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A method is introduced to rapidly (<30 min) synthesize single metal nanoparticles with narrow size distribution in a simple way. It is based on the electrospraying of a metal precursor solution into a surfactant solution, which acts as a reducing and stabilizing agent. This synthesis method is demonstrated for the production of Ag and Au nanoparticles, which are incorporated onto carbonaceous and non-carbonaceous supports. The nanoparticle size depends on the internal diameter of the spraying nozzle. The removal of the stabilizing surfactant (dodecylamine; DDA) is also examined via thermal annealing and oxygen plasma treatments. Thermal annealing at a low temperature rate is found to be the most effective, as it completely removes DDA from the metal nanoparticles without inducing changes in their particle size. To verify that the supported Ag nanoparticles post calcination are surfactant-free and, thus, their surface sites are active, their oxygen reduction reaction (ORR) activity is measured in alkaline media, demonstrating similar values to the ones reported in the literature. [ABSTRACT FROM AUTHOR]

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Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO2 electrochemical reduction reaction (CO2RR) can contribute to the decarbonization of the global economy. Here, well‐defined Cu2O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu2O NCs, the catalyst with 5 at % Ag on Cu2O NCs displayed a two‐fold increase in the Faradaic efficiency for C2+ liquid products (30 % at −1.0 VRHE), including ethanol, 1‐propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X‐ray absorption spectroscopy revealed the partial reduction of Cu2O during CO2RR, accompanied by a reaction‐driven redispersion of Ag on the CuOx NCs. Data from operando surface‐enhanced Raman spectroscopy further uncovered significant variations in the CO binding to Cu, which were assigned to Ag−Cu sites formed during CO2RR that appear crucial for the C−C coupling and the enhanced yield of liquid products. [ABSTRACT FROM AUTHOR]

Identifying the structural response of nanoparticle–support ensembles to the reaction conditions is essential to determine their structure in the catalytically active state as well as to unravel the possible degradation pathways. In this work, we investigate the (electronic) structure of carbon- and oxide-supported Pt nanoparticles during electrochemical oxidation by in situ X-ray diffraction, absorption spectroscopy as well as the Pt dissolution rate by in situ mass spectrometry. We prepared ellipsoidal Pt nanoparticles by impregnation of the carbon and titanium-based oxide support as well as spherical Pt nanoparticles on an indium-based oxide support by a surfactant-assisted synthesis route. During electrochemical oxidation, we show that the oxide-supported Pt nanoparticles resist (bulk) oxide formation and Pt dissolution. The lattice of smaller Pt nanoparticles exhibits a size-induced lattice contraction in the as-prepared state with respect to bulk Pt but it expands reversibly during electrochemical oxidation. This expansion is suppressed for the Pt nanoparticles with a bulk-like relaxed lattice. We could correlate the formation of d-band vacancies in the metallic Pt with Pt lattice expansion. PtOx formation is strongest for platelet-like nanoparticles and we explain this with a higher fraction of exposed Pt(100) facets. Of all investigated nanoparticle–support ensembles, the structural response of RuO2/TiO2-supported Pt nanoparticles is the most promising with respect to their morphological and structural integrity under electrochemical reaction conditions. [ABSTRACT FROM AUTHOR]

Pt-based nanoparticles supported on carbon materials are state-of-the-art electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Interparticle distance and particle size of the supported nanoparticles play a crucial role for the catalyst’s performance. The synthesis approach of wet impregnation and thermal reduction in a regular static packed-bed tube furnace often results in poorly distributed Pt particles in terms of interparticle distance and particle size. Here, we report on a fluidized bed gas reduction reactor for the preparation of supported well-dispersed nanoparticles. To validate the reactor, we compared and contrasted Pt nanoparticle ensembles supported on Vulcan XC 72R prepared using a conventional, horizontal static packed bed tube furnace, and using our novel vertical fluidized bed reduction reactor. The catalysts were physico-chemically characterized and electrochemically tested with respect to their electrocatalytic oxygen reduction reaction reactivity using rotating disk electrode (RDE) experiments. Our results demonstrate that the nanoparticle samples prepared in the customized fluidized bed reduction reactor showed significantly superior mono-dispersion and more homogeneously spatial distribution that resulted in improved electrochemical stability [ABSTRACT FROM AUTHOR]

Shape controlled octahedral Pt-Ni alloy nanoparticles are promising oxygen reduction reaction (ORR) electrocatalysts for cathodes of low temperature Polymer Electrolyte Membrane fuel cells. Organic surfactants are used in order to control and tune particle composition, size, shape, and the distribution on the support material. Such methods request intense post-synthesis cleaning, or annealing procedures in order to remove the ligands, demanding for simpler cleaning and activation procedures. Here, we explore the effect of an acetic acid treatment of as-prepared Pt-Ni particles, applied prior to annealing. The resulting nanoparticles underwent an electrochemical surface characterization and were investigated in terms of their ORR activities and electrochemical long-term stability. After acid treatment the particles exhibit a Pt-rich surface, which changed slightly during annealing at 300°C but drastically to a more homogeneous alloy after annealing at 500°C due to Ni surface segregation. Besides changes in the (sub-)surface Pt and Ni composition, the octahedral shape did not survive the 500°C treatment. An improved ORR activity was obtained after annealing at 300°C. Our insights into effects and benefits of the described post-synthesis treatments aid our general understanding, but also may help improve the practical design of suitable treatment protocols of this class of ORR catalyst. [ABSTRACT FROM AUTHOR]

Carbon materials doped with nitrogen are active catalysts for the electrochemical two‐electron oxygen reduction reaction (ORR) to hydrogen peroxide. Insights into the individual role of the various chemical nitrogen functionalities in the H2O2 production, however, have remained scarce. Here, we explore a catalytically very active family of nitrogen‐doped porous carbon materials, prepared by direct pyrolysis of ordered mesoporous carbon (CMK‐3) with polyethylenimine (PEI). Voltammetric rotating ring‐disk analysis in combination with chronoamperometric bulk electrolysis measurements in electrolysis cells demonstrate a pronounced effect of the applied potentials, current densities, and electrolyte pH on the H2O2 selectivity and absolute production rates. H2O2 selectivity up to 95.3 % was achieved in acidic environment, whereas the largest H2O2 production rate of 570.1 mmol g−1catalyst h−1 was observed in neutral solution. X‐ray photoemission spectroscopy (XPS) analysis suggests a key mechanistic role of pyridinic‐N in the catalytic process in acid, whereas graphitic‐N groups appear to be catalytically active moieties in neutral and alkaline conditions. Our results contribute to the understanding and aid the rational design of efficient carbon‐based H2O2 production catalysts. Nitrogen‐doped porous carbon catalysts were prepared by using CMK‐3 and polyethylenimine, exhibiting high H2O2 selectivity of 95.3 % in acid, and a large production rate of 570.1 mmol gcat.−1 h−1 in neutral solution. Ex situ X‐ray photoemission spectroscopy analysis suggests a key mechanistic role of pyridinic‐N in acid, whereas graphitic‐N groups appear to be catalytically active moieties in neutral and alkaline conditions. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of degradation pathways of catalyst/support ensembles aids the development of rational strategies to improve their stability. Here, this is exemplified using indium tin oxide (ITO)‐supported Platinum nanoparticles as electrocatalysts at fuel cell (FC) cathodes under degradation protocols to mimic operating conditions in two potential regimes. The evolution of crystal structure, composition, crystallite and particle size is tracked by in situ X‐ray techniques (small and wide angle scattering), metal dissolution by in situ scanning flow cell coupled with mass spectrometry (SFC ICP‐MS) and Pt surface morphology by advanced electron microscopy. In a regular FC operation regime, Pt poisoning rather than Pt particle growth, agglomeration, dissolution or detachment was found to be the likely origin of the observed degradation and ORR activity losses. In the start‐up regime degradation is actually suppressed and only minor losses in catalytic activity are observed. The presented data thus highlight the excellent nanoparticle stabilization and corrosion resistance of the ITO support, yet point to a degradation pathway involving Pt surface modifications by deposition of sub‐monolayers of support metal ions. The identified degradation pathway of the Pt/oxide catalyst/support couple contributes to our understanding of cathode electrocatalysts for polymer electrolyte fuel cells (PEFC). [ABSTRACT FROM AUTHOR]

A key challenge of the carbon dioxide electroreduction (CO2RR) on Cu-based nanoparticles is its low faradic selectivity toward higher-value products such as ethylene. Here, we demonstrate a facile method for tuning the hydrocarbon selectivities on CuO x nanoparticle ensembles by varying the nanoparticle areal density. The sensitive dependence of the experimental ethylene selectivity on catalyst particle areal density is attributed to a diffusional interparticle coupling that controls the de- and re-adsorption of CO and thus the effective coverage of COad intermediates. Thus, higher areal density constitutes dynamically favored conditions for CO re-adsorption and *CO dimerization leading to ethylene formation independent of pH and applied overpotential. [ABSTRACT FROM AUTHOR]

LaNiO3 perovskite is an interesting precursor for Ni/L2O3 catalysts for the dry reforming of methane at high temperatures. Precursors have been synthesized by co-precipitation without, with 2.5 at%, and with 5 at% Ru doping. The presence of Ru leads to a stabilization of the perovskite structure and hinders the decomposition into NiO and Ruddlesden-Popper mixed oxides Lan+1NinO3n+1, which was observed for the Ru-free sample upon calcination at 1000 °C (n = 3). Upon reduction in hydrogen, a mechanism involving at least two steps was observed and the first major step was identified as the partial reduction of the precursor leading to a LaNiO2.5-like intermediate. The second major step is the reduction to Ni metal supported on L2O3 independent of the Ru content of the catalyst. In the presence of Ru, indications for Ni-Ru alloy formation and for a higher dispersion of the metallic phase were found. The catalytic activity in DRM of the catalyst containing 2.5% Ru was superior to the catalysts with more or without Ru. Furthermore, the propensity of coke formation was reduced by the presence of Ru. [ABSTRACT FROM AUTHOR]

Coking dynamics of Ni-based and Ni-free catalysts were studied in a magnetic suspension thermobalance under methane dry reforming conditions. Ni-rich catalysts undergo strong coking featured with a surface saturation point where the coking rate is drastically reduced. Catalyst resistance towards coking may be enhanced by using noble-metal-based Ni-free precursors or decreasing the Ni content in the catalytic system. The post reaction performed temperature-programmed oxidation experiment of the coked catalyst is diffusion-limited due to large amounts of formed carbon. [ABSTRACT FROM AUTHOR]

A Cu-based methanol synthesis catalyst was obtained from a phase pure Cu,Zn,Al hydrotalcite-like precursor, which was prepared by co-precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al2O3 catalyst. Upon thermal decomposition in air, the [(Cu0.5Zn0.17Al0.33)(OH)2(CO3)0.17] ⋅ mH2O precursor is transferred into a carbonate-modified, amorphous mixed oxide. The calcined catalyst can be described as well-dispersed 'CuO' within ZnAl2O4 still containing stabilizing carbonate with a strong interaction of Cu2+ ions with the Zn-Al matrix. The reduction of this material was carefully analyzed by complementary temperature-programmed reduction (TPR) and near-edge X-ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized CuI intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl2O4 spinel-like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less-embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings. [ABSTRACT FROM AUTHOR]

The catalytic performance of a Ni/MgAlOx catalyst was investigated in the high temperature CO2 reforming of CH4. The catalyst was developed using a Ni, Mg, Al hydrotalcite-like precursor obtained by co-precipitation. Despite the high Ni loading of 55 wt%, the synthesized Ni/MgAlOx catalyst possessed a thermally stable microstructure up to 900 °C with Ni nanoparticles of 9 nm. This stability is attributed to the embedding nature of the oxide matrix, and allows increasing the reaction temperature without losing active Ni surface area. To evaluate the effect of the reaction temperature on the reforming performance and the coking behavior, two different reaction temperatures (800 and 900 °C) were investigated. At both temperatures the prepared catalyst showed high rates of CH4 consumption. The higher temperature promotes the stability of the catalyst performance due to mitigation of the carbon formation. [ABSTRACT FROM AUTHOR]

Formal kinetic analysis of reduction process of the Cu-based layered double hydroxide -- LDH catalyst precursor for methanol synthesys was implemented. The process was studied by means of thermogravimetry (TG) and Differential scanning calorimetry (DSC) with respect to changes taking place in gas phase, which was analyzed by Massspectrometry (MS). The kinetic parameters of the non-isothermal reduction were determined and the rate limiting step was found. [ABSTRACT FROM AUTHOR]

One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al2O3 methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of nitrate (NO 3 - ) and nitrite (NO 2 - ) enables sustainable, carbon-neutral, and decentralized routes to produce ammonia (NH 3 ). Copper-based materials are promising electrocatalysts for NO x - conversion to NH 3 . However, the underlying reaction mechanisms and the role of different Cu species during the catalytic process are still poorly understood. Herein, by combining quasi in situ X-ray photoelectron spectroscopy (XPS) and operando X-ray absorption spectroscopy (XAS), we unveiled that Cu is mostly in metallic form during the highly selective reduction of NO 3 - /NO 2 - to NH 3 . On the contrary, Cu(I) species are predominant in a potential region where the two-electron reduction of NO 3 - to NO 2 - is the major reaction. Electrokinetic analysis and in situ Raman spectroscopy was also used to propose possible steps and intermediates leading to NO 2 - and NH 3 , respectively. This work establishes a correlation between the catalytic performance and the dynamic changes of the chemical state of Cu, and provides crucial mechanistic insights into the pathways for NO 3 - /NO 2 - electrocatalytic reduction.

The nature of the Cu-Zn interaction and especially the role of Zn in Cu/ZnO catalysts used for methanol synthesis from CO 2 hydrogenation are still debated. Migration of Zn onto the Cu surface during reaction results in a Cu-ZnO interface, which is crucial for the catalytic activity. However, whether a Cu-Zn alloy or a Cu-ZnO structure is formed and the transformation of this interface under working conditions demand further investigation. Here, ZnO/Cu 2 O core-shell cubic nanoparticles with various ZnO shell thicknesses, supported on SiO 2 or ZrO 2 were prepared to create an intimate contact between Cu and ZnO. The evolution of the catalyst's structure and composition during and after the CO 2 hydrogenation reaction were investigated by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct effect on the oxidation state of Zn, which, in turn, affects the catalytic performance. High Zn loadings, resulting in a stable ZnO catalyst shell, lead to increased methanol production when compared to Zn-free particles. Low Zn loadings, in contrast, leading to the presence of metallic Zn species during reaction, showed no significant improvement over the bare Cu particles. Therefore, our work highlights that there is a minimum content of Zn (or optimum ZnO shell thickness) needed to activate the Cu catalyst. Furthermore, in order to minimize catalyst deactivation, the Zn species must be present as ZnO x and not metallic Zn or Cu-Zn alloy, which is undesirably formed during the reaction when the precatalyst ZnO overlayer is too thin.

Electrochemical reduction of CO 2 (CO 2 RR) is an attractive technology to reintegrate the anthropogenic CO 2 back into the carbon cycle driven by a suitable catalyst. This study employs highly efficient multi-carbon (C 2+ ) producing Cu 2 O nanocubes (NCs) decorated with CO-selective Au nanoparticles (NPs) to investigate the correlation between a high CO surface concentration microenvironment and the catalytic performance. Structure, morphology and near-surface composition are studied via operando X-ray absorption spectroscopy and surface-enhanced Raman spectroscopy, operando high-energy X-ray diffraction as well as quasi in situ X-ray photoelectron spectroscopy. These operando studies show the continuous evolution of the local structure and chemical environment of our catalysts during reaction conditions. Along with its alloy formation, a CO-rich microenvironment as well as weakened average CO binding on the catalyst surface during CO 2 RR is detected. Linking these findings to the catalytic function, a complex compositional interplay between Au and Cu is revealed in which higher Au loadings primarily facilitate CO formation. Nonetheless, the strongest improvement in C 2+ formation appears for the lowest Au loadings, suggesting a beneficial role of the Au-Cu atomic interaction for the catalytic function in CO 2 RR. This study highlights the importance of site engineering and operando investigations to unveil the electrocatalyst's adaptations to the reaction conditions, which is a prerequisite to understand its catalytic behavior., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The hydrogenation of CO 2 to methanol over Cu/ZnO-based catalysts is highly sensitive to the surface composition and catalyst structure. Thus, its optimization requires a deep understanding of the influence of the pre-catalyst structure on its evolution under realistic reaction conditions, including the formation and stabilization of the most active sites. Here, the role of the pre-catalyst shape (cubic vs spherical) in the activity and selectivity of ZnO-supported Cu nanoparticles was investigated during methanol synthesis. A combination of ex situ , in situ , and operando microscopy, spectroscopy, and diffraction methods revealed drastic changes in the morphology and composition of the shaped pre-catalysts under reaction conditions. In particular, the rounding of the cubes and partial loss of the (100) facets were observed, although such motifs remained in smaller domains. Nonetheless, the initial pre-catalyst structure was found to strongly affect its subsequent transformation in the course of the CO 2 hydrogenation reaction and activity/selectivity trends. In particular, the cubic Cu particles displayed an increased activity for methanol production, although at the cost of a slightly reduced selectivity when compared to similarly sized spherical particles. These findings were rationalized with the help of density functional theory calculations.

Copper-based catalysts are established catalytic systems for the electrocatalytic CO 2 reduction reaction (CO 2 RR), where the greenhouse gas CO 2 is converted into valuable industrial chemicals, such as energy-dense C 2+ products, using energy from renewable sources. However, better control over the catalyst selectivity, especially at industrially relevant high current density conditions, is needed to expedite the economic viability of the CO 2 RR. For this purpose, bimetallic materials, where copper is combined with a secondary metal, comprise a promising and a highly tunable catalyst for the CO 2 RR. Nevertheless, the synergy between copper and the selected secondary metal species, the evolution of the bimetallic structural motifs under working conditions and the effect of the secondary metal on the kinetics of the Cu redox behavior require careful investigation. Here, we employ operando quick X-ray absorption fine structure (QXAFS) spectroscopy coupled with machine-learning based data analysis and surface-enhanced Raman spectroscopy (SERS) to investigate the time-dependent chemical and structural changes in catalysts derived from shape-selected ZnO/Cu 2 O nanocubes under CO 2 RR conditions at current densities up to -500 mA cm -2 . We furthermore relate the catalyst transformations observed under working conditions to the catalytic activity and selectivity and correlate potential-dependent surface and subsurface processes. We report that the addition of Zn to a Cu-based catalyst has a crucial impact on the kinetics of subsurface processes, while redox processes of the Cu surface layer remain largely unaffected. Interestingly, the presence of Zn was found to contribute to the stabilization of cationic Cu(i) species, which is of catalytic relevance since Cu(0)/Cu(i) interfaces have been reported to be beneficial for efficient electrocatalytic CO 2 conversion to complex multicarbon products. At the same time, we attribute the increase of the C 2+ product selectivity to the formation of Cu-rich CuZn alloys in samples with low Zn content, while Zn-rich alloy phases result in an increased formation of CO paralleled by an increase of the parasitic hydrogen evolution reaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Electrochemical reduction of carbon dioxide (CO 2 RR) is an attractive route to close the carbon cycle and potentially turn CO 2 into valuable chemicals and fuels. However, the highly selective generation of multicarbon products remains a challenge, suffering from poor mechanistic understanding. Herein, we used operando Raman spectroscopy to track the potential-dependent reduction of Cu 2 O nanocubes and the surface coverage of reaction intermediates. In particular, we discovered that the potential-dependent intensity ratio of the Cu-CO stretching band to the CO rotation band follows a volcano trend similar to the CO 2 RR Faradaic efficiency for multicarbon products. By combining operando spectroscopic insights with Density Functional Theory, we proved that this ratio is determined by the CO coverage and that a direct correlation exists between the potential-dependent CO coverage, the preferred C-C coupling configuration, and the selectivity to C 2+ products. Thus, operando Raman spectroscopy can serve as an effective method to quantify the coverage of surface intermediates during an electrocatalytic reaction., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO 2 electrochemical reduction reaction (CO 2 RR) can contribute to the decarbonization of the global economy. Here, well-defined Cu 2 O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu 2 O NCs, the catalyst with 5 at % Ag on Cu 2 O NCs displayed a two-fold increase in the Faradaic efficiency for C 2+ liquid products (30 % at -1.0 V RHE ), including ethanol, 1-propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X-ray absorption spectroscopy revealed the partial reduction of Cu 2 O during CO 2 RR, accompanied by a reaction-driven redispersion of Ag on the CuO x  NCs. Data from operando surface-enhanced Raman spectroscopy further uncovered significant variations in the CO binding to Cu, which were assigned to Ag-Cu sites formed during CO 2 RR that appear crucial for the C-C coupling and the enhanced yield of liquid products., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Adoption of proton exchange membrane (PEM) water electrolysis technology on a global level will demand a significant reduction of today's iridium loadings in the anode catalyst layers of PEM electrolyzers. However, new catalyst and electrode designs with reduced Ir content have been suffering from limited stability caused by (electro)chemical degradation. This has remained a serious impediment to a wider commercialization of larger-scale PEM electrolysis technology. In this combined DFT computational and experimental study, we investigate a novel family of iridium-niobium mixed metal oxide thin-film catalysts for the oxygen evolution reaction (OER), some of which exhibit greatly enhanced stability, such as minimized voltage degradation and reduced Ir dissolution with respect to the industry benchmark IrO x catalyst. More specifically, we report an unusually durable IrNbO x electrocatalyst with improved catalytic performance compared to an IrO x benchmark catalyst prepared in-house and a commercial benchmark catalyst (Umicore Elyst Ir75 0480) at significantly reduced Ir catalyst cost. Catalyst stability was assessed by conventional and newly developed accelerated degradation tests, and the mechanistic origins were analyzed and are discussed. To achieve this, the IrNbO x mixed metal oxide catalyst and its water splitting kinetics were investigated by a host of techniques such as synchrotron-based NEXAFS analysis and XPS, electrochemistry, and ab initio DFT calculations as well as STEM-EDX cross-sectional analysis. These analyses highlight a number of important structural differences to other recently reported bimetallic OER catalysts in the literature. On the methodological side, we introduce, validate, and utilize a new, nondestructive XRF-based catalyst stability monitoring technique that will benefit future catalyst development. Furthermore, the present study identifies new specific catalysts and experimental strategies for stepwise reducing the Ir demand of PEM water electrolyzers on their long way toward adoption at a larger scale.

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO 2 -decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO 2 promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg -1 Pd for SnO 2 @Pd NCs versus 0.42 A mg -1 Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO 2 -decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO 2 -decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO 2 provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnO x -decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)