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Electrochemical CO2 reduction represents a promising path toward the production of value-added chemicals. Atomically dispersed metal sites on nitrogen-doped carbon have demonstrated outstanding catalytic performance in this reaction. However, challenges remain in developing such catalysts beyond transition metals. Herein, we present two types of p-block indium single-atom catalysts: one with four nitrogen coordinated (In–N4) and another with three nitrogen coordinated with one vacancy nearby (In–N3–V). In electrochemical CO2 reduction, the In–N3–V site can achieve maximum CO Faradic efficiency (FECO) of 95% at −0.57 V vs reversible hydrogen electrode (RHE) in an aqueous medium. This outperforms the intact In–N4 catalyst with the maximum FECO of 80% at −0.47 V vs RHE. Density functional theory calculations on the mechanism suggest that structural change from In–N4 to In–N3–V brings the In orbital (s and pz) energies closer to the Fermi energy. These hybridized orbitals are responsible for lowering the energy barrier for COOH* intermediate formation, thus enhancing the catalytic performance. This work sheds light on the relationship between catalytic performance and structure of In single-atom sites, highlighting the importance of tailoring the electron state of s and pz orbitals in developing efficient p-block single-atom catalysts for electrochemical CO2 reduction. Electrochemical CO2 reduction represents a promising path toward the production of value-added chemicals. Atomically dispersed metal sites on nitrogen-doped carbon have demonstrated outstanding catalytic performance in this reaction. However, challenges remain in developing such catalysts beyond transition metals. Herein, we present two types of p-block indium single-atom catalysts: one with four nitrogen coordinated (In-N-4) and another with three nitrogen coordinated with one vacancy nearby (In-N-3-V). In electrochemical CO2 reduction, the In-N-3-V site can achieve maximum CO Faradic efficiency (FECO) of 95% at -0.57 V vs reversible hydrogen electrode (RHE) in an aqueous medium. This outperforms the intact In-N-4 catalyst with the maximum FE(CO )of 80% at -0.47 V vs RHE. Density functional theory calculations on the mechanism suggest that structural change from In-N-4 to In-N-3-V brings the In orbital (s and pz) energies closer to the Fermi energy. These hybridized orbitals are responsible for lowering the energy barrier for COOH* intermediate formation, thus enhancing the catalytic performance. This work sheds light on the relationship between catalytic performance and structure of In single-atom sites, highlighting the importance of tailoring the electron state of s and P-z orbitals in developing efficient p-block single-atom catalysts for electrochemical CO2 reduction.

Electrocatalytic oxidation of glycerol (EOG) is an attractive approach to convert surplus glycerol to value-added products. Experiments have shown that EOG activity and selectivity depend not only on the electrocatalyst but also on the electrode potential, the pH, and the electrolyte. For broadly employed gold (Au) electrocatalysts, experiments have demonstrated high EOG activity under alkaline conditions with glyceric acid as a primary product, whereas under acidic and neutral conditions Au is almost inactive producing only small amounts of dihydroxyacetone. In the present computational work, we have performed an extensive mechanistic study to understand the pH and potential dependency of Au-catalyzed EOG. Our results show that activity and selectivity are controlled by the presence of surface-bound hydroxyl groups. Under alkaline conditions and close to the experimental onset potential, modest OH coverage is preferred according to our constant potential calculations. This indicates that both Au(OH)ads and Au can be active sites and they cooperatively facilitate the thermodynamically and kinetically feasible formation of glyceric acid thus explaining the experimentally observed high activity and selectivity. Under acidic conditions, hydroxide coverage is negligible and the dihydroxyacetone emerges as the favored product. Calculations predict slow reaction kinetics, however, which explains the low activity and selectivity toward dihydroxyacetone reported in experiments. Overall, our findings highlight that computational studies should explicitly account for pH and coverage effects under alkaline conditions for electrocatalytic oxidation reactions to reliably predict electrocatalytic behavior. peerReviewed

An electrocatalyst for water splitting based on earth-abundant metals is reported. This perovskite–oxide catalyst, CaSrFe0.75Co0.75Mn0.5O6−δ (CSFCM), is examined using both experimental and computa...

RuO2 is one of the most important electrocatalyst materials as a key component of dimensionally stable anode (DSA) for chlorine evolution reaction, because of the high catalytic activity, while ano...

Systematic structure–activity correlations in the electrochemical surface science of CO₂ reduction (CO₂R) are typically anchored on low Miller-index (hkl) surfaces with characterization directed at the dominant well-defined basal planes. The present investigation focused on the visualization of the step edges of unreconstructed Cu(100), with and without CO dissolved in 0.1 M KOH, at the early onset-potential region of CO₂R. Operando electrochemical scanning tunneling microscopy revealed that the step-edge direction changed dramatically upon the adsorption–desorption of CO at potentials of −1.0 to −0.8 V. Quantum mechanical calculations corroborated the favorable transformation of the step-edge direction from ⟨110⟩ to ⟨001⟩ as the pristine surface was decorated by CO.

The production of hydrogen via a proton-exchange membrane water electrolyzer (PEM-WE) is directly dependent on the rational design of electrocatalysts for the anodic oxygen evolution reaction (OER), which is the bottleneck of the process. Here, we present a smart design strategy for enhancing Ir utilization and stabilization. We showcase it on a catalyst, where Ir nanoparticles are efficiently anchored on a conductive support titanium oxynitride (TiON x ) dispersed over carbon-based Ketjen Black and covered by a thin layer of copper (Ir/CuTiON x /C), which gets removed in the preconditioning step. Electrochemical OER activity, stability, and structural changes were compared to the Ir-based catalyst, where Ir nanoparticles without Cu are deposited on the same support (Ir/TiON x /C). To study the effect of the sacrificial less-noble metal layer on the catalytic performance of the synthesized material, characterization methods, namely X-ray powder diffraction, X-ray photoemission spectroscopy, and identical location transmission electron microscopy were employed and complemented with scanning flow cell coupled to an inductively coupled plasma mass spectrometer, which allowed studying the online dissolution during the catalytic reaction. Utilization of these advanced methods revealed that the sacrificial Cu layer positively affects both Ir OER mass activity and its durability, which was assessed via S-number, a recently reported stability metric. Improved activity of Cu analogue was ascribed to the higher surface area of smaller Ir nanoparticles, which are better stabilized through a strong metal-support interaction (SMSI) effect.

The production of hydrogen via water electrolysis using renewable electricity is a promising carbon-neutral technology. In this contribution, we report insights into the hydrogen evolution reaction (HER) in H2SO4 on Pt(111) and graphene-covered Pt(111), in addition to the electrochemical properties of graphene overlayers. As-prepared graphene overlayers are selectively permeable to H+ ions in the electrolyte, allowing H+ ions into the confined layer between graphene and Pt(111) while excluding SO42- and other anions. We demonstrate that defects in these as-prepared graphene overlayers can be generated from oxidation at high overpotentials or reduction from the production of H-2 bubbles and postulate that HER occurs locally at only Pt(111) in the proximity of defects in graphene overlayers on asprepared G/Pt(111) electrodes, and as defects in graphene increases, more of the Pt(111) surface becomes utilized for HER. Kinetically, the addition of defective graphene overlayers can increase the geometric HER rate by up to 200%, while Tafel slopes and [H+] reaction orders remain unchanged. These results shed kinetic insight into the nature of graphene overlayers and their effect on HER catalysis and also demonstrate the promise of confinement modifications in designing catalysts with properties closer to achieving optimum rates.

The hydrogen evolution reaction (HER) has been crucial for the development of fundamental knowledge on electrocatalysis and electrochemistry, in general. In alkaline media, many key questions concerning pH-dependent structure–activity relations and the underlying activity descriptors remain unclear. While the presence of Ni(OH)2 deposited on Pt(111) has been shown to highly improve the rate of the HER through the electrode’s bifunctionality, no studies exist on how low coverages of Ni(OH)2 influence the electrocatalytic behavior of Cu surfaces, which is a low-cost alternative to Pt. Here, we demonstrate that Cu(111) modified with 0.1 and 0.2 monolayers (ML) of Ni(OH)2 exhibits an unusual non-linear activity trend with increasing coverage. By combining in situ structural investigations with studies on the interfacial water orientation using electrochemical scanning tunneling microscopy and laser-induced temperature jump experiments, we find a correlation between a particular threshold of surface roughness and the decrease in the ordering of the water network at the interface. The highly disordered water ad-layer close to the onset of the HER, which is only present for 0.2 ML of Ni(OH)2, facilitates the reorganization of the interfacial water molecules to accommodate for charge transfer, thus enhancing the rate of the reaction. These findings strongly suggest a general validity of the interfacial water reorganization as an activity descriptor for the HER in alkaline media. A.A. is a recipient of a doctorate (DOC) Fellowship of the Austrian Academy of Sciences at the Institute of Physical Chemistry. C.G. thanks the Austrian Research Promotion Agency (FFG) for funding via the project number 870523. J.K.-L. acknowledges funding by the Austrian Science Fund (FWF) via grant I-4114-N37. J.M.F. and V.C. acknowledge financial support from Ministerio de Ciencia e Innovación (project PID2019-105653GB-100) and Generalitat Valenciana (project PROMETEO/2020/063).

Author(s): Buckley, AK; Cheng, T; Oh, MH; Su, GM; Garrison, J; Utan, SW; Zhu, C; Toste, FD; Goddard, WA; Toma, FM | Abstract: We report the discovery of a quaternary ammonium surface additive for CO2 reduction on Ag surfaces that changes the Faradaic efficiency for CO from 25% on Ag foil to 97%, while increasing the current density for CO production by a factor of 9 from 0.14 to 1.21 mA/cm2 and reducing the current density for H2 production by a factor of 440 from 0.44 to 0.001 mA/cm2. Using ReaxFF reactive molecular dynamics, we find that the surface additive with the highest selectivity, dihexadecyldimethylammonium bromide, promotes substantial population of CO2 near the Ag surface along with sufficient H2O to activate the CO2. While a critical number of water molecules is required in the reduction of CO2 to CO, the trend in selectivity strongly correlates with the availability of CO2 molecules. We demonstrate that the ordering of the cationic modifiers plays a significant role around the active site, thus determining reaction selectivity. The dramatic improvement by addition of a simple surface additive suggests an additional strategy in electrocatalysis.

The spinel Co3O4 has emerged as a promising alternative to noble-metal-based electrocatalysts for electrochemical water electrolysis in alkaline medium. However, pure Co3O4, despite having high activity in anodic water oxidation, remains inactive toward the hydrogen evolution reaction (HER). Here, a Ni-doped Co3O4 (Co3-xNixO4) prepared by a simple method exhibits favorable HER activity and stability (>300 h, whether in 1 M KOH or the realistic 30 wt % KOH solution) after in situ electrochemical activation, outperforming almost all of the oxide-based electrocatalysts. More importantly, using the combination of in situ Raman spectroscopy and multiple high-resolution electron microscopy techniques, it is identified that the surface of Co3-xNixO4 crystals is reduced into intertwined CoyNi1-yO nanoparticles with highly exposed {110} reactive planes. Density functional theory calculations further prove that the Ni- doped CoO component in CoyNi1-yO plays a major role during the alkaline HER, because the introduction of Ni atoms into Co-O octahedra can optimize the electrical conductivity and tailor the adsorption/desorption free energies of H-ad and OHad intermediates.

The development of a bidirectional catalyst for oxygen reduction and water oxidation is the key to establishing sustainable energy transduction from renewable resources. We report a stable homogene...

The mass activity of a Pt-based catalyst can be sustained throughout the fuel cell vehicle life by optimizing its stability under the conditions of an oxygen reduction reaction (ORR) that drives th...

Discovering highly active and stable electrocatalysts for the oxygen evolution reaction (OER) is critical to the commercial development of many next-generation energy conversion and storage devices...

We have examined the temperature dependence of the activities for the oxygen reduction reaction (ORR) at Pt catalysts supported on Nb-doped SnO2 (Pt/Nb-SnO2) in 0.1 M HClO4. The apparent rate const...

Compound materials, such as transition-metal (TM) carbides, are anticipated to be effective electrocatalysts for the carbon dioxide reduction reaction (CO2RR) to useful chemicals. This expectation is nurtured by density functional theory (DFT) predictions of a break of key adsorption energy scaling relations that limit CO2RR at parent TMs. Here, we evaluate these prospects for hexagonal Mo2C in aqueous electrolytes in a multimethod experiment and theory approach. We find that surface oxide formation completely suppresses the CO2 activation. The oxides are stable down to potentials as low as −1.9 V versus the standard hydrogen electrode, and solely the hydrogen evolution reaction (HER) is found to be active. This generally points to the absolute imperative of recognizing the true interface establishing under operando conditions in computational screening of catalyst materials. When protected from ambient air and used in nonaqueous electrolyte, Mo2C indeed shows CO2RR activity.

Hydrogen evolution from a weak acid, acetic acid, occurs at extremely high rates for iron tetraphenylporphyrin in the presence tertiary amine as a cocatalyst. Kinetic analysis of H2 evolution for a...

It is highly desirable to develop all-pH-compatible hydrogen evolution reaction (HER) electrocatalysts that can be used universally in a variety of different electrolyzers and operated in different...

In this paper, an ingenious strategy was developed to construct a well-aligned nitrogen-doped carbon nanotube (NCNT) array electrode integrated with multiple electrocatalytically active components ...

Investigating the electrochemical reduction of aldehydes to alcohols provides insights into the mechanistic pathways of converting CO2 to alcohols electrochemically. In this work, both acetaldehyde...

Achieving an efficient and stable oxygen evolution reaction (OER) in an acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (...

Molecular first-row transition metal complexes for electrocatalytic CO2 reduction mostly feature N-donor supporting ligands, iron porphyrins being among the most prominent catalysts. Introducing N-...

The oxygen reduction reaction (ORR) is a key reaction in polymer electrolyte fuel cells and metal–air batteries. In these electrochemical systems, platinum group metals (PGMs) have been widely used as ORR electrocatalysts. Because of material cost and scarcity of platinum group metals, non-PGM electrocatalysts are considered to be an ideal alternative for mass production with low material cost. Many non-PGM electrocatalysts have been intensively studied such as pyrolyzed Fe-, N-doped carbon (Fe–N–C) catalysts. However, many non-PGM electrocatalysts including Fe–N–C still suffer from product selectivity due to the production of H2O2 as the byproduct. In this work, we synthesized an ORR electrocatalyst of Cu-, Fe-, and N-doped carbon nanotubes, (Cu,Fe)–N–CNT. This heterobimetallic catalyst showed the selective 4e– reduction of O2 to H2O with ca. 99%. Kinetic analysis of the electrocatalytic ORR and hydrogen peroxide reduction reaction (HPRR) in acidic media revealed that (Cu,Fe)–N–CNT showed two orders of magnitude higher rate constants for the direct 4e– reduction of O2 to H2O than those for the 2e– reduction of O2 to H2O2, whereas a monometallic Fe–N–CNT showed the same order of magnitude, indicating that the heterometallic cooperativity had a drastic impact on the ORR kinetics. Our findings would open up possibilities to develop non-PGM ORR electrocatalysts with heterobimetallic active sites for the selective ORR.

The complex α-[Fe(mcp)(OTf)2] (mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)-cyclohexane-1,2-diamine and OTf = trifluoromethanesulfonate anion) was reported in 2011 by some of us as an active water oxidation (WO) catalyst in the presence of sacrificial oxidants. However, because chemical oxidants are likely to take part in the reaction mechanism, mechanistic electrochemical studies are critical in establishing to what extent previous studies with sacrificial reagents have actually been meaningful. In this study, the complex α-[Fe(mcp)(OTf)2] and its analogues were investigated electrochemically under both acidic and neutral conditions. All the systems under investigation proved to be electrochemically active toward the WO reaction, with no major differences in activity despite the structural changes. Our findings show that WO-catalyzed by mcp–iron complexes proceeds via homogeneous species, whereas the analogous manganese complex forms a heterogeneous deposit on the electrode surface. Mechanistic studies show that the reaction proceeds with a different rate-determining step (rds) than what was previously proposed in the presence of chemical oxidants. Moreover, the different kinetic isotope effect (KIE) values obtained electrochemically at pH 7 (KIE ∼ 10) and at pH 1 (KIE = 1) show that the reaction conditions have a remarkable effect on the rds and on the mechanism. We suggest a proton-coupled electron transfer (PCET) as the rds under neutral conditions, whereas at pH 1 the rds is most likely an electron transfer (ET) NWO Echo grant 717.014.008. PGC2018-101737-B-I00 and 2017 SGR 00264 grants

Transition-metal- and nitrogen-codoped carbide-derived carbon/carbon nanotube composites (M-N-CDC/CNT) have been prepared, characterized, and used as cathode catalysts in anion-exchange membrane fuel cells (AEMFCs). As transition metals, cobalt, iron, and a combination of both have been investigated. Metal and nitrogen are doped through a simple high-temperature pyrolysis technique with 1,10-phenanthroline as the N precursor. The physicochemical characterization shows the success of metal and nitrogen doping as well as very similar morphologies and textural properties of all three composite materials. The initial assessment of the oxygen reduction reaction (ORR) activity, employing the rotating ring–disk electrode method, indicates that the M-N-CDC/CNT catalysts exhibit a very good electrocatalytic performance in alkaline media. We find that the formation of HO2– species in the ORR catalysts depends on the specific metal composition (Co, Fe, or CoFe). All three materials show excellent stability with a negligible decline in their performance after 10000 consecutive potential cycles. The very good performance of the M-N-CDC/CNT catalyst materials is attributed to the presence of M-Nx and pyridinic-N moieties as well as both micro- and mesoporous structures. Finally, the catalysts exhibit excellent performance in in situ tests in H2/O2 AEMFCs, with the CoFe-N-CDC/CNT reaching a current density close to 500 mA cm–2 at 0.75 V and a peak power density (Pmax) exceeding 1 W cm–2. Additional tests show that Pmax reaches 0.8 W cm–2 in an H2/CO2-free air system and that the CoFe-N-CDC/CNT material exhibits good stability under both AEMFC operating conditions.

Taking 50 years of effort, ambient pressure X-ray photoelectron spectroscopy (APXPS) has become a useful characterization tool for studies in heterogeneous catalysis and electrocatalysis. This achievement is realized not by mere improvement of instrumentation but through interactions between the desire to explore new scientific phenomena and the advancement of new techniques. Here we review a brief history of APXPS development and its applications in catalysis and electrocatalysis. With the selected recent case stories, we would like to illustrate the intertwining between tool driven and science driven breakthroughs. Looking forward from here, we also discuss new demands and current frontiers of APXPS investigations. It is a dynamic environment that we need for understanding real behavior of catalyst under varying conditions and of electrocatalysts with on-demand energy. Therefore, a precise control of reaction condition and efficient detection with improved spatial and temporal resolution are essential. Finally, designing reactors that are customized or dedicated for a given study is among future development of the field.

Cu electrodes are promising materials to catalyze the conversion of CO2 and CO into renewable fuels and valuable chemicals. However, a detailed description of the properties of the Cu–electrolyte i...

Electrocatalysis has been the cornerstone for enhancing energy efficiency, minimizing environmental impacts and carbon emissions, and enabling a more sustainable way of meeting global energy needs....

Herein, we report a [Re(bipyridine)]-carbon hybrid material for efficient and selective CO2 to CO conversion in water. The Re catalyst was incorporated into a nanoporous colloid-imprinted carbon (C...

The electrochemical CO2 reduction reaction (CO2RR) on Pd-based electrodes to dissolved formate and/or gaseous CO is largely dependent on potential and the electrode material, yet there is a lack of...

A facile non-template-assisted mechanical ball milling technique was employed to generate a PdBi alloy catalyst. The induced lattice strain upon the milling time caused a shift of the d-band center...

Electrocatalysts for CO2 reduction based on first-row transition metal ions have attracted attention as abundant and affordable candidates for energy conversion applications. Yet very few molecular iron electrocatalysts exhibit high selectivity for CO. Iron complexes supported by a redox-active 2,2′:6′,2″-terpyridine (tpy) ligand and a strong trans effect pyridyl-N-heterocyclic carbene ligand (1-methyl-benzimidazol-2-ylidene-3-(2-pyridine)) were synthesized and found to catalyze the selective electroreduction of CO2 to CO at very low overpotentials. Mechanistic studies using electrochemical and computational methods provided insights into the nature of catalytic intermediates that guided the development of continuous CO2 flow conditions that improved the performance, producing CO with >95% Faradaic efficiency at an overpotential of only 150 mV. The studies reveal general design principles for nonheme iron electrocatalysts, including the importance of lability and geometric isomerization, that can serve to guide future developments in the design of affordable and efficient catalysts for CO2 electroreduction.

The role of catalysts in aprotic Li–O2 batteries remains unclear. To identify the exact catalytic nature of oxide catalysts, a precisely surface-engineered model catalyst, perovskite (LaMnO3), was ...

The application of Pt alloy catalysts for oxygen reduction reactions (ORRs) in proton-exchange membrane fuel cells is severely impeded by base metal leaching, since the produced metal ions can resu...

Here, we have developed a dissolved oxygen and galvanic corrosion method to synthesize vertically aligned fluoride-incorporated nickel–iron oxyhydroxide nanosheet arrays on a compressed Ni foam as ...

Due to the scarcity and high cost of precious metals, the hydrogen economy would ultimately rely on non-platinum-group-metal (non-PGM) catalysts. The non-PGM-catalyzed oxygen reduction reaction, wh...

Direct activation of O–H bond in water via hydrogen atom transfer (HAT) reactions is a challenge because of its high bond dissociation energy. In this work, a strong hydrogen atom abstracting reage...

Developing active, durable, and inexpensive electrocatalysts is critical for hydrogen production to meet ever-growing sustainable energy needs. Nickel sulfides offer significant potential as electr...

Although electrochemical hydrogen evolution and oxidation are arguably the best-understood reactions in electrocatalysis, the anomalous effect of pH on hydrogen reaction kinetics has defied simple ...

Platinum group metal-free (PGM-free) materials based on pyrolyzed M–N–C precursors offer a promising approach to replacing rare and expensive platinum group metal-based oxygen reduction reaction (O...

Catalytic reduction of nitrite by an iron complex in water near neutral pH to form hydroxylamine and ammonium is reported. The catalyst is an iron center coordinated by the pentadentate macrocycle ...