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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]

Exploring a new strategy for the removal of adsorbed CO (CO*) on a Pt surface at a low potential is the key to achieving enhanced catalysis for the formic acid oxidation reaction (FAOR); however, the development of such a strategy remains a significant challenge. Herein, we report a class of Au/PtCo heterojunction nanowires (HNWs) as efficient electrocatalysts for accelerating the FAOR. This heterojunction structure and the induced Co alloying effects can facilitate formic acid adsorption/activation on Pt with high CO tolerance, generating the FAOR pathway from dehydration to dehydrogenation. The optimized Au23/Pt63Co14 HNWs showed the highest specific and mass activities of 11.7 mA cm−2Pt and 6.42 A mg−1Pt reported to date, respectively, which are considerably higher than those of commercial Pt/C. DFT calculations confirmed that the electron-rich Au segment enhances the electronic activity of the PtCo NWs, which not only allows the construction of a highly efficient electron transfer channel for the FAOR but also suppresses CO formation.

• 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.

[Display omitted] Through a two-way control of hexadecyl trimethyl ammonium bromide (CTAB) and hydrochloric acid (HCl), the PdCu nanoalloys with branched structures are synthesized in one step by hydrothermal reduction and used as electrocatalysts for formic acid oxidation reaction (FAOR). In this two-way control strategy, the CTAB is used as a structure-oriented surfactant, while a certain amount of HCl is used to control the reaction kinetics for achieving gradual growth of multi-dendritic structures. The characterizations including scanning transmission electron microscope (STEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggest that PdCu nanoalloys with unique multi-dendritic branches have favorable electronic structure and lattice strain for electrocatalyzing the oxidation of formic acid. In specific, among the electrocatalysts with different Pd/Cu ratios, the Pd 1 Cu 1 branched nanoalloys have the largest electrochemically active surface area (ECSA) and the best performance for the FAOR. The catalytic activity of the Pd 1 Cu 1 branched nanoalloys is 2.4 times that of commercial Pd black. After the chronoamperometry test, the Pd 1 Cu 1 branched nanoalloys still maintain their original morphologies and higher current density than that of the commercial Pd black. In addition, in the CO-stripping tests, the initial oxidation potential and the oxidation peak potential of the PdCu branched nanoalloys for CO adsorption are lower than those of commercial Pd balck, evincing their better anti-poisoning performance. [ABSTRACT FROM AUTHOR]

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]

Pt-based catalysts have limited usefulness in direct formic acid fuel cells (DFAFCs) due to their susceptibility to CO poisoning. Combining Pt with Fe atoms is an effective approach for suppressing Pt poisoning by CO. In this work, we fabricate novel carbon-supported FePt alloy nanoparticles (FePt@C) by pyrolyzing Pt nanoparticles encapsulated within mesoporous MIL-101(Fe) (Pt@MIL-101(Fe)). The resulting FePt nanoparticles (Fe3Pt (111)) possess a lower CO adsorption energy (0.64 eV) than the (111) surfaces of Pt, indicating that the FePt nanoparticles are far less susceptible to CO poisoning. The mass activity and current density of a 9.6 wt% FePt@C catalyst are 4.2 and 4.5 times, respectively, higher than those of a commercial Pt/C catalyst. Furthermore, the 9.6 wt% FePt@C catalyst exhibits excellent durability, with only a 0.1% loss of mass activity after 1000 cycles. These results should guide the development of improved anode catalysts for DFAFCs based on MOF precursors.

Control of the composition and morphology of Pd‐based electrocatalysts is a promising strategy for the development of efficient direct formic acid fuel cells. Herein, a two‐step method is presented for the design of B‐doped PdCuAu nanospine assemblies (B‐PdCuAu NAs) using NaBH4 as the boron dopant. The boron content can be tailored easily by tuning the reaction time, and an optimal boron content is beneficial to promote the formic acid oxidation reaction. Such B‐PdCuAu NAs exhibit superior mass and specific activities to commercial Pd black and PdCuAu NAs in alkaline solution. The excellent catalytic performance of B‐PdCuAu NAs may arise from the increase in surface active sites and the electronic effect of boron modification. This work provides a facile synthesis of the B‐doped metallic catalysts and highlights the boron modification in improving their performance as anode electrocatalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO2 emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field.

In this study, we developed a carbon black (CB)-embedded carbon nanofiber (CNF) as a Pd support, which showed a high level of formic acid oxidation reaction (FAOR) activity. For the support preparation, heat treatment involving calcination at 1000 °C in a nitrogen atmosphere (carbonization) followed by calcination at 850 °C in water vapor (steam activation) was conducted to form a CB, which contained carbon nanofibers made from a polyacrolynitrile (PAN) fiber prepared by electrospinning. This catalyst showed a high level of FAOR activity. In this situation, the CB was also heat-treated, therefore, it was unclear whether the origin of the high FAOR activity of the CB-embedded CNF was caused by the CNF itself or the heat treatment of the CB. In order to establish the cause of the high FAOR activity of the CB-embedded CNF, the CBs underwent several heat treatments; i.e., stabilization, carbonization, and steam activation. Two types of carbon black with different pore structures, i.e., Ketjen black and Vulcan XC-72, were used to investigate the FAOR activity. The appropriate heat treatment of the CB promotes the improved FAOR activity; however, excessive heat treatment caused a deterioration in the FAOR activity, especially for Ketjen due to the presence of numerous micropores. However, by embedding the CB into the CNF, the FAOR activity improved, especially in the case of Ketjen, even though the embedded CB underwent several heat treatments. The optimum ratio of CB/PAN in the CB-embedded CNF was also investigated. The highest FAOR activity was observed at 0.25 CB/PAN for both the Vulcan and Ketjen. The electronic state of Pd3d in which the binding energy of the metallic Pd shifted to a lower binding energy suggested that the metal–support interaction is strong at the CB/PAN ratio of 0.25. On the basis of these results, it was found that heat treatment of the CB by embedding it in the CNF is a promising way to achieve a metal–support interaction without destroying its structure. [ABSTRACT FROM AUTHOR]

Unique and novel Pd 4 Sn nanochain networks were successfully synthesized with an average diameter of 5 nm, rendering a modified Pd electronic structure with rich defects such as atomic corners, steps or ledges as catalytic active sites for great enhancement of charge transfer and electrode kinetics. The prepared Pd 4 Sn nanochain networks held an electrochemically active surface area as high as 119.40 m 2  g −1 , and exhibited higher catalytic activity and stability toward formic acid oxidation compared with Pd 3 Sn nanochain networks, Pd 5 Sn nanochain networks, Pd 4 Sn dendrites and Pd/C. The fundamental insight of the enhancement mechanism is discussed, and this work offers a novel, less expensive but highly active catalyst for direct formic acid fuel cells. [ABSTRACT FROM AUTHOR]

The morphology- and size-tunable synthesis of nanocatalysts has attracted substantial research interest especially in catalysis. In this work, we synthesized free-standing Pd nanochain networks (Pd NCNs) and Pd nanodendrites (Pd NDs) through a direct poly- l -lysine (PLL)-mediated one-pot aqueous method. The presence of PLL and its concentrations were critical in this regard, showing PLL as the structure-directing and capping agents during the nucleation and crystal growth procedures. The synthesized architectures exhibited improved catalytic activity and enhanced durability towards formic acid oxidation and hydrogen evolution reactions relative to commercial Pd black catalyst. Moreover, the electrochemical active surface area and the electrocatalytic performance of Pd NCNs were dramatically enhanced in comparison to Pd NDs mainly owing to the unique network-like structure of Pd NCNs. [ABSTRACT FROM AUTHOR]

Bimetallic noble metal nanocrystals have been widely applied in many fields, which generally are synthesized by the wet-chemistry reduction method. This work presents a purposely designed atoms diffusion induced phase engineering of PtAu alloy nanocrystals on platy Au substrate (PtAu-on-Au nanostructures) through simple hydrothermal treatment. Benefitting from the synergistic effects of component and structure, PtAu-on-Au nanostructures remarkably enhance the dehydrogenation pathway of the formic acid oxidation reaction (FAOR), and thus exhibit much higher FAOR activity and durability compared with Pt nanocrystals on platy Au substrate (Pt-on-Au nanostructures) and commercial Pd black due to an excellent stability of platy Au substrate and a high oxidation resistance of PtAu alloy nanocrystals. The atoms diffusion-induced phase engineering demonstrated in this work builds a bridge between the traditional metallurgy and modern nanotechnologies, which also provides some useful insights in developing noble metals based alloyed nanostructures for the energy and environmental applications. [ABSTRACT FROM AUTHOR]

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]

The catalytic activity of novel 20% Pd Fe 3 O 4 /C catalyst for Formic Acid Oxidation Reaction (FAOR) in 0.5 mol L −1 H 2 SO 4 is reported. The evaluation has been carried out with several concentrations of the organic molecule (0.01, 0.1, 0.5 and 1 mol L −1 ). Electrochemical characterization shows lower specific current densities than those of a 20% Pd/C for the FAOR. Meanwhile, about a 2.6 increase in mass current density at Pd Fe 3 O 4 /C (441.67 mA mg Pd −1 ) is observed compared to the monometallic with 1 mol L −1 FA. The onset potential (E on-set ) for the FAOR is also more negative (0.1 V) at Pd Fe 3 O 4 /C. Economic magnetite may improve the performance of Pd-based anodes for the FAOR in terms of mass catalytic activity, but there is necessity to enhance the specific activity. [ABSTRACT FROM AUTHOR]

Herein, a one-pot co-reduction method was developed to prepare flower-like Au@AuPd core-shell nanocrystals (Au@AuPd NCs) under the guidance of 2,4-diamino-6-hydroxypyrimidine (DAHP). The product was mainly characterized by microscopic measurements, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis, and its formation mechanism was discussed in details. The architectures showed much larger electrochemical active surface area (62.68 m 2 g −1 Pd ) than commercial Pd black (8.23 m 2 g −1 Pd ), together with the higher mass activity (1250 mA mg −1 ) for formic acid oxidation reaction (FAOR). Besides, the catalyst displayed improved catalytic features for hydrogen evolution reaction (HER) relative to Pd black and Pt/C catalysts. These indicate the potential applications of the catalyst in energy storage and transformation. [ABSTRACT FROM AUTHOR]

The synthesis of Pd nanocrystals of controlled size and morphology has drawn enormous interest due to their catalytic activity. We report a new and efficient strategy for the one-step synthesis of monodispersed Pd nanocubes with ethylenediamine tetramethylene phosphonate (EDTMP) as a complex-forming and capping agent. The morphology, structure, and growth mechanism of the Pd nanocubes were fully characterized via selected area electron diffraction (SAED), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that the morphology of the Pd nanocrystals in the proposed EDTMP-PdCl system could be changed from octahedrons to nanocubes simply by adjusting the amount of iodide used during synthesis. After UV/ozone and electrochemical cleaning, the as-prepared Pd nanocubes demonstrated excellent electrocatalytic activity and stability during formic acid oxidation, owing to their abundant {100} facets and small particle size. [ABSTRACT FROM AUTHOR]

The carbon supporting materials play a crucial role for improving the utilization and electrocatalytic activity of noble metal nanocrystals. In this work, the high-quality carbon nanobowls (CNBs) with high surface area are synthesized successfully by a simple sol–gel synthetic method. Then, the as-prepared CNBs are used as advanced supporting material to anchor Pd nanocrystals by a facile homogeneous precipitation–reduction method. The as-prepared CNBs supported Pd nanocrystals (Pd/CNBs) nanohybrids are examined thoroughly by various physical characterizations. Physical measurements display that the CNBs facilitate the dispersion and anchorage of Pd nanocrystals due to their high surface area and abundant O-containing surface groups. Cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry measurements reveal that the Pd/CNBs nanohybrids have higher electrocatalytic activity and durability for the formic acid electro oxidation than Vulcan XC-72 carbon supported Pd nanocrystals (Pd/C-72) nanohybrids and commercial Pd/C electrocatalyst. [ABSTRACT FROM AUTHOR]

Nanostructured palladium (Pd) supported on carbon (Vulcan XC-72) substrate, prepared via carbonyl chemical route, showed Pd-mass depending morphology, reflected on the surface electrochemistry via cyclic, CO-stripping voltammograms, and performance in direct formic acid and direct methanol micro laminar flow fuel cell arrangement. Comparison was done with commercial Pd/C (30 wt.%, ETEK) catalyst. The formic acid oxidation reaction (FAOR) studied in different acid media (0.1 M HClO 4 , 0.5 M H 2 SO 4 and 0.5 M H 3 PO 4 ), indicated an enhanced FAOR activity on nanowire-like as compared to nanoparticles and nanorods as well as the commercial one in each electrolyte. Besides, the nanowire-like Pd/C catalyst also favored methanol (MOR) in 0.1 M KOH. These facts confirm favorable morphological effect of nanowires for organic fuel oxidation in both acid and alkaline media. [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]

The catalytic activity of Pd-CeO/C and non-supported Pd-CeO electrocatalysts for the formic acid (FAOR) and glycerol oxidation reaction (GOR) is evaluated in this work. The materials have been synthesized by pyrolysis in H atmosphere at 300 and 600 °C, with a nominal Pd:CeO ratio of 1:1. X-ray diffraction analysis demonstrates polycrystalline materials with particles sizes ranging from 11 to 14 nm (Pd) and 26 to 48 nm (CeO). Electrocatalytic measurements show a positive effect of dispersing the catalysts on Vulcan in the case of the FAOR, in terms of potential-current density profile and onset potential. While unsupported Pd-CeO nanoparticles behave poorly, the Pd-CeO/C anodes show a very high performance towards the FAOR. Particularly, Pd-CeO/C obtained at 600 °C shows a significantly high catalytic activity, with a higher mass current density than a comparable Pd/C electrocatalyst. X-ray photoelectron spectroscopy analysis undoubtedly demonstrates that the carbon support has an important effect on the oxidation states of Pd and CeO, which in turns influences positively the catalytic behavior of Pd-CeO/C catalysts. Furthermore, both supported and unsupported Pt-CeO materials have shown no catalytic activity for the GOR. The results indicate that Pd-CeO/C electrocatalysts can be considered as excellent candidate anodes for direct formic acid fuel cells. [ABSTRACT FROM AUTHOR]

By combining alloying and supporting approaches, ternary alloy CuFePt nanocatalysts anchored on the reduced graphene oxide (RGO) have been facilely synthesized by using NaBH 4 as reductant in an ambient one-pot strategy. The as-prepared CuFePt/RGO hybrids were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive spectrometry (EDS), and transmission electron microscopy (TEM). The electrochemical measurements showed that the ternary CuFePt/RGO exhibited a highly enhanced electrocatalytic activity and improved stability for the methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR), much superior to those of binary CuPt/RGO and FePt/RGO, and mono-metallic Pt/RGO counterparts. The atomic composition ratios of Cu and Fe in CuFePt/RGO were also optimized to probe their influences on electrocatalytic performance. The straightforward synthesis of ternary CuFePt/RGO provides a promising strategy for development of high-performance Pt alloy catalysts for both MOR and FAOR in fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: The nano-catalysts of Pd x Ni y bimetallic nanoparticles (NPs, the nominal atomic ratios of Pd to Ni are 2:1, 3:2 and 1:1) supported on multi-walled carbon nanotubes (MWCNTs) (denoted as Pd x Ni y /MWCNTs) have been synthesized by a thermal decomposition process using room temperature ionic liquids (RTILs) of N-butylpyridinium tetrafluoroborate (BPyBF4) as the solvent. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of the samples, revealing that the prepared Pd x Ni y NPs were quite uniformly dispersed on the surface of MWCNTs with an average particle size of ∼8.0 nm. Formic acid oxidation reaction (FAOR) was investigated on the as-prepared catalysts by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), demonstrating that the peak current on the Pd3Ni2/MWCNTs catalyst was about three times higher than that on the Pd/MWCNTs. The lower electrode potential and easier hydrogen evolution, based on the results obtained from chronopotentiometry and CV, respectively, were thought as the main reasons for the excellent electrocatalysis of the Pd3Ni2/MWCNTs toward formic acid oxidation reaction (FAOR) when compared to other samples. [Copyright &y& Elsevier]

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]

Abstract: The oleylamine (OAm)-functionalized Pd nanoparticles (Pd–OAm) have been conveniently synthesized through direct thermal decomposition method of low cost palladium acetate. The morphology, crystalline structure and composition of the Pd–OAm are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fourier transform infrared (FT-IR) spectroscopy, XPS and zeta potential analysis confirm the successful immobilization of OAm molecules on the Pd nanoparticles surface. The Pd–OAm displays an enhanced electrocatalytic activity and formic acid-tolerant ability for the oxygen reduction reaction (ORR), suggesting a potential application in cathodic catalyst for direct formic acid fuel cells. [Copyright &y& Elsevier]

Abstract: In this work, we conveniently synthesize the three-dimensionally (3D) networks-like palladium–cobalt alloy nanoassemblies (Pd–Co ANAs) through a simple simultaneous reduction reaction with sodium borohydride using inorganic K2PdCl4/K3Co(CN)6 cyanogel as reaction precursors, and clarify the formation mechanism of 3D networks structure and generation mechanism of Pd–Co alloy at room temperature. The morphology, structure, size and composition of the Pd–Co ANAs are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive spectrum (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry, chronoamperometry and CO-stripping voltammetry tests demonstrate the Pd–Co ANAs have higher electrocatalytic activity, better electrochemical stability, and higher resistance to CO poisoning over single-component Pd nanoparticles for the formic acid oxidation reaction (FAOR) owing to their unique 3D structure and alloy property. [Copyright &y& Elsevier]

Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO2 emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field. [ABSTRACT FROM AUTHOR]

The impact of solution pH has been investigated for the electrooxidation of formic acid on Au(111), taking the mole fraction of formate in solution as the relevant parameter. The electrocatalytic current density is increasing with rising pH and reaches a plateau for pH > 4. The pH-dependence of characteristic potentials shows systematic trends for the onset of the reaction, the peak maximum, and the phase transition within the formate adlayer. After the addition of phosphate buffer, a substantial deactivation by specific adsorption of phosphates and a bell-shaped curve for the maximum current density as a function of pH is found. The general behavior of co-adsorbing anions is addressed at low pH using various oxyanions to get more insight into the role of adsorbed formate. While non-carboxylate anions are displaced by formate at high potentials, mixed phases are observed for formate and other carboxylates. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A carbon-supported intermetallic FePt NP (9.6%FePt@C) catalyst is fabricated from MIL-101(Fe) and Pt nanoparticles. • The MOF pore restriction strategy limits the aggregation of Pt NPs. • The introduction of Fe can significantly enhance the resistance of Pt-based catalysts to CO poisoning. • Excellent activity and long-term stability for FAOR in acid medium. Pt-based catalysts have limited usefulness in direct formic acid fuel cells (DFAFCs) due to their susceptibility to CO poisoning. Combining Pt with Fe atoms is an effective approach for suppressing Pt poisoning by CO. In this work, we fabricate novel carbon-supported FePt alloy nanoparticles (FePt@C) by pyrolyzing Pt nanoparticles encapsulated within mesoporous MIL-101(Fe) (Pt@MIL-101(Fe)). The resulting FePt nanoparticles (Fe 3 Pt (1 1 1)) possess a lower CO adsorption energy (0.64 eV) than the (1 1 1) surfaces of Pt, indicating that the FePt nanoparticles are far less susceptible to CO poisoning. The mass activity and current density of a 9.6 wt% FePt@C catalyst are 4.2 and 4.5 times, respectively, higher than those of a commercial Pt/C catalyst. Furthermore, the 9.6 wt% FePt@C catalyst exhibits excellent durability, with only a 0.1% loss of mass activity after 1000 cycles. These results should guide the development of improved anode catalysts for DFAFCs based on MOF precursors. [ABSTRACT FROM AUTHOR]

Image, graphical abstract Faceting and nanostructuring of polycrystalline gold electrodes by cathodic corrosion in concentrated potassium hydroxide electrolytes has been systematically studied at different electrode potentials. Current-potential curves for the restructured Au electrodes in 0.1 M H 2 SO 4 show characteristics of Au(111) in the double-layer and oxidation region. Thus, the modified Au electrodes adopt properties typically known for well-defined single crystal surfaces. Besides the preferential surface faceting, the electrochemically active surface area (EASA) is enhanced as a function of potential, concentration and time. Scanning electron micrographs show the formation of triangular pits and nanostructures with a specific orientation confirming the formation of (111)-facets. In this way, the behavior of single crystals is accompanied with the properties of nanoparticles which are of utmost interest in electrocatalysis and surface-enhanced Raman spectroscopy (SERS). The electrocatalytic activity of the newly formed "Au(111)" surface from an Au wire has been tested towards the hydrogen evolution reaction (HER) and for the formic acid oxidation reaction (FAOR). The study of electrocatalytic reactions at these nanostructured electrodes allows to identify active centers, which are absent for extended single crystal surfaces. Adsorbed pyridine on the nanostructured Au electrodes directly shows SERS activity, while untreated polycrystalline Au is SERS-inactive. The use of cathodic corrosion of simple wires is a paradigm of SERS-applications in electrochemistry with clean Au electrodes that provide properties of Au(111) single crystals. [ABSTRACT FROM AUTHOR]

• Thermal annealing probing for performance enhancement of Pd/Fe catalysts. • Two kinds of active sites of Pd and Pd@FeP were indicated in Pd/FeP system. • Low active/unstable Pd could be transformed into more active Pd@FeP sites. • High catalytic activity/stability for formic acid oxidation was obtained. Thermal annealing is usually employed for performance enhancement of catalysts while the reason is still unclear. Herein, performance improvement of a promising Pd/FeP system via thermal annealing to provide enhanced active sites, as a proof of concept, was demonstrated for the formic acid oxidation reaction. Two kinds of active sites of Pd and Pd@FeP were indicated in Pd/FeP catalyst by the well-recognized CO stripping technique; the low active/unstable Pd sites could be transformed into more active Pd@FeP sites via thermal annealing and electrochemical reduction. The best catalytic activity of annealed Pd/FeP catalyst was 1.6 times of fresh Pd/FeP and 2.8 times of Pd/C catalysts. A maximum catalytic efficiency increased by 65 % was revealed owing to the Pd@FeP active sites formation; as high as 55 % of the initial current was maintained after the accelerated stability test for 1000 cycles. The result helps understand the thermal annealing effect on electro-catalyst performance improvement. [ABSTRACT FROM AUTHOR]

• The PdCuPt HZBUS were prepared by a one-pot wet-chemical approach. • PEO and KBr performed as co-directing agents in the synthesis. • The PdCuPt HZBUS provide enlarged surface area and more active sites. • The nanocatalyst displayed high activity and long-term stability for FAOR. Hierarchically branched multi-metallic nanoassembles are promising catalysts extensively used in catalytic fields because of their unique structural features and multicompositions advantages. Herein, three-dimensional (3D) hierarchical zigzag-branched urchin-like PdCuPt superstructures (HZBUS) were prepared by a one-pot wet-chemical method, where polyethylene oxide (PEO) and KBr served as directing agents. The specific architectures provided abundant active sites highly available for reactants, in turn showing highly enlarged electrochemically active surface area (16.79 m2 g−1 Pd). The as-obtained PdCuPt HZBUS displayed dramatically enhanced catalytic activity and improved long-term durability for formic acid oxidation reaction (FAOR), surpassing homemade PdCu nanoparticles (NPs), commercial Pd black and Pt/C catalysts. This work offers a new strategy for construction of advanced multimetallic electrocatalysts with charming superstructures and high-efficient performances in fuel cells. [ABSTRACT FROM AUTHOR]

The electronic interaction between metal and supports can regulate the activity of heterogeneous nanomaterials. We designed four supported Pd catalysts (Pd/ZnO, Pd/TiO 2 , Pd/Al 2 O 3 and Pd/SiO 2) for the electrocatalytic activity toward the formic acid oxidation reaction (FAOR). The electrochemical results demonstrate that Pd/ZnO exhibits superior electrocatalytic activity toward FAOR, which can be attributed to the decreased electron density of ZnO-supported Pd nanoparticles, as further confirmed by X-ray photoelectron spectroscopic characterization and CO stripping electrochemical measurement. This study provides an effective method for the design of high-efficiency electrocatalysts, which could be also useful for studying the surface electronics of supported metal-nanoparticle. Unlabelled Image • The electron density on the surface of Pd nanoparticles has an effect on its catalytic activity. • The electrocatalytic activity of Pd catalysts toward FAOR was regulated by using different supports through EMSI. • The superior electrocatalytic activity is owing to the lower electron density of Pd catalyst. [ABSTRACT FROM AUTHOR]