Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions,b ut still remains arduous.Herein, we demonstrate anovel and general hydrogel-freezed rying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt 3 M( M= Mn, Cr,F e, Co, etc.) intermetallic NPs (Pt 3 M/rGO-HF) with ultrasmall particle size( about 3nm) and dramatic monodispersity.T he formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while af reeze-drying can retain the hydrogel derived threedimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt 3 Mi ntermetallic NPs ( % 3nm) due to confinement effect of 3D porous structure. Such Pt 3 Mi ntermetallic NPs exhibit the smallest particle size among the reported ordered Pt-based intermetallic catalysts.A detailed study of the synthesis of ordered intermetallic Pt 3 Mn/ rGO catalyst is provided as an example of ag enerally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt-based intermetallic catalysts,w hichc an pave aw ay for the commercialization of fuel cell technologies.The need for the practical application of fuel cells has motivated the search of new electrocatalysts with enhanced activity and durability beyond the traditionally employed carbon-supported Pt and Pt-M alloys (M = transition metal). Intermetallic phases,featuring atomically ordered structures, have attracted increasing research attention over the last decade because of their exceptional electronic and structural properties. [1] In contrast to disordered Pt À Ma lloys (solid solution), ordered PtÀMintermetallic compounds have welldefined stoichiometries and provide much better control of the local geometry of metal atoms,r esulting in uniform distribution of active sites on the same surface plane.M ore importantly,t he stronger lattice strain of Pt on intermetallic surfaces can provoke as hift of the d-band center and the change of electronic structure of the surface Pt. This change in electronic structure endows PtÀMintermetallic catalysts with better activity and structural/chemical stability.T od ate, numerous studies have been conducted to investigate PtÀM intermetallic electrocatalysts (M = Fe, [2]

Developing advanced electrocatalysts toward the sluggish oxygen reduction reaction (ORR) kinetics is critical to fuel cells but still an enormous challenge at present. Here, we demonstrate a highly active and durable Pt-based ternary catalyst, ordered Pt3Co0.6Ti0.4 intermetallic nanoparticles (∼3 nm) supported on ZIF-8-derived mesoporous carbon (Pt3Co0.6Ti0.4/DMC). The Pt3Co0.6Ti0.4/DMC catalyst exhibits faster ORR kinetics compared to Pt3Co/DMC and commercial Pt/C with minimal activity loss (20.1%) and only 5 mV decay in half-wave potential after 20,000 potential cycles. More importantly, its improved performances have also been proven in the H2/air PEM single cell test. The theoretical calculations reveal that the substitution of Ti for Co induces a strengthened ligand effect and optimizes the surface electronic structure of Pt3Co0.6Ti0.4, resulting in the significantly enhanced ORR activity. This work provides a reliable and promising approach for the development of efficient and robust Pt-based ternary intermetallic electrocatalysts for practical fuel cell applications.

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...