Cyclic voltammetry, FTIRS, and DEMS study of the electrooxidation of carbon monoxide, formic acid, and methanol on cyanide-modified Pt(111) electrodes

Molecular Iridium Catalyzed Electrochemical Formic Acid Oxidation: Mechanistic Insights

Electrochemical formic acid oxidation reaction (FAOR) is a pivotal model for understanding organic fuel oxidation and advancing sustainable energy technologies. Here, we present mechanistic insights into a novel molecular-like iridium catalyst (Ir-N4-C) for FAOR. Our studies reveal that isolated sites facilitate a preferential dehydrogenation pathway, circumventing catalyst poisoning and exhibiting high inherent activity. In situ spectroscopic analyses elucidate that weakly adsorbed intermediates mediate the FAOR and are dynamically regulated by potential-dependent redox transitions. Theoretical and experimental investigations demonstrate a parallel mechanism involving two key intermediates with distinct pH and potential sensitivities. The rate-determining step is identified as the adsorption of formate via coupled or sequential proton-electron transfer, which aligns well with the observed kinetic properties, pH dependence, and hydrogen/deuterium isotope effects in experiments. These findings provide valuable insights into the reaction mechanism of FAOR, advancing our understanding at the molecular level and potentially guiding the design of efficient catalysts for fuel cells and electrolyzers.

Resolving Atomic-Scale Structure and Chemical Coordination in High-Entropy Alloy Electrocatalysts for Structure-Function Relationship Elucidation

The recent breakthrough in confining five or more atomic species in nanocatalysts, referred to as high-entropy alloy nanocatalysts (HEAs), has revealed the possibilities of multielemental interactions that can surpass the limitations of binary and ternary electrocatalysts. The wide range of potential surface configurations in HEAs, however, presents a significant challenge in resolving active structural motifs, preventing the establishment of structure-function relationships for rational catalyst design and optimization. We present a methodology for creating sub-5 nm HEAs using an aqueous-based peptide-directed route. Using a combination of pair distribution function and X-ray absorption spectroscopy, HEA structure models are constructed from reverse Monte Carlo modeling of experimental data sets and showcase a clear peptide-induced influence on atomic-structure and chemical miscibility. Coordination analysis of our structure models facilitated the construction of structure-function correlations applied to electrochemical methanol oxidation reactions, revealing the complex interplay between multiple metals that leads to improved catalytic properties. Our results showcase a viable strategy for elucidating structure-function relationships in HEAs, prospectively providing a pathway for future materials design.

Sub-Monolayer SbOx on PtPb/Pt Nanoplate Boosts Direct Formic Acid Oxidation Catalysis

To promote the commercialization of direct formic acid fuel cell (DFAFC), it is vital to explore new types of direct formic acid oxidation (FAOR) catalysts with high activity and direct pathway. Here, we report the synthesis of intermetallic platinum-lead/platinum nanoplates inlaid with sub-monolayer antimony oxide surface (PtPb/Pt@sub-SbOx NPs) for efficient catalytic applications in FAOR. Impressively, they can achieve the remarkable FAOR specific and mass activities of 28.7 mA cm-2 and 7.2 A mgPt-1, which are 151 and 60 times higher than those of the state-of-the-art commercial Pt/C, respectively. Furthermore, the X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results collectively reveal the optimization of the local coordination environment by the surface sub-monolayer SbOx, along with the electron transfer from Pb and Sb to Pt, driving the predominant dehydrogenation process. The sub-monolayer SbOx on the surface can effectively attenuate the CO generation, largely improving the FAOR performance of PtPb/Pt@sub-SbOx NPs. This work develops a class of high-performance Pt-based anodic catalyst for DFAFC via constructing the unique intermetallic core/sub-monolayer shell structure.

Electro-assisted methane oxidation to formic acid via in-situ cathodically generated H2O2 under ambient conditions

Direct partial oxidation of methane to liquid oxygenates has been regarded as a potential route to valorize methane. However, CH4 activation usually requires a high temperature and pressure, which lowers the feasibility of the reaction. Here, we propose an electro-assisted approach for the partial oxidation of methane, using in-situ cathodically generated reactive oxygen species, at ambient temperature and pressure. Upon using acid-treated carbon as the electrocatalyst, the electro-assisted system enables the partial oxidation of methane in an acidic electrolyte to produce oxygenated liquid products. We also demonstrate a high production rate of oxygenates (18.9 μmol h-1) with selective HCOOH production. Mechanistic analysis reveals that reactive oxygen species such as ∙OH and ∙OOH radicals are produced and activate CH4 and CH3OH. In addition, unstable CH3OOH generated from methane partial oxidation can be additionally reduced to CH3OH on the cathode, and so-produced CH3OH is further oxidized to HCOOH, allowing selective methane partial oxidation.

Highly Selective Synthesis of Monoclinic-Phased Platinum-Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis

Designing efficient formic acid oxidation reaction (FAOR) catalysts with remarkable membrane electrode assembly (MEA) performance in a direct formic acid fuel cell (DFAFC) medium is significant yet challenging. Herein, we report that the monoclinic-phased platinum-tellurium nanotrepang (m-PtTe NT) can be adopted as a highly active, selective, and stable FAOR catalyst with a desirable direct reaction pathway. The m-PtTe NT exhibits the high specific and mass activities of 6.78 mA cm^-2 and 3.2 A mg_Pt^-1, respectively, which are 35.7/22.9, 2.8/2.6, and 3.9/2.9 times higher than those of commercial Pt/C, rhombohedral-phased Pt₂Te₃ NT (r-Pt₂Te₃ NT), and trigonal-phased PtTe₂ NT (t-PtTe₂ NT), respectively. Simultaneously, the highest reaction tendency for the direct FAOR pathway and the best tolerance to poisonous CO intermediate can also be realized by m-PtTe NT. More importantly, even in a single-cell medium, the m-PtTe NT can display a much higher MEA power density (171.4 mW cm^-2) and stability (53.2% voltage loss after 5660 s) than those of commercial Pt/C, demonstrating the great potential in operating DFAFC device. The in-situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy jointly demonstrate that the unique nanostructure of m-PtTe NT can effectively optimize dehydrogenation steps and inhibit the CO intermediate adsorption, as well as promote the oxidation of noxious CO intermediate, thus achieving the great improvement of FAOR activity, poisoning tolerance, and stability. Density functional theory calculations further reveal that the direct pathway is the most favorable on m-PtTe NT than r-Pt₂Te₃ NT and t-PtTe₂ NT. The higher activation energy to produce CO and the relatively weaker binding with CO of m-PtTe NT result in the better CO tolerance. This work achieves remarkable FAOR and MEA performances of advanced Pt-based anodic catalysts for DFAFCs via a phase engineering strategy.

Alloying with Mn Enhances the Activity and Durability of the CoPt Catalyst toward the Methanol Oxidation Reaction

To improve the catalytic performance and durability of Pt catalysts used for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs), alloying of Pt with other transition metals such as Ru, Co, Ni, and Fe is considered an effective approach. Despite the significant progress made in the preparation of bimetallic alloys and their utilization for MOR, improving the activity and durability of the catalysts to make them commercially viable remains a stiff challenge. In this work, trimetallic Pt_100-x(MnCo)_x (16 < x < 41) catalysts were successfully synthesized via borohydride reduction followed by hydrothermal treatment at 150 °C. The electrocatalytic performance of the synthesized trimetallic Pt_100-x(MnCo)_x (16 < x < 41) catalysts toward MOR was studied using cyclic voltammetry and chronoamperometry. The results affirm that all Pt_100-x(MnCo)_x (16 < x < 41) alloys have superior MOR activity and durability as compared to bimetallic PtCo alloys and commercially available Pt/C (comm. Pt/C) catalysts. Among all the compositions studied, the Pt₆₀Mn_1.7Co_38.3/C catalyst exhibited superior mass activity (1.3 and 1.9 times higher than those of Pt₈₁Co₁₉/C and comm. Pt/C, respectively) toward MOR. Furthermore, all the newly synthesized Pt_100-x(MnCo)_x/C (16 < x < 41) catalysts showed better CO tolerance when compared with comm. Pt/C. This improved performance of the Pt_100-x(MnCo)_x/C (16 < x < 41) catalyst can be attributed to the synergistic effect of Co and Mn on the Pt lattice.

Kinetics of formic acid dehydration on Pt electrodes by time-resolved ATR-SEIRAS

The potential dependence of the rate of dehydration of formic acid to adsorbed CO (CO_ad) on Pt at pH 1 has been studied on a polycrystalline Pt surface by time-resolved surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) with simultaneous recording of current transients after a potential step. A range of formic acid concentrations has been used to obtain a deeper insight into the mechanism of the reaction. The experiments have allowed us to confirm that the potential dependence of the rate of dehydration has a bell shape, going through a maximum around the potential of zero total charge (pztc) of the most active site. The analysis of the integrated intensity and frequency of the bands corresponding to CO_L and CO_B/M shows a progressive population of the active sites on the surface. The observed potential dependence of the rate of formation of CO_ad is consistent with a mechanism in which the reversible electroadsorption of HCOO_ad is followed by its rate-determining reduction to CO_ad.

Correlations between experiments and simulations for formic acid oxidation

Electrocatalytic conversion of formic acid oxidation to CO₂ and the related CO₂ reduction to formic acid represent a potential closed carbon-loop based on renewable energy. However, formic acid fuel cells are inhibited by the formation of site-blocking species during the formic acid oxidation reaction. Recent studies have elucidated how the binding of carbon and hydrogen on catalyst surfaces promote CO₂ reduction towards CO and formic acid. This has also given fundamental insights into the reverse reaction, i.e. the oxidation of formic acid. In this work, simulations on multiple materials have been combined with formic acid oxidation experiments on electrocatalysts to shed light on the reaction and the accompanying catalytic limitations. We correlate data on different catalysts to show that (i) formate, which is the proposed formic acid oxidation intermediate, has similar binding energetics on Pt, Pd and Ag, while Ag does not work as a catalyst, and (ii) *H adsorbed on the surface results in *CO formation and poisoning through a chemical disproportionation step. Using these results, the fundamental limitations can be revealed and progress our understanding of the mechanism of the formic acid oxidation reaction.

Activity Quantification of Fuel Cell Catalysts via Sequential Poisoning by Multiple Reaction Inhibitors

The development of non-Pt or carbon-based catalysts for anion exchange membrane fuel cells (AEMFCs) requires identification of the active sites of the catalyst. Since not only metals but also carbon materials exhibit oxygen reduction reaction (ORR) activity in alkaline conditions, the contribution of carbon-based materials to ORR performance should also be thoroughly analyzed. However, the conventional CN^- poisoning experiments, which are mainly used to explain the main active site of M-N-C catalysts, are limited to only qualitative discussions, having the potential to make fundamental errors. Here, we report a modified electrochemical analysis to quantitatively investigate the contribution of the metal and carbon active sites to ORR currents at a fixed potential by sequentially performing chronoamperometry with two reaction inhibitors, CN^- and benzyl trimethylammonium (BTMA⁺). As a result, we discover how to quantify the individual contributions of two active sites (Pt nanoparticles and carbon support) of carbon-supported Pt (Pt/C) nanoparticles as a model catalyst. This study is expected to provide important clues for the active site analysis of carbon-supported non-Pt catalysts, such as M-N-C catalysts composed of heterogeneous elements.

How palladium inhibits CO poisoning during electrocatalytic formic acid oxidation and carbon dioxide reduction

Development of reversible and stable catalysts for the electrochemical reduction of CO₂ is of great interest. Here, we elucidate the atomistic details of how a palladium electrocatalyst inhibits CO poisoning during both formic acid oxidation to carbon dioxide and carbon dioxide reduction to formic acid. We compare results obtained with a platinum single-crystal electrode modified with and without a single monolayer of palladium. We combine (high-scan-rate) cyclic voltammetry with density functional theory to explain the absence of CO poisoning on the palladium-modified electrode. We show how the high formate coverage on the palladium-modified electrode protects the surface from poisoning during formic acid oxidation, and how the adsorption of CO precursor dictates the delayed poisoning during CO₂ reduction. The nature of the hydrogen adsorbed on the palladium-modified electrode is considerably different from platinum, supporting a model to explain the reversibility of this reaction. Our results help in designing catalysts for which CO poisoning needs to be avoided.

Enhanced electrocatalytic activity of Cu-modified, high-index single Pt NPs for formic acid oxidation

A key goal of nanoparticle-based catalysis research is to correlate the structure of nanoparticles (NPs) to their catalytic function. The most common approach for achieving this goal is to synthesize ensembles of NPs, characterize the ensemble, and then evaluate its catalytic properties. This approach is effective, but it excludes the certainty of structural heterogeneity in the NP ensemble. One means of addressing this shortcoming is to carry out analyses on individual NPs. This approach makes it possible to establish direct correlations between structures of single NPs and, in the case reported here, their electrocatalytic properties. Accordingly, we report on enhanced electrocatalytic formic acid oxidation (FAO) activity using individual Cu-modified, high-indexed Pt NPs. The results show that the Cu-modified Pt NPs exhibit significantly higher currents for FAO than the Pt-only analogs. The increased activity is enabled by the Cu submonolayer on the highly stepped Pt surface, which enhances the direct FAO pathway but not the indirect pathway which proceeds via surface-absorbed CO*.

Single-crystal Pt nanoparticles with a diameter of ∼200 nm were electrosynthesized, covered with a single monolayer of Cu, and then fully characterized. The resulting materials exhibit excellent electrocatalytic properties for formic acid oxidation.

Accelerated interfacial proton transfer for promoting the electrocatalytic activity

Interfacial pH is critical to electrocatalytic reactions involving proton-coupled electron transfer (PCET) processes, and maintaining an optimal interfacial pH at the electrochemical interface is required to achieve high activity. However, the interfacial pH varies inevitably during the electrochemical reaction owing to slow proton transfer at the interfacial layer, even in buffer solutions. It is therefore necessary to find an effective and general way to promote proton transfer for regulating the interfacial pH. In this study, we propose that promoting proton transfer at the interfacial layer can be used to regulate the interfacial pH in order to enhance electrocatalytic activity. By adsorbing a bifunctional 4-mercaptopyridine (4MPy) molecule onto the catalyst surface via its thiol group, the pyridyl group can be tethered on the electrochemical interface. The pyridyl group acts as both a good proton acceptor and donor for promoting proton transfer at the interfacial layer. Furthermore, the pK_a of 4MPy can be modulated with the applied potentials to accommodate the large variation of interfacial pH under different current densities. By in situ electrochemical surface-enhanced Raman spectroscopy (in situ EC-SERS), we quantitatively demonstrate that proton transfer at the interfacial layer of the Pt catalyst coated with 4MPy (Pt@4MPy) remains ideally thermoneutral during the H⁺ releasing electrocatalytic oxidation reaction of formic acid (FAOR) at high current densities. Thus, the interfacial pH is controlled effectively. In this way, the FAOR apparent current measured from Pt@4MPy is twice that measured from a pristine Pt catalyst. This work establishes a general strategy for regulating interfacial pH to enhance the electrocatalytic activities.

Adsorbing 4MPy on Pt surface promotes proton transfer at the interfacial layer, maintaining an optimal interfacial pH and promotes electrocatalytic reactions involving proton-coupled electron transfer (PCET) processes.

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid-phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure-performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini-review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.

Improved Rate for the Oxygen Reduction Reaction in a Sulfuric Acid Electrolyte using a Pt(111) Surface Modified with Melamine

The feasible commercialization of alkaline, phosphoric acid and polymer electrolyte membrane fuel cells depends on the development of oxygen reduction reaction (ORR) electrocatalysts with improved activity, stability, and selectivity. The rational design of surfaces to ensure these improved ORR catalytic requirements relies on the so-called "descriptors" (e.g., the role of covalent and noncovalent interactions on platinum surface active sites for ORR). Here, we demonstrate that through the molecular adsorption of melamine onto the Pt(111) surface [Pt(111)-M_ad], the activity can be improved by a factor of 20 compared to bare Pt(111) for the ORR in a strongly adsorbing sulfuric acid solution. The M_ad moieties act as "surface-blocking bodies," selectively hindering the adsorption of (bi)sulfate anions (well-known poisoning spectator of the Pt(111) active sites) while the ORR is unhindered. This modified surface is further demonstrated to exhibit improved chemical stability relative to Pt(111) patterned with cyanide species (CN_ad), previously shown by our group to have a similar ORR activity increase compared to bare Pt(111) in a sulfuric acid electrolyte, with Pt(111)-M_ad retaining a greater than ninefold higher ORR activity relative to bare Pt(111) after extensive potential cycling as compared to a greater than threefold higher activity retained on a CN_ad-covered Pt(111) surface. We suggest that the higher stability of the Pt(111)-M_ad interface stems from melamine's ability to form intermolecular hydrogen bonds, which effectively turns the melamine molecules into larger macromolecular entities with multiple anchoring sites and thus more difficult to remove.

Recent advances in formic acid electro-oxidation: from the fundamental mechanism to electrocatalysts

Direct formic acid fuel cells have attracted significant attention because of their low fuel crossover, high safety, and high theoretical power density among all the proton-exchange membrane fuel cells. Much effort has been devoted to the study of formic acid oxidation, including the reaction processes and electrocatalysts. However, as a model reaction, the anodic electro-oxidation process of formic acid is still not very clear, especially regarding the confirmation of the intermediates, which is not helpful for the design and synthesis of high-performance electrocatalysts for formic acid oxidation or conducive to understanding the reaction mechanisms of other small fuel molecules. Herein, we briefly review the recent advances in investigating the mechanism of formic acid electro-oxidation and the basic design concepts of formic acid oxidation electrocatalysts. Rather than an exhaustive overview of all aspects of this topic, this mini-review mainly outlines the progress of this field in recent years.

Tailored electrocatalysts by controlled electrochemical deposition and surface nanostructuring

Controlled electrodeposition and surface nanostructuring are very promising approaches to tailor the structure of the electrocatalyst surface, with the aim to enhance their efficiency for sustainable energy conversion reactions. In this highlight, we first summarise different strategies to modify the structure of the electrode surface at the atomic and sub-monolayer level for applications in electrocatalysis. We discuss aspects such as structure sensitivity and electronic and geometric effects in electrocatalysis. Nanostructured surfaces are finally introduced as more scalable electrocatalysts, where morphology, cluster size, shape and distribution play an essential role and can be finely tuned. Controlled electrochemical deposition and selective engineering of the surface structure are key to design more active, selective and stable electrocatalysts towards a decarbonised energy scheme.

Toward Overcoming the Challenges in the Comparison of Different Pd Nanocatalysts: Case Study of the Ethanol Oxidation Reaction

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature.

Multilayer electrodeposition of Pt onto 1-2 nm Au nanoparticles using a hydride-termination approach

Here we report on hydride-terminated (HT) electrodeposition of Pt multilayers onto ∼1.6 nm Au nanoparticles (NPs). The results build on our earlier findings regarding electrodeposition of a single monolayer of Pt onto Au NPs and reports relating to HT Pt electrodeposition onto bulk Au. In the latter case, it was found that electrodeposition of Pt from a solution containing PtCl42- can be limited to a single monolayer of Pt atoms if it is immediately followed by adsorption of a monolayer of H atoms. The H-atom capping layer prevents deposition of Pt multilayers. In the present report we are interested in comparing the structure of NPs after multiple HT Pt electrodeposition cycles to the bulk analog. The results indicate that a greater number of HT Pt cycles are required to electrodeposit both a single Pt monolayer and Pt multilayers onto these Au NPs compared to bulk Au. Additionally, detailed structural analysis shows that there are fundamental differences in the structures of the AuPt materials depending on whether they are prepared on Au NPs or bulk Au. The resulting structures have a profound impact on formic acid oxidation electrocatalysis.

Phase diagrams and dynamical evolution of the triple-pathway electro-oxidation of formic acid on platinum

A detailed numerical study including stability phase diagrams for the dynamical evolution of the electro-oxidation of formic acid on platinum was reported. The study evidences the existence of intertwined stability phases and the absence of chaos.

Microstructural Evolution of Au@Pt Core-Shell Nanoparticles under Electrochemical Polarization

Understanding the microstructural evolution of bimetallic Pt nanoparticles under electrochemical polarization is critical to developing durable fuel cell catalysts. In this work, we develop a colloidal synthetic method to generate core-shell Au@Pt nanoparticles of varying surface Pt coverages to understand how as-synthesized bimetallic microstructure influences nanoparticle structural evolution during formic acid oxidation. By comparing the electrochemical and structural properties of our Au@Pt core-shells with bimetallic AuPt alloys at various stages in catalytic cycling, we determine that these two structures evolve in divergent ways. In core-shell nanoparticles, Au atoms from the core migrate outward onto the surface, generating transient "single-atom" Pt active sites with high formic acid oxidation activity. Metal migration continues until Pt is completely encapsulated by Au, and catalytic reactivity ceases. In contrast, AuPt alloys undergo surface dealloying and significant leaching of Pt out of the nanoparticle. Elucidating the dynamic restructuring processes responsible for high electrocatalytic reactivity in Pt bimetallic structures will enable better design and predictive synthesis of nanoparticle catalysts that are both active and stable.

Tweaking the Interplay among Galvanic Exchange, Oxidative Etching, and Seed-Mediated Deposition toward Architectural Control of Multimetallic Nanoelectrocatalysts

Nanoscale galvanic exchange confined by metallic nanoparticles is an intriguing structure-remodeling process that transforms geometrically simple solid nanoparticles into multimetallic hollow nanoparticles with increased structural complexity and compositional diversity. Using liquid polyols with intrinsic reducing capabilities as the reaction medium for nanoparticle-templated galvanic exchange represents an interesting paradigm shift, allowing us to interface galvanic exchange with oxidative etching and seed-mediated deposition without introducing any additional oxidizing or reducing agents. By kinetically maneuvering the interplay among galvanic Cu-Pt exchange, oxidative Cu etching, and seed-mediated Pt deposition, we have been able to selectively transform AuCu₃ alloy nanoparticles into two architecturally distinct multimetallic heteronanostructures, namely, Au-Pt alloy skin-covered spongy nanoparticles and Pt nanodendrite-covered hollow nanoparticles, both of which exhibit unique structural features highly desirable for high-performance electrocatalysis. Using the formic acid oxidation and hydrogen evolution reactions in acidic electrolytes as model electrocatalytic reactions, we show that the multimetallic nanoparticles derived from AuCu₃ alloy nanoparticles through polyol-mediated galvanic exchange reactions markedly outperform the commercial Pt/C benchmark catalysts in terms of both activity and durability. This work not only provides important mechanistic insights on how galvanic exchange dynamically interplays with other redox processes to rigorously dictate the versatile structural transformations of multimetallic nanoparticles but also sheds light on the detailed structure-property relationships underpinning the intriguing electrocatalytic behaviors of architecturally complex multimetallic heteronanostructures.

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

The identification of active sites in electrocatalytic reactions is part of the elucidation of mechanisms of catalyzed reactions on solid surfaces. However, this is not an easy task, even for apparently simple reactions, as we sometimes think the oxidation of adsorbed CO is. For surfaces consisting of non-equivalent sites, the recognition of specific active sites must consider the influence that facets, as is the steps/defect on the surface of the catalyst, cause in its neighbors; one has to consider the electrochemical environment under which the "active sites" lie on the surface, meaning that defects/steps on the surface do not partake in chemistry by themselves. In this paper, we outline the recent efforts in understanding the close relationships between site-specific and the overall rate and/or selectivity of electrocatalytic reactions. We analyze hydrogen adsorption/desorption, and electro-oxidation of CO, methanol, and ammonia. The classical topic of asymmetric electrocatalysis on kinked surfaces is also addressed for glucose electro-oxidation. The article takes into account selected existing data combined with our original works.

Golden single-atomic-site platinum electrocatalysts

Bimetallic nanoparticles with tailored structures constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Here we report a facile colloidal method to prepare a series of platinum-gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly Pt₄Au₉₆, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid. A high forward current density of 3.77 A mg_Pt^-1 was observed for Pt₄Au₉₆, a value two orders of magnitude greater than those observed for core-shell structured Pt₇₈Au₂₂ and a commercial Pt nanocatalyst. Extensive structural characterization and theoretical density functional theory simulations of the best-performing catalysts revealed densely packed single-atom Pt surface sites surrounded by Au atoms, which suggests that their superior catalytic activity and selectivity could be attributed to the unique structural and alloy-bonding properties of these single-atomic-site catalysts.

Correlation between Formic Acid Oxidation and Oxide Species on Pt(Bi)/GC and Pt/GC Electrode through the Effect of Forward Potential Scan Limit

Following earlier works from our laboratory, further experiments on electrochemical behavior in formic acid oxidation at electrodeposited Pt(Bi)/GC and Pt/GC electrode were performed in order to examine the effect of successive increase of the forward potential scan limit. Correlation between formic acid oxidation and oxide species on Pt(Bi)/GC electrode with increases of forward potential scan limit is based on the dependency of the backward peak potential from backward peak current. The obtained dependency reveals Bi influence for the scan limits up to 0.8 V. Since the Pt(Bi)/GC electrode is composed of Bi core occluded by Pt and Bi-oxide surface layer, the observed behavior is explained through the influence of surface metal oxide on easier formation of OHad species. Nevertheless, the influence of electronic modification of Pt surface atoms by underlying Bi is present and leads to the stronger adsorption of OH on Pt. At higher forward potential scan limits (from 0.8 V), Pt has a dominant role in HCOOH oxidation.

Ultra-small Tetrametallic Pt-Pd-Rh-Ag Nanoframes with Tunable Behavior for Direct Formic Acid/Methanol Oxidation

Reversible tuning of ultra-small multimetallic Pt-Pd-Rh-Ag nanoframes is achieved. These nanoframes showed tunable and reversible modes for the oxidation of small organic molecules by simply inducing segregation with adsorbates, such as SO₄^2- and OH^- . This is the first example of reversible segregation under electrocatalytic conditions in atomic-sized electrocatalysts. These nanoframes also showed a controllable activity and good stability for the oxidation of small organic molecules.