, both experimental and theoretical, have been carried out to gain insights into the deactivation mechanism and rationally design highly efficient, durable, and cost-effective Pd-based electrocatalysts. [13][14][15] Early presumption considered adsorbed carboxyl (COOH*) [16] as the active intermediate but lacks spectral evidence, while the adsorbed formate (HCOO*) is successfully observed by attenuated total reflection surface-enhanced infrared absorption spectroscopy, [17] but its role is controversial. [18][19][20][21][22][23] Mavrikakis proposed that both COOH* and HCOO* are active intermediates but compete with each other, while the former is a precursor to CO. [24] This assumption is verified by the PdH 0.706 catalyst, which tends to undergo HCOO* pathway, leading to lower coverage of CO* and thus higher FAOR activity and stability than Pd. [25] More recently, Koper et al. discovered that high HCOO* coverage on Pd ML Pt (111) single crystal electrode could effectively prevent CO poisoning because of the blocked ensemble site for required CO formation and the highly unfavorable CO binding energy. [26] This result implies that an ideal catalyst for FAOR should have high formate binding energy that improves HCOO* coverage. It is notable that the formate adsorption behavior is closely related to the work function of metal, which is usually optimized by an alloying strategy. [27,28] In particular, intrinsically isolated single atomic sites on alloy surfaces have been proven to possess superior CO tolerance because continuous active sites are segregated by host metal. [29][30][31][32][33] However, for the widely studied Pd-based alloys (solid solution), it is a The fundamental understanding and precise control of catalytic sites are challenging yet essential to explore advanced electrocatalysts for the formic acid oxidation reaction (FAOR). Herein, this work demonstrates a new and promising catalyst prototype of antiperovskite-type PdFe 3 N which possesses ordered and isolated Pd sites. The as-synthesized PdFe 3 N/N-rGO exhibits significant enhancement in catalytic activity, robust stability, and Fe antidissolution properties when compared with PdFe 3 /rGO and Pd/C. Density functional theory (DFT) calculations reveal that isolated and ordered Pd sites are beneficial for high formate coverage an...

Terbium-induced cobalt valence-band narrowing boosts electrocatalytic oxygen reduction

“…The porous structure with a high specific surface area can shorten the electron/ion transfer path and offer a convenient channel for mass diffusion in electrocatalysis. 44–46 The good dispersion of particles on NC nanosheets was further confirmed by transmission electron microscopy (TEM) images (Fig. 2(A) and (B)).…”

“…The porous structure with a high specific surface area can shorten the electron/ion transfer path and offer a convenient channel for mass diffusion in electrocatalysis. [44][45][46] The good dispersion of particles on NC nanosheets was further confirmed by transmission electron microscopy (TEM) images (Fig. 2 The Co@Tb 2 O 3 /NC delivers an onset potential (E onset ) and halfwave potential (E 1/2 ) of about 1.02 V RHE and 0.85 V RHE respectively, which outperforms Co/NC (E onset = 0.94 V RHE , E 1/2 = 0.79 V RHE ) and Tb 2 O 3 /NC (E onset = 0.86 V RHE , E 1/2 = 0.71 V RHE ).…”

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

“…XRD patterns of nanocrystals with different synthetic conditions, most commonly, different annealing temperatures, are succinct and powerful when illustrating the phase-transformation process from alloy to intermetallics so as to extrude the key condition/temperature, therefore, are most universally applied as ordered-phase proof at first glance. ,,,, Furthermore, information about extra lattice strain and average grain size can also be obtained from XRD patterns by the relevant facet peak shifting and half-peak width. The former may paralleled with Rietveld refining, contribute to provide fuller structural sketch of heteroatoms or vacancies-doped/substituted intermetallics about their unit cell parameters, atomic site and occupancy, microstrain, etc., yet the latter may companied by size distribution analysis and help to evaluate the influence of size effect. , …”

“…When facing unexplored novel intermetallic phases, Rietveld refining of XRD pattern serves as an ultimate tool to help researchers identify the lattice structure. Taking PdFe 3 N as an example, a new class of antiperovskite-type intermetallic compound was first successfully synthesized and applied to electrocatalysis . XRD Rietveld refining was used to deal with the extra superlattice peaks and unraveled that extra N atoms occupy the body-central position.…”

“…Further going, PtSnBi trimetallic intermetallics also has been reported as ideal FAOR catalyst due to optimal synergism between three tailored elements. , Bi determines the preferable dehydrogenation pathway for complete oxidation of FA, while Sn boosts the adsorption of hydroxyl so as to reduce the energy barrier of RDS. Particularly, hybrid ternary intermetallics with nonmetal N element, and unique antiperovskite structure was also developed . The as-studied PdFe 3 N intermetallics possesses isolated and ordered Pd sites with high formate coverage and thus suppressive CO poisoning.…”