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Direct formic acid fuel cells have attracted significant attention due to their low fuel crossover, high safety, and high theoretical power density among all proton‐exchange membrane fuel cells. Numerous efforts have been dedicated to studying formic acid oxidation, particularly in the fabrication of high‐performance electrocatalysts with economical utilization of Pt metal. In this work, we report a synthetic strategy to create PtAg dots supported on plate‐like Au nanoparticles and explore their applications in electrocatalytic formic acid oxidation. The highly dispersed nature of the catalytic Pt centers and the successful construction of PtAg−Au trimetallic interfaces makes the current nanostructure an ideal system to allow for a synergetic effect between Pt, Au, and Ag, leading to improved electrocatalysis. Compared with commercial Pt/C, our PtAg‐on‐Au heterogenous nanoplates exhibit superior mass activity, along with enhanced reaction kinetics and long‐term durability for FAOR in an acidic medium. Density functional theory (DFT) simulation results indicate that AgPtAu(111) exhibits a relatively high activity for HCOOH oxidation into CO2 among the various Au‐based catalysts. This work provides a viable strategy for constructing Pt‐based electrocatalysts with controlled Pt ensembles, offering insights into the development of fuel cell catalysts that make highly efficient use of costly noble metals. [ABSTRACT FROM AUTHOR]

The strong ligand effect in B‐doped Pd‐based (PdB) catalysts renders them a promising anode for constructing formic acid fuel cells (FAFCs) exhibiting high power density and outstanding stability. However, the enhancement of the oxidation barrier is unavoidable in this alloy system owing to the electron transfer (ET) from B to Pd. In this study, a hydrogen doping strategy is employed to open charge freedom in PdB compounds and boost their formic acid oxidation reaction (FAOR) activity by suppressing the ET process. The resulting hydrogen‐doped PdB (PdBH) exhibits an ultrahigh mass activity of up to 1.2A mg−1Pd, which is 3.23 times that of the PdB catalyst and 9.55 times that of Pd black. Detailed experimental and theoretical studies show that the interstitial hydrogen leads to enhanced orbital hybridization and reduced electron density around Pd. This optimized ligand effect weakens the carbon monoxide adsorption and increases the direct pathway preference of PdBH, resulting in its outstanding catalytic activity for the FAOR. The development of this high‐performance hydrogen‐doped PdB catalyst is an important step toward the construction of advanced light element co‐doped metal catalysts. [ABSTRACT FROM AUTHOR]

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal‐based catalysts. Herein, high‐entropy intermetallics i‐(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple‐scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well‐enhanced mass activity/durability than that of ternary i‐Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high‐entropy alloys. [ABSTRACT FROM AUTHOR]

Abstract The strong ligand effect in B‐doped Pd‐based (PdB) catalysts renders them a promising anode for constructing formic acid fuel cells (FAFCs) exhibiting high power density and outstanding stability. However, the enhancement of the oxidation barrier is unavoidable in this alloy system owing to the electron transfer (ET) from B to Pd. In this study, a hydrogen doping strategy is employed to open charge freedom in PdB compounds and boost their formic acid oxidation reaction (FAOR) activity by suppressing the ET process. The resulting hydrogen‐doped PdB (PdBH) exhibits an ultrahigh mass activity of up to 1.2A mg−1Pd, which is 3.23 times that of the PdB catalyst and 9.55 times that of Pd black. Detailed experimental and theoretical studies show that the interstitial hydrogen leads to enhanced orbital hybridization and reduced electron density around Pd. This optimized ligand effect weakens the carbon monoxide adsorption and increases the direct pathway preference of PdBH, resulting in its outstanding catalytic activity for the FAOR. The development of this high‐performance hydrogen‐doped PdB catalyst is an important step toward the construction of advanced light element co‐doped metal catalysts.

Numerous studies have reported the development of Pd-based catalyst for the anode direct formic acid fuel cell (DFAFC) that improves the electrocatalytic activities. We have now developed a carbon nanofiber embedded with carbon black (Vulcan) and molybdenum sulfide (MoS 2) nanoparticles as the Pd support for the FAOR catalyst. The MoS 2 -Vulcan embedded carbon nanofiber (MoS-VECNF) was first prepared by electrospinning and heat treatment. The MoS-VECNF was prepared with different weight ratios of MoS 2 to polyacrylonitrile (PAN). The prepared support was then loaded with 20 wt% Pd nanoparticles by the polyol method. The Pd/MoS-VECNF catalyst demonstrated a better FAOR activity and stability as compared to the Pd/VECNF catalyst with 0.10 as the optimum weight ratio. The achieved peak current density was 1.46 times higher than that of the Pd/VECNF catalyst. The presence of MoS 2 nanoparticles in the carbon support produced a strong metal-support interaction which improved the FAOR activity and stability of the catalyst. Therefore, the Pd/MoS-VECNF catalyst is suggested to be promising for DFAFC applications. • Molybdenum-containing carbon nanofiber supported Pd catalyst was synthesized. • Pd/MoS-VECNF catalysts were tested for formic acid oxidation. • Formic acid oxidation activity is improved by the addition of molybdenum. • Superior stability is achieved by the molybdenum-containing catalyst. • Pd/MoS-VECNF catalyst is promising for direct formic acid fuel cells application. [ABSTRACT FROM AUTHOR]

Spreading the formic acid (HCOOH) fuel cells demands a better anode electrocatalyst for the oxidation of formic acid. The catalytic efficiency of platinum (Pt)– the only choice of practicability, is mainly limited by its intrinsic affinity to CO, thus desiring a proper release. Herein, theoretical calculations are first leveraged to find that the introduction of iridium (Ir) can facilitate HCOOH oxidation with robust CO tolerance through a dehydrogenation pathway. Then, this strategy experimentally by designing a new trimetallic catalyst of 2D porous PtIrBi nanoplates (p‐PtIrBi NPs) is implemented. The optimized p‐PtIrBi NPs/C exhibits a very high mass activity of 8.2 A mg−1pt and a high retention rate of 55.9% after the durability test, which is among the best formic acid oxidation catalysts reported to date, much higher than those of PtIrBi NPs/C, PtBi NPs/C, and Pt/C. The CO‐stripping and in situ Fourier transform infrared (FTIR) experiments collectively evidence that two types of due site, i.e., "Pt‐Bi" and "Ir‐Bi", endow the catalyst with suppressed CO‐poisoning property to achieve super‐high activity and stability for formic acid oxidation reaction. [ABSTRACT FROM AUTHOR]

Although palladium (Pd) based materials are considered the best catalyst for formic acid oxidation reaction (FAOR), they are still confronted with a lot of barriers, such as the growth/sintering of Pd nanoparticles (NPs) and the accumulation of adsorbed poisoning intermediates. Herein, tin dioxide (SnO 2) decorated carbon black was utilized as the catalyst carrier to synthesize Pd/SnO 2 /C for FAOR. The introduction of SnO 2 significantly reduced the particle size of Pd NPs and forming the Pd–O–Sn structure. Compared with Pd/C, Pd/SnO 2 /C owned higher concentration of O ads and less adsorption amount of poisoning intermediates. The oxygen atoms adsorbed on Pd surface were rapidly transferred to SnO 2 due to the spillover effect. The FAOR reaction kinetic results showed that the introduction of SnO 2 accelerated the diffusion rate of formic acid on the electrode surface. Pd/SnO 2 /C exhibited high specific activity (5.97 mA cm−2), excellent durability, and high anti-CO poisoning ability toward FAOR due to the introduction of SnO 2. •The defects and holes of SnO 2 anchor Pd and promote the dispersion of Pd NPs. •Pd–O–Sn is formed and promotes generating oxygen-containing substances on SnO 2. •The spillover effect of Pd enhances the formation of O ads on Pd/SnO 2 /C. •In-situ ATR-IR confirms that less CO ads (i.e., CO M , CO B) are adsorbed on Pd/SnO 2 /C. •The introduction of SnO 2 kinetically accelerates the mass transfer of formic acid. [ABSTRACT FROM AUTHOR]

Herein, an electrocatalyst with Pd2Ni1 nanoclusters, supporting multiwalled carbon nanotubes (MWCNTs) (referred to Pd2Ni1/CNTs), was fabricated with deep eutectic solvents (DES), which simultaneously served as reducing agent, dispersant, and solvent. The mass activity of the catalyst for formic acid oxidation reaction (FAOR) was increased nearly four times compared to a Pd/C catalyst. The excellent catalytic activity of Pd2Ni1/CNTs was ascribed to the special nanocluster structure and appropriate Ni doping, which changed the electron configuration of Pd to reduce the d-band and to produce a Pd–Ni bond as a new active sites. These newly added Ni sites obtained more OH− to release more effective active sites by interacting with the intermediate produced in the first step of FAOR. Hence, this study provides a new method for preparing a Pd–Ni catalyst with high catalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanophase-separated ternary PdAgCu nanotubes are synthesized by a facile method. • The surface morphology of PdAgCu nanotubes could be tuned from smooth to rough. • The mass activity of S-PdAgCu NTs for FAOR can reach up to 4307 mA mg Pd -1. • The enhanced performance is derived from the synergistic effect and dense surface. Herein, a facile strategy for the preparation of PdAgCu ternary nanotubes (NTs) is introduced by using Cu nanowires (NWs) as sacrificial templates along with an acid-leaching treatment. Since the phase separation between Ag and Cu, the obtained PdAgCu NTs is made up of various nanosphases including pure Ag, Cu, bimetallic PdCu and PdAg nanoalloys, instead of PdAgCu trimetallic nanoalloys. By adjusting the types of solvents during synthesis, the surface morphology of PdAgCu NTs can be tuned from smooth (S-PdAgCu NTs) to rough (R-PdAgCu NTs). Both S-PdAgCu NTs and R-PdAgCu NTs exhibit excellent electrocatalytic performances for formic acid oxidation reaction (FAOR). Remarkably, the mass activity of S-PdAgCu NTs for FAOR can reach up to 4307 mA mg Pd -1 at peak potential, which is 8.5 times higher than that of commercial Pd (506 mA mg Pd -1). The impressively enhanced activity should be ascribed to the synergistic effect of Pd with Cu or Ag and the multi-phase interface engineering, which is resulting from the tight position relationships among different monometallic or bimetallic alloy nanophases. [ABSTRACT FROM AUTHOR]

Abstract The development of an efficient catalyst for formic acid electrocatalytic oxidation reaction (FAEOR) is of great significance to accelerate the commercial application of direct formic acid fuel cells (DFAFC). Herein, palladium phosphide (PdxPy) porous nanotubes (PNTs) with different phosphide content (i.e., Pd3P and Pd5P2) are prepared by combining the self‐template reduction method of dimethylglyoxime‐Pd(II) complex nanorods and succedent phosphating treatment. During the reduction process, the self‐removal of the template and the continual inside–outside Ostwald ripening phenomenon are responsible for the generation of the one‐dimensional hollow and porous architecture. On the basis of the unique synthetic procedure and structural advantages, Pd3P PNTs with optimized phosphide content show outstanding electroactivity and stability for FAEOR. Importantly, the strong electronic effect between Pd and P promotes the direct pathway of FAEOR and inhibits the occurrence of the formic acid decomposition reaction, which effectively enhances the FAEOR electroactivity of Pd3P PNTs. In view of the facial synthesis, excellent electroactivity, high stability, and unordinary selectivity, Pd3P PNTs have the potential to be an efficient anode electrocatalyst for DFAFC.

The electrochemical formic acid oxidation reaction (FAOR) has attracted great attention due to its high volumetric energy density and high theoretical efficiency for future portable electronic applications, for which the development of highly efficient and low-cost electrocatalysts is of great significance. In this work, taking single-atom catalysts (SACs) supported on graphitic carbon nitrides (g-CN) as potential catalysts, their catalytic performance for the FAOR was systemically explored by means of density functional theory computations. Our results revealed that the strong hybridization with the unpaired lone electrons of N atoms in the g-CN substrate ensured the high stability of these anchored SACs and endowed them with excellent electrical conductivity. Based on the computed free energy changes of all possible elementary steps, we predicted that a highly efficient FAOR could be achieved on Ru/g-CN with a low limiting potential of −0.15 V along a direct pathway of HCOOH(aq) → HCOOH* → HCOO* → CO2* → CO2(g), in which the formation of HCOO* was identified as the potential-determining step, while the rate-determining step was located at the CO2* formation, with a moderate kinetic barrier of 0.89 eV. Remarkably, the moderate d-band center and polarized charge of the Ru active site caused the Ru/g-CN catalyst to exhibit an optimal binding strength with various reaction intermediates, explaining well its superior FAOR catalytic performance. Hence, the single Ru atom anchored on g-CN could be utilized as a promising SAC for the FAOR, which opens a new avenue to further develop novel catalysts for a sustainable FAOR in formic-acid-based fuel cells. [ABSTRACT FROM AUTHOR]

Nearly theoretical 100% atomic utilization (supposing each atom could serve as independent sites to play a role in catalyz) of single‐atom catalysts (SACs) makes it highly promising for various applications. However, for most SACs, single‐atom sites are trapped in a solid carbon matrix, which makes the inner parts hardly available for reaction. Herein, a hollow N‐doped carbon confined single‐atom Rh (Rh‐SACs/HNCR) is developed via a coordination‐template method. Both aberration‐corrected scanning transmission electron microscopy and energy dispersive X‐ray spectroscopy mapping confirm the uniform distribution of Rh single atoms. Owning to the unique hollow structure and effective carbon confinement, excessive conversion from pyridinic/pyrrolic N to graphic N is hindered. As a proof of concept, Rh‐SACs/HNCR exhibits superior activity, stability, selectivity, and anti‐poisoning capability in formic acid oxidation reaction compared with the counterpart Rh/C, Pd/C, and Pt/C catalysts. This work provides a powerful strategy for synthesizing hollow carbon confined single‐atom catalysts apply in various energy‐related systems. [ABSTRACT FROM AUTHOR]

Abstract Nearly theoretical 100% atomic utilization (supposing each atom could serve as independent sites to play a role in catalyz) of single‐atom catalysts (SACs) makes it highly promising for various applications. However, for most SACs, single‐atom sites are trapped in a solid carbon matrix, which makes the inner parts hardly available for reaction. Herein, a hollow N‐doped carbon confined single‐atom Rh (Rh‐SACs/HNCR) is developed via a coordination‐template method. Both aberration‐corrected scanning transmission electron microscopy and energy dispersive X‐ray spectroscopy mapping confirm the uniform distribution of Rh single atoms. Owning to the unique hollow structure and effective carbon confinement, excessive conversion from pyridinic/pyrrolic N to graphic N is hindered. As a proof of concept, Rh‐SACs/HNCR exhibits superior activity, stability, selectivity, and anti‐poisoning capability in formic acid oxidation reaction compared with the counterpart Rh/C, Pd/C, and Pt/C catalysts. This work provides a powerful strategy for synthesizing hollow carbon confined single‐atom catalysts apply in various energy‐related systems.

Recently, Pt-based catalysts on mixed carbon supporters have been introduced for enhancement of the formic acid oxidation (FAO) reaction. Herein, carbon black (CB) and carbon nanotubes (CNT) were combined as a hybrid CB-CNT carbon support. The Brunauer–Emmett–Teller (BET) surface area of CB-CNT support presented the increased pore size and volume, providing high surface areas for electroactive species diffusion. By cyclic voltammetry (CV), the noble metals (M) including platinum (Pt), palladium (Pd), gold (Au), and ruthenium (Ru) were utilized for catalytic electrodepositing on the CB-CNT support to obtain the catalysts. The M/CB-CNT and PtM/CB-CNT catalysts prepared under the controlled condition were characterized and compared their activities and stabilities. Among the prepared catalysts, the small particle sizes of PtM/CB-CNT, which occurred with high Pt(111) intensities from face-centered cubic (fcc) structure, were confirmed by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Also, the X-ray photoelectron spectroscopy (XPS) indicated the highest peak ratio of metallic Pt from PtPd/CB-CNT that was related to its high catalytic active surfaces. In the monometallic systems, the Pt/CB-CNT and Pd/C-CNT catalysts actively promote the oxidation of formic acid molecules by their unique pathways. Among the prepared catalysts in both mono- and bimetallic systems, PtPd/CB-CNT showed the highest current intensity of 11.48 mA cm−2 at a potential of 0.70 V in FAO reaction for formic acid oxidation. Although Pt/CB-CNT provided the lowest potential at maximum current intensity (ECO = 0.51 V), PtPd/CB-CNT astonishingly presented the highest active surface area (ECSACO = 0.57 cm2) for CO oxidation. The PtPd/CB-CNT catalyst showed the co-existence between Pt and Pd nanoparticles, and the hybrid structure of CB-CNT provided the improved electrochemical results towards FAO reaction. [ABSTRACT FROM AUTHOR]

• Innovative 3D PtRhNiCoFeGaW HEA design maximizes exposure of active sites. • Strain and lattice distortion in PtRhNiCoFeGaW HEA optimize catalytic sites. • PtRhNiCoFeGaW HEA significantly enhances MOR and FAOR efficiency. • Intricate elemental synergy in PtRhNiCoFeGaW HEA reduces CO poisoning risk. Addressing the pivotal challenge of lattice distortion and electronic structure modulation in High-Entropy Alloys (HEAs) for electrochemical catalysis, this investigation presents the synthesis of a novel PtRhNiCoFeGaW HEA in a three-dimensional nanoflower configuration. This design strategically combines enhanced morphological features and a synergistic metallic interaction, propelling the catalytic efficiency forward in methanol and formic acid oxidation reactions (MOR and FAOR). The synthesized HEA nanoflowers exhibit superior mass and specific activities of up to 1.34 mA μg Pt −1 and 4.43 mA cm−2 for MOR, alongside 0.52 mA μg Pt −1 and 1.74 mA cm−2 for FAOR, markedly surpassing those of conventional Pt/C and PtRhNi NFs. This leap in performance is primarily attributed to the intricate elemental synergy within the HEAs, which effectively minimizes CO poisoning (a notorious catalyst deactivator) by improving CO* resistance. Furthermore, the study delineates how the unique nanoflower morphology contributes to exposing a plethora of active sites, thereby maximizing catalytic action. This research not only navigates through the complexities of crafting multi-elemental catalytic systems but also establishes a foundational strategy for developing next-generation HEA-based electrocatalysts, poised to significantly impact future advancements in energy conversion technologies. [ABSTRACT FROM AUTHOR]

The development of an efficient catalyst for formic acid electrocatalytic oxidation reaction (FAEOR) is of great significance to accelerate the commercial application of direct formic acid fuel cells (DFAFC). Herein, palladium phosphide (PdxPy) porous nanotubes (PNTs) with different phosphide content (i.e., Pd3P and Pd5P2) are prepared by combining the self‐template reduction method of dimethylglyoxime‐Pd(II) complex nanorods and succedent phosphating treatment. During the reduction process, the self‐removal of the template and the continual inside–outside Ostwald ripening phenomenon are responsible for the generation of the one‐dimensional hollow and porous architecture. On the basis of the unique synthetic procedure and structural advantages, Pd3P PNTs with optimized phosphide content show outstanding electroactivity and stability for FAEOR. Importantly, the strong electronic effect between Pd and P promotes the direct pathway of FAEOR and inhibits the occurrence of the formic acid decomposition reaction, which effectively enhances the FAEOR electroactivity of Pd3P PNTs. In view of the facial synthesis, excellent electroactivity, high stability, and unordinary selectivity, Pd3P PNTs have the potential to be an efficient anode electrocatalyst for DFAFC. [ABSTRACT FROM AUTHOR]

Electrochemical energy storage and conversion toward sustainable carbon neutrality cycle is of great interest in today's society. In this perspective, we highlight the interconversion between carbon dioxide and formic acid by means of electrocatalytic CO2 reduction reaction (CO2RR) and formic acid oxidation reaction (FAOR) as an effective way to achieve that goal. In line with the distinctive catalytic nature of Pd to reversibly drive both FAOR and CO2RR, we first illustrate the intimate mechanistic relation between these two reversed reactions over Pd surfaces. Next, recent advances in developing Pd-based bifunctional catalysts and relevant optimization strategies are briefly summarized, including geometric structure engineering with preferential facet exposure, construction of crystallographic ordering intermetallic, electronic structure manipulation through metal or metalloid doping to fine tune the binding strength for active and poisoning intermediates. At the end, our viewpoints on the design principles at both microscopic and macroscopic scales are offered toward an efficient CO2 and HCOOH interconversion loop.

Herein, an electrocatalyst with Pd2Ni1 nanoclusters, supporting multiwalled carbon nanotubes (MWCNTs) (referred to Pd2Ni1/CNTs), was fabricated with deep eutectic solvents (DES), which simultaneously served as reducing agent, dispersant, and solvent. The mass activity of the catalyst for formic acid oxidation reaction (FAOR) was increased nearly four times compared to a Pd/C catalyst. The excellent catalytic activity of Pd2Ni1/CNTs was ascribed to the special nanocluster structure and appropriate Ni doping, which changed the electron configuration of Pd to reduce the d-band and to produce a Pd–Ni bond as a new active sites. These newly added Ni sites obtained more OH− to release more effective active sites by interacting with the intermediate produced in the first step of FAOR. Hence, this study provides a new method for preparing a Pd–Ni catalyst with high catalytic performance.

Recently, a primary challenge hindering the commercialization of direct fuel cells is the development of robust nonplatinum electrocatalysts to improve the performance of the oxygen reduction reaction (ORR) and formic acid oxidation reaction (FAOR). In this paper, polyol reduction and high temperature calcination carbonization were used to improve the conductivity of the catalyst by the modification of rare earth Ce. Pd has similar properties to Pt, with one-fifth of the properties of Pt, and the rare earth elements have low electronegativity, making it easy to supply electrons and fill Pd's antibonding orbitals. Rare Earth elements effectively enhance ORR activity by making palladium more metallic. The high-activity, low-cost and high-stability electrocatalytic ORR and FAOR catalysts Pd x Ce/C were designed. After a series of testing methods, the physical properties and electrochemical properties were characterized, and the optimum structure and composition were selected. The stability of the catalyst with the optimal structure and composition was assessed, and it was applied to various composite batteries to verify its capability in practical application. ● Successful synthesis of carbon-supported Pd-Ce nanoparticles with different molar ratios. ● Pd 3 Ce/C-500 exhibits high activity and durability for oxygen reduction reaction. ● Pd 3 Ce/C-300 has better oxidation performance than commercial catalysts for formic acid. ● Pd 3 Ce/C-300 and Pd 3 Ce/C-500 can be well used in Self-assembly fuel cell. [ABSTRACT FROM AUTHOR]

The construction of platinum (Pt) atomic layers is an effective strategy to improve the utilization efficiency of Pt atoms in electrocatalysis, thus is important for reducing the capital costs of a wide range of energy storage and conversion devices. However, the substrates used to grow Pt atomic layers are largely limited to noble metals and their alloys, which is not conducive to reducing catalyst costs. Herein, low-cost chromium nitride (CrN) is utilized as a support for the loading of epitaxial ultrathin Pt atomic layers via a simple thermal ammonolysis method. Owing to the strong anchoring and electronic regulation of Pt atomic layers by CrN, the obtained Pt atomic layers catalyst (containing electron-deficient Pt sites) exhibits excellent activity and endurance for the formic acid oxidation reaction, with a mass activity of 5.17 A mg Pt -1 that is 13.6 times higher than that of commercial Pt/C catalyst. This novel strategy demonstrates that CrN can replace noble metals as a low-cost substrate for constructing Pt atomic layers catalysts., (© 2023 Wiley-VCH GmbH.)

Concurrently optimizing the pathway and electrocatalytic activity for formic acid oxidation reaction (FAOR) is significant but still challenging. Herein, surface and composition engineering strategies are integrated by constructing atomically ordered Rh 0.9 Pt 0.1 Fe ternary intermetallic (O -Rh 0.9 Pt 0.1 Fe). Supported by the in situ infrared spectra, the carbon monoxide (CO*) mediated indirect FAOR pathway on pure Rh is switched into a direct pathway on RhFe intermetallics (O -RhFe) with isolated Rh atoms, leading to a lower overpotential. Further composition engineering by forming O -Rh 0.9 Pt 0.1 Fe contributes to enhanced FAOR activity due to the stabilizing of COOH* intermediate, as indicated by the density functional theory calculations. Besides, O -Rh 0.9 Pt 0.1 Fe shows enhanced FAOR activity during potential cycling tests with fewer structural evolutions, while O -RhFe displays a decay. This study provides new insight into tuning reaction pathways and catalytic activity selectively via tailoring adsorption of different intermediates. [Display omitted] • Constructing a series of Rh-based intermetallics with various phases and compositions. • Probing the reaction intermediates via electrochemical in situ spectroscopy. • Revealing formic acid oxidation reaction mechanism via density function theory calculations. • Guiding the design of highly efficient and durable electrocatalysts for formic acid oxidation reaction. [ABSTRACT FROM AUTHOR]

Trioctylphosphine is firstly introduced in the CO-assisted solvothermal method to synthesize uniform Pd nanotetrahedrons, which are surface-doped with Pt atoms for highly efficient electrocatalytic oxygen reduction and formic acid oxidation. [Display omitted] • TOP is firstly introduced in the CO-assisted Pd shape-controlled synthetic method. • Small-sized, uniform, and highly selective Pd NTs are obtained via this method. • Pd NTs are surface-doped with Pt atoms by the modified Pt2+ galvanic replacement. • Pd/SDPt NTs exhibit highly efficient ORR and FAOR electrocatalytic performance. • The structure-function relations are studied both experimentally and theoretically. Increasing the accessible active sites and especially improving the intrinsic activity are two major effective strategies for enhancing the electrocatalytic activity of nanomaterials. Accordingly, through the trioctylphosphine (TOP)-based CO-assisted solvothermal method and the small-amount Pt2+ galvanic replacement, highly uniform Pd nanotetrahedrons (NTs) with Pt-doped surfaces are synthesized and supported onto carbon black. Comprehensive experimental and theoretical analyses reveal that, owing to the Pt surface-doped (SD) nanostructure, the conformal formation of surface Pt {111} facets, as well as the strain and electronic effects induced by the Pd–Pt alloy structure, Pd/SDPt NTs/C exhibits much better electrocatalytic performance than Pd NTs/C, commercial Pd/C, and Pt/C toward both oxygen reduction and formic acid oxidation reactions, showing greatly improved metal utilization and area/mass-specific activity. This study develops a high-performance bifunctional electrocatalyst, and firstly introduces TOP as the easy-removable surface-energy adjuster for the Pd shape-controlled synthesis, which may be further expanded to other metals and shapes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomic Pt clusters are simply fabricated on Au dendrite for FAOR. • The isolated Pt sites on Au demonstrated high selectivity for direct FAOR pathway. • Extremely high FAOR mass activities are obtained in half cell and single cell test. • The CO chemisorption analysis confirmed the stability of isolated Pt sites after FAOR. The minimization of Pt loadings on Au via facile fabrication methods remains a grand challenge in the development of commercially viable electrodes for direct formic acid fuel cells. Herein, we report a simple electrochemical strategy to prepare atomic Pt clusters on Au dendrites supported by carbon paper (CP) as a gas diffusion electrode. At highly negative deposition potentials, Pt deposition is autonomously quenched by immediate adsorption of discharged proton (H) on Pt surface, while highly roughened Au dendrites lead to resistance–capacitance delay for the transient cathodic current. As a result, the suppressed Pt nucleation and self-terminated Pt growth allows for the formation of isolated Pt sites on Au dendrites. The Pt/Au/CP with an ultra-low Pt loading of 5.0 μg Pt /cm geo 2 demonstrates high selectivity for direct pathway of formic acid oxidation reaction (FAOR), owing to the ensemble effect. A gradual increase of FAOR activity is observed during cycling test and then, the 20 cycled Pt/Au/CP shows remarkable FAOR activity in half-cell test, exceeding state-of-the-art Pt-Au catalysts. Theoretical calculation indicates that the stabilized intermediate on Pt clusters accelerates the direct FAOR pathway. CO chemisorption analysis reveals that the isolated Pt sites remain stable throughout the reaction. Single cell test for direct formic acid fuel cell with 20 cycled Pt/Au/CP anode demonstrate two-order higher Pt mass activity and mass power density, compared with values reported in recent literature. [ABSTRACT FROM AUTHOR]

A newly designed NCCP alloy demonstrates a high electrocatalytic performance for FAOR. Quaternary NCCP alloys is synthesized using the facile one-step wet-chemical reaction. In this reaction, a chemically obtained hierarchical core–shell structure and Pd nanoclusters-NiCo shell-Cu interior evolved due to different immiscibility. The mass activity of NCCP for FAOR is 3.6 folds higher than the benchmark Palladium on Carbon (Pd/C, 10 wt%) catalyst. [Display omitted] • Quaternary NCCP alloys developed using the facile one-step wet-chemical reaction. • NCCP alloys show an intriguing core–shell nanostructure which can increases rate of formic acid oxidation reaction. • NCCP catalyst demonstrates high mass activity for formic acid oxidation reaction. • NCCP exhibits 3.6 folds higher mass activity for FAOR compared to the commercial Pd/C (10 wt%) catalyst. Development of efficient electrocatalyst with a small use of noble metals for formic acid oxidation reaction (FAOR) is the most urgent need in realizing practical direct formic acid fuel cells (DFAFC). Herein, we developed quaternary Ni-Co-Cu-Pd (NCCP) alloys with an intriguing nanostructure, that is, hierarchical core–shell structure, which demonstrates excellent catalytic performance for FAOR with a high mass activity. The mass activity of NCCP for FAOR is 3 folds higher than the benchmark Palladium on Carbon (Pd/C, 10 wt%) catalyst. We reason this exceptionally high mass activity of NCCP to the synergetic effects between the surface decorated Pd nanoclusters and the transition metal cores, resulting in highly disturbed electronic configurations at the surface. In addition, the intriguing nanostructure evolved during FAOR can facilitate atomic, ionic, and molecular transfers during FAOR. The NCCP also demonstrates a high electrocatalytic stability for FAOR, which highlights its potential use for the practical DFAFC. [ABSTRACT FROM AUTHOR]