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Here, we report a facile approach for synthesizing M–N–C catalysts (M = Co, Fe, Ni) at a commercial scale without employing organic solvents. Our characterization efforts indicate that single atomic catalysts with high surface areas were successfully obtained. Electrochemical measurements demonstrate that, among the three synthesized catalysts, Ni–N–C exhibits the highest performance in the electrochemical CO2 reduction reaction (CO2RR) to carbon monoxide (CO), affording 80% Faradaic efficiency (FE) of CO production at –0.49 VRHE with a turnover frequency (TOF) of 57,379 h–1. Large-scale synthesis coupled with high performance allows moving forward with the practical implementation of M–N–C catalysts for industrially relevant CO2RR.

This manuscript reports the electrosynthesis of ammonia from nitrate catalysed Cu derived from Cu2O materials. Cu2O (111) and (100) preferential grain orientations were prepared through electrodeposition. Cu derived from Cu2O (111) is more active and selective for ammonia formation than Cu2O (100) derived Cu. The highest faradaic efficiency (FE) was achieved for both catalysts at −0.3 V vs RHE, with Cu derived from Cu2O (111) reaching up to 80 %. Additional measurements with quasi-in situ X-ray photoelectron spectroscopy and in situ Raman spectroscopy revealed that Cu0 is the active phase during the reaction. The stability of the catalysts was examined by ex situ methods such as SEM, XRD and ICP elemental analysis. The catalysts underwent severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After 3 hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The FE after 3 hours remained higher for the Cu derived from Cu2O (111), suggesting that the activity is dependent on the initial structure and the different rates of dissolution and re-deposition.

This manuscript reports the electrosynthesis of ammonia from nitrate catalysed by Cu2O. Cu2O (111) and (100) preferential orientations were prepared through electrodeposition to investigate the effect of surface structure. Cu2O (111) is more active and selective for ammonia formation than Cu2O (100). The highest faradaic efficiency (FE) was achieved for both catalysts at -0.3 V vs RHE, with Cu2O (111) reaching up to 80%. Additional measurements with quasi-in situ X-ray photoelectron spectroscopy and in-situ Raman spectroscopy revealed that Cu0 is the active phase during the reaction. The stability of the catalysts was examined by ex-situ methods such as scanning electron microscopy, X-ray diffraction and inductively coupled plasma-optical emission spectrometry. The catalysts undergo severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After three hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The final FE was still higher for the original Cu2O (111) electrode.

This manuscript reports the simultaneous electrodeposition of Cu and Rh from an aqueous nitrate solution. The early stages of nucleation and growth of the bimetallic layer were explored using techniques such as cyclic voltammetry and current transients. Non-dimensional Scharifker-Hills graphs showed the occurrence of diffusion-controlled three-dimensional nucleation and growth best described by the Volmer-Weber mechanism. Additionally, different ratios of Cu−Rh electrodes were synthesized by varying the potential of deposition and the Rh content in the deposition bath. Characterization techniques including electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were employed to investigate the chemical composition and structure of the deposits. The results showed a higher amount of Cu2+ species in the layer than Cu+/Cu0 when a more negative potential was applied, and when Rh was present in high amounts in the deposition bath. The final morphology of the obtained material proved to be dependent on the deposition potentials and the Cu : Rh content, showing interdependency between the metals.

A facile and universal route for synthesizing transition metal borides has been developed by reaction of boron triiodide (BI3) with elemental transition metals. This method employs relatively low synthesis temperatures to afford single-phase samples of various binary and ternary metal borides, such as Fe2B, Co2B, Ni3B, TiB2, VB2, CrB2, and Ni2CoB. This synthesis protocol can be utilized for the topotactic transformation of metal shapes into their respective borides, as exemplified by transformation of Ni foam to Ni3B foam. In situ powder X-ray diffraction studies of the Ni-BI3 system showed that the crystalline nickel borides, Ni4B3 and Ni2B, start to form at temperatures as low as 700 K and 877 K, respectively, which is significantly lower than the typical synthesis temperatures required to produce these borides. Ni3B synthesized by this method was tested as a supporting material for oxygen evolution reaction (OER) in acidic media. Composite electrocatalysts of IrO2/Ni3B with only 50% of IrO2 exhibit current densities and stability similar to pure IrO2 at mass loadings lower than 0.5 mg cm−2, indicating Ni3B could be a promising supporting material for acidic OER.

Many industrial chemical processes involve a high-energy demand (often still derived from fossil fuels), toxic reactants, and the production of high amounts of waste. A good example is the production of ammonia and urea via the Haber-Bosh and Bosch-Meiser processes, respectively. These two nitrogen-containing compounds are mostly used in the fertilizer industry and with the increase in the world population, their production is expected to increase. Additionally, NH3 itself is responsible for 2% of the annual world energy consumption and has a carbon footprint of 1.5 tons of CO2 per ton of NH3 [1]. Therefore, the development of more efficient, less hazardous technologies that are based on renewable energies to produce valuable N- containing compounds, has become one of the most challenging topics for chemical synthesis. By using electrochemical methods for the synthesis of ammonia and urea, toxic and dangerous chemicals can be replaced with clean electrons. Furthermore, the efficiency and selectivity of the reactions can be tuned by the applied potential, and more importantly, the energy used can come from renewable sources like wind or solar [2]. In this talk, I will show the recent advances from our group in the development of catalysts for the electrocatalytic synthesis of ammonia and urea (as for example Cu2O and CuRh) and the reaction mechanism when using nitrate as a substrate [3]. References: [1] S. Giddey, et al, Int. J. Hydrogen Energy, 38 (2013) 14576–14594 [2] Frontana-Uribe, B. A. et al; Green Chem. 2010, 12 (12) 2099– 2119 [3] D. Anastasiadou, Y. van Beek, M. C. Figueiredo, in preparation. Figure 1: SEM images of two electrodeposited electrocatalysts used for ammonia and urea electrosynthesis from nitrates: a) CuRh and b) CuO. Figure 1

Electrochemistry-based processes to produce ammonia have recently gained widespread interest by the scientific community because they provide a way to reduce the high carbon emissions currently associated with ammonia production. Global NH3 demand is expected to rise since it is included in various energy scenarios as a possible green transportation fuel and storage medium of renewable electricity involving fuel cells.1 Several electrochemical and hybrid electrochemical processes with plasma integration are currently being investigated to produce NH3 via different nitrogen sources, such as N2, NO3 -/NO2 - or NO. The utilization of NO3 - from wastewater sources can be valuable for the environmental and health issues associated with NO3 - contamination. Additionally, NO3 - electroreduction in aqueous media is an attractive approach to investigate the catalysis due to its high solubility and the low dissociation energy needed to break the N=O bond. Cu and Cu-based materials have extensively been studied for NH3 production through NO3 - electroreduction. Earlier studies on Cu single crystals2 in alkaline media showed that Cu (100) performs better than Cu (111) in reducing the NO2 - intermediate to hydroxylamine, which is believed to be the precursor to NH3. On the contrary, recent density functional theory calculations3 showed that a Cu−Cu couple with 2.57 Å distance serves as a catalytic center, leading to the conclusion that Cu (111) is the most active surface termination. In this work, preferentially oriented Cu2O crystals with (111), (100), and (110) terminations were obtained via electrodeposition and evaluated for their performance in NO3 - electroreduction to NH3 (Figure 1). To understand which oxidation state of Cu represents the active phase, the samples were investigated by in-situ Raman spectroscopy. According to a recent study, the active phase was a combination of Cu and Cu+.4 Our results point to the immediate reduction of remaining Cu+ species during application of -0.3V vs. Ag/AgCl and formation of Cu(OH)2 at more negative potentials. The presence of Cu(OH)2 was also apparent from ex-situ XPS and UV-Vis analysis. Moreover, post-reaction XRD analysis showed a retainment of the crystal orientation on the reduced Cu surfaces. All the nanostructured catalysts were active for NO3 - reduction and produced NH3 with faradaic efficiencies above 40%. Cu2O (111) was the most efficient for NH3 synthesis reaching a faradaic efficiency of up to 99%. 1 D. Anastasiadou, Electrochem. Sci. Adv.,submitted. 2 E. Pérez-Gallent, Electrochim. Acta, 2017, 227, 77–84. 3 T. Hu, ACS Catal., 2021, 11, 14417–14427. 4 Y. Wang, Angew. Chemie Int. Ed., 2020, 59, 5350–5354. Figure 1

The adsorption and reactivity of acetonitrile (CH3CN) have been studied on Pt(111) and Pt(100) electrodes in 0.1 M HClO4 and 0.1 M NaOH solutions with CH3CN concentrations ranging from 10–3 to 1 M. Cyclic voltammetry results show that these processes are structure sensitive and that the hydrogen adsorption/desorption region is partially blocked on Pt(111) in acidic solutions while the inhibition is almost complete on Pt(100) in both acidic and alkaline media. However, for Pt(111), hydrogen adsorption is practically unaltered in the 0.1 M NaOH electrolyte. In situ infrared measurements and density functional theory calculations suggest that rehybridized adsorbed acetonitrile reacts with adsorbed hydroxyl species at high potentials forming a hydroxylated adsorbed species. The latter is bonded to the Pt surface by electrodonation and can be reduced to an intermediate in which the double C–N bond is tilted with respect to the metal surface. Lastly, oxygen reduction reaction (ORR) has been investigated by using the hanging meniscus rotating disk electrode configuration. Limiting current densities decrease more drastically for Pt(100) than for Pt(111) as acetonitrile concentration is increased because of the higher acetonitrile coverage for the former one. The onset potential for ORR is shifted to less positive values in acidic media because of a blocking effect of acetonitrile. In alkaline media, the onset potential for Pt(111) is slightly more positive for low concentrations of acetonitrile because oxide formation, which hinders oxygen reduction for the more positive potentials, is inhibited due to the presence of adsorbed acetonitrile species at low coverages. This work has been financially supported by MCINN-FEDER (Spain) through project CTQ2016-76221-P. V.B.-M. thankfully acknowledges MINECO, the award of a predoctoral grant (BES-2014-068176, project CTQ2013-44803-P) and a student stay grant (EEBB-I-16-11656).

Nanoparticle modified electrodes constitute an attractive way to tailor-make efficient carbon dioxide (CO2) reduction catalysts. However, the restructuring and sintering processes of nanoparticles under electrochemical reaction conditions not only impedes the widespread application of nanoparticle catalysts, but also misleads the interpretation of the selectivity of the nanocatalysts. Here, we colloidally synthesized metallic copper (Cu) and silver (Ag) nanoparticles with a narrow size distribution (10%) and utilized them in electrochemical CO2 reduction reactions. Monometallic Cu and Ag nanoparticle electrodes showed severe nanoparticle sintering already at low overpotential of -0.8 V vs. RHE, as evidenced by ex situ SEM investigations, and potential-dependent variations in product selectivity that resemble bulk Cu (14% for ethylene at -1.3 V vs. RHE) and Ag (69% for carbon monoxide at -1.0 V vs. RHE). However, by co-deposition of Cu and Ag nanoparticles, a nanoparticle stabilization effect was observed between Cu and Ag, and the sintering process was greatly suppressed at CO2 reducing potentials (-0.8 V vs. RHE). Furthermore, by varying the Cu/Ag nanoparticle ratio, the CO2 reduction reaction (CO2RR) selectivity towards methane (maximum of 20.6% for dense Cu2.5-Ag1 electrodes) and C2 products (maximum of 15.7% for dense Cu1-Ag1 electrodes) can be tuned, which is attributed to a synergistic effect between neighbouring Ag and Cu nanoparticles. We attribute the stabilization of the nanoparticles to the positive enthalpies of Cu-Ag solid solutions, which prevents the dissolution-redeposition induced particle growth under CO2RR conditions. The observed nanoparticle stabilization effect enables the design and fabrication of active CO2 reduction nanocatalysts with high durability.

The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.

The first part of this communication studies the electrochemical properties of thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) grown on the three basal plane platinum electrodes via cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy and in situ FTIR spectroelectrochemistry. In the second part of this work the redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at these platinum modified electrodes is investigated via cyclic voltammetry and electrochemical impedance spectroscopy in order to elucidate the effect of some polymer properties on its electrocatalytic behavior, such as the ionic resistance, nature of the doping ion and the structure. First of all, it was found that the ionic resistance of the PEDOT films electrochemically synthesized on platinum electrodes increases in the order Pt(100) < Pt(110) < Pt(111) and the advantages of using single crystal platinum electrodes coated with PEDOT for the IR study of individual mobile species flux and the evolution of charge carriers during the reduction process of p-doped PEDOT were proven. On the other hand, it was found that compact, rigid and low resistance PEDOT films show higher standard charge transfer rates for the DMcT redox reaction than those that have a more porous structure and higher ionic resistance. Finally, PEDOT films doped with alkaline ions are more electrocatalytic for the oxidation process of the protonated form of DMcT.