Aqueous CO2 Research Articles

Templating Bicarbonate in the Second Coordination Sphere Enhances Electrochemical CO2 Reduction Catalyzed by Iron Porphyrins.

Bicarbonate-based electrolytes are ubiquitous in aqueous electrochemical CO2 reduction, particularly in heterogenous catalysis, where they demonstrate improved catalytic performance relative to other buffers. In contrast, the presence of bicarbonate in organic electrolytes and its roles in homogeneous electrocatalysis remain underexplored. Here, we investigate the influence of bicarbonate on iron porphyrin-catalyzed electrochemical CO2 reduction. We show that bicarbonate is a viable proton donor in organic electrolyte (pKa = 20.8 in dimethyl sulfoxide) and that urea pendants in the second coordination sphere can be used to template bicarbonate in the vicinity of a molecular iron porphyrin catalyst. The templated binding of bicarbonate increases its acidity, resulting in a 1500-fold enhancement in catalytic rates relative to unmodified parent iron porphyrin. This work emphasizes the importance of bicarbonate speciation in wet organic electrolytes and establishes second-sphere bicarbonate templating as a design strategy to harness this adventitious acid and enhance CO2 reduction catalysis.

AI models for correlation of physical properties in system of 1DMA2P‐CO2‐H2O

AbstractIn this work, the density, viscosity, and specific heat capacity of pure 1‐dimethylamino‐2‐propanol (1DMA2P) as well as aqueous unloaded and CO2‐loaded 1DMA2P solution (with a CO2 loading of 0.04–0.70 mol CO2/mol amine) were measured over the 1DMA2P concentration range of 0.5–3.0 mol/L and temperature range of 293–323 K. The observed experimental results of these thermophysical properties of the 1DMA2P‐H2O‐CO2 system were correlated using empirical models as well as artificial neural network (ANN) models (namely, back‐propagation neural network [BPNN] and radial basis function neural network [RBFNN] models). It was found that the developed BPNN and RBFNN models could predict the experimental results of 1DMA2P‐H2O‐CO2 better than correlations using empirical models. The results could be treated as one of the accurate and potential methods to predict the physical properties for aqueous amine CO2 absorption systems.

Effect of methanol as an amphiphile on water structuring around a hydrate forming gas molecule: Insights from molecular dynamics simulations

Gas hydrates (GH) are crystalline compounds composed of small hydrophobic molecules encapsulated within cavities formed by hydrogen bonded water molecules. These compounds are an important source of fuel and are of application in gas storage and transportation. Processes such as nucleation, crystal growth, stability and decomposition of GH are controlled by the introduction of molecules referred to as additives. A challenging aspect in the study of GH is to explain at a molecular level the influence of additives on these processes. An intriguing case of additives is that of amphiphilic molecules which influence hydrate processes through their complex effects on the organization of water as well as on gas solubility. In this study, we apply molecular dynamics simulations to examine the effect of CH3OH, the simplest amphiphile and the most commonly used additive, on the organization of H2O molecules in the hydration shell of CO2, a hydrate forming gas. The interface between methanol–water liquid mixture and CO2 is examined by applying the Identification of Truly Interfacial Molecules (ITIM) technique, thereby minimizing the errors due to molecular level roughness at the interface. The organizational order of hydration shell water (HSW) is examined by evaluating the F4 order parameter. The results show that the presence of CH3OH enhances the availability of aqueous CO2 near the interface which makes the arrangement of HSW in this region more hydrate-like, resulting in an increase in value of F4 on approaching the interface from the bulk. It is also observed that CH3OH molecules tend to orient their hydrophobic CH3 group towards aqueous CO2 thereby inducing hydrate-like ordering of water in the hydration shell. However, on approaching the liquid surface, hydrate-like organization of HSW is opposed by CH3OH molecules at the surface which, owing to their –OH group oriented towards the liquid phase, significantly influences water orientation near the interface and decreases the value of F4. The net outcome of these opposing effects of CH3OH on hydrate-like ordering of HSW is the observation of a maximum in the value of F4 order parameter at a distance beneath the surface of the liquid and a progressive decrease from this maximum on moving further closer to the surface. The observed features of the value of F4 order parameter profile are explained based on the analysis of the intrinsic structure of the liquid–gas interface. The results indicate that, the presence of CH3OH leads to a region beneath the liquid surface where the extent of hydrate-like organization of HSW becomes maximum. However, CH3OH molecules significantly limits the availability of water molecules around aqueous gas, justifying the action of methanol as an inhibitor for hydrate formation when present at high concentrations. The results indicate that the effect of an amphiphile on GH formation is determined by its interaction with dissolved gas as well as by the influence of surface adsorbed amphiphile on water orientation and gas availability near the interface.

Frontispiece: Aqueous CO 2 Reduction on Si Photocathodes Functionalized by Cobalt Molecular Catalysts/Carbon Nanotubes

Photocatalytic CO2 Reduction Aqueous CO2 reduction on silicon photocathodes functionalized with cobalt molecular catalysts/carbon nanotubes is reported by Fei Li et al. in their Communication (e202201086).

Frontispiz: Aqueous CO2 Reduction on Si Photocathodes Functionalized by Cobalt Molecular Catalysts/Carbon Nanotubes

Photokatalytische CO2-Reduktion Die wässrige CO2-Reduktion an Silicium-Photokathoden, die mit molekularen Cobaltkatalysatoren und Kohlenstoffnanoröhren funktionalisiert sind, wird in der Zuschrift von Fei Li et al. vorgestellt (e202201086).

Impacts of oil components on the stability of aqueous bulk CO2 foams: An experimental study

Study of foam stability in the presence of oil components is mainly devoted to the impacts of aliphatic components like short- and long-chained alkanes. In this study, several experiments, including critical micelle concentration (CMC) determination, IFT measurement, high pressure bulk foam stability as well as foam texture visualization and analysis have been designed and performed in the presence of various oil solution samples to explore the impacts of aromatic components and compare them with the impacts of aliphatic components on CO2 foam stability. Alpha-Olefin-Sulfonate (AOS) surfactant solutions with different concentrations of surfactant in the presence of various synthetic oil solutions comprising toluene and n-heptane were prepared to compare the interfacial behavior and performance of the surfactant solutions containing aromatic and aliphatic components with regards to foam stability. The results revealed that, due to higher micellar solubilization of the n-heptane as the aliphatic component compared to toluene, surfactant surface activity would be more detrimentally impacted by the presence n-heptane. Employing electrical conductivity measurements, it was observed that the CMC of surfactant solutions with addition of 1 vol% of toluene and n-heptane to the surfactant solution, increased by 15 and 19 times, respectively. Increase in surfactant concentration in solutions above CMC with no oil compound, did not show any promising improvement on foam stability. However, in the presence of different oil additives, increase in surfactant concentration from 0.1 wt% to 0.5 wt% resulted in the increase in foam stability by 45% on average measured by foam half-life time where the foam was generated by aeration method. This observation was further validated by the decrease in IFT, measured by spinning drop method, from the average range of 1.4 mN/m for different oil solutions to 0.6 mN/m by increasing surfactant concentration from 0.1 wt% to 0.5 wt%. IFT measurements between surfactant solutions and different oleic samples with oil components suggested that the presence of higher n-heptane in oil solutions resulted in higher IFT. Similar behavior was observed in foam stability measurements. Generally, addition of oil components to the foam solution resulted in lower foam stability. That is, higher oil content concentration would result in lower foam stability. Also, the presence of n-heptane had more detrimental impacts on foam stability compared to the presence of toluene. The texture of the resulted foam in the presence of toluene and n-heptane was visualized. It was observed that the texture of the foam generated in the presence of toluene had smaller bubble size compared to that in the presence of n-heptane. Also, it was observed that as time passes, oil droplets migrate from lamellae to the plateau borders, resulting in lamellae thinning and foam bubble coarsening and rupture.

Modeling dynamic viscosities of multi-component aqueous electrolyte solutions containing Li+, Na+, K+, Mg2+, Ca2+, Cl−, SO42− and dissolved CO2 under conditions of CO2 sequestration

Two accurate models were developed by this study for dynamic viscosities of multi-component aqueous electrolyte solutions containing Li+, Na+, K+, Mg2+, Ca2+, Cl−, SO42− and dissolved CO2 under conditions of CO2 sequestration. The first model is constructed by extending the Mao–Duan model for viscosities of binary aqueous solutions (aqueous single electrolyte solutions) of alkali-chloride to binary solutions of alkaline-earth chlorides, common sulfate and CO2 and combining it with Hu's mixing rule to model viscosities of multi-component solutions. The second model is constructed by improving the Goldsack–Franchetto model based on the Eyring's absolute rate theory to account for the effect of temperature on viscosity. The forms of both models are simple.Comparisons of calculations of the two models with experimental viscosity data show that both models can well represent dynamic viscosities of aqueous single electrolyte solutions and aqueous CO2 solutions at temperatures from 273 K to temperatures higher than 473 K, and at pressures from 0.1 MPa to 100 MPa. Furthermore, the two models can predict viscosities of aqueous NaCl solutions with dissolved CO2, brine containing Li+, Na+, K+, Mg2+, Ca2+, Cl−, SO42− and seawater over a wide P-T range. The absolute average deviations of the two models from most of experimental data sets are less than 2%.

Probing dissolved CO2(aq) in aqueous solutions for CO2 electroreduction and storage.

CO2 dissolved in aqueous solutions CO2(aq) is important to CO2 capture, storage, photo-/electroreduction in the fight against global warming and to CO2 analysis in drinks. Here, we developed microscale infrared (IR) spectroscopy for in situ dynamic quantitating CO2(aq). The quantized CO2(g) rotational state transitions were observed to quench for CO2(aq), accompanied by increased H2O IR absorption. An accurate CO2 molar extinction coefficient ε was derived for in situ CO2(aq) quantification up to 58 atm. We directly measured CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high-pressure conditions with high spectral and time resolutions. In KHCO3 electrolytes with CO2(aq) > ~1 M, CO2 electroreduction (CO2RR) to formate reached >98% Faradaic efficiencies on copper (Cu2O/Cu)–based electrocatalyst. Furthermore, CO2 dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO2(aq) supersaturation in aqueous systems, with implications to CO2 capture, storage, and supersaturation phenomena in natural water bodies.

Defect‐Assisted Electron Tunneling for Photoelectrochemical CO2 Reduction to Ethanol at Low Overpotentials

AbstractA Si/ZnO/Cu2O p‐n‐p heterojunction potential well with electron tunnels is fabricated for selective photoelectrochemical CO2 reduction to ethanol. This heterojunction is formed by growing n‐type ZnO nanosheets between defect‐rich p‐type Cu2O nanoparticles and nanoporous p‐type Si. Due to the existence of this potential well, the photogenerated electrons are trapped and accumulate inside n‐ZnO at low biases with the assistance of a ≈0.6 V built‐in potential, and escape into the Cu2O defect band. Under simulated sunlight, the Si/ZnO/Cu2O photocathode exhibits an onset potential of 0.2 V versus reversible hydrogen electrode (RHE) for aqueous photoelectrochemical CO2 reduction. Due to the confined electron energy in tunneling, the product selectivity is substantially tuned from CO or formate to ethanol, with an excellent Faradaic efficiency of ethanol over 60% at 0 V versus RHE.

Theoretical study of flue gas CO2 conversion to microalgae Chlorella vulgaris biomass in a bubble column photobioreactor: Tanks-in-series approach, kinetic modeling, and dynamic optimization

The current theoretical research is focused on using flue gas CO2 as carbon source to cultivate the microalgae Chlorella vulgaris in a bubble column photobioreactor. The tanks-in-series approach is used to model this semi-batch process. A kinetic model is deployed taking account of light irradiance as well as dissolved CO2 and inorganic nitrogen concentrations in the liquid phase. Model parameters are evaluated based on the experimental data reported in the literature. The developed model allows for detailed evaluation of concentration variations of key components along the photobioreactor over the whole process time. Using this method, variables can be distinguished and categorized into two groups: those with considerable spatial distributions and those that are assumed to be lumped and volume-averaged under certain conditions. Simulation results demonstrate a considerable aqueous CO2 concentration gradient along the photobioreactor for moderate liquid backflows unlike biomass and dissolved inorganic nitrogen. After performing sensitivity analysis, a multi-objective optimization problem is formulated and solved using parallelized differential evolution to enhance carbon capture rate and biomass productivity. The proposed approach for modeling and optimization improves the carbon capture rate with a reasonable biomass productivity. This method paves the way for developing more efficient and sophisticated bioprocess design procedures.

Chemical reactions of carbonate-rich mudstones with aqueous CO2 and their impacts on rock's local microstructural and chemo-mechanical properties

Assessment of the structural integrity of carbonate-rich rocks subjected to acidic brine strongly relies on the understanding of the coupling between the chemical changes and the alteration of the mechanical properties of rocks. This study aims at an integrated microscale chemo-mechanical and microstructural characterization of carbonate mudstones exposed to CO2-rich brine under high pressure and high temperature conditions. Digital image analysis was performed on X-ray micro-computed tomography (micro-CT) images to realize microstructural evolution and spatial distribution of pores and different material phases. This approach showed three distinct regions of porosity and carbonate content (resulting from dissolution and precipitation of calcium carbonates), which are critical for understanding the mechanical alteration of the rocks being investigated. Detailed analysis of the micro-CT images also revealed the preferred precipitation of calcium carbonates in pores parallel to the flow/reaction direction. Microscale chemo-mechanical testing performed using coupled grid nanoindentation and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) complemented the micro-CT results: dissolution zones close to the reacted surface were found to have lower hardness and indentation modulus while an increased values in adjacent precipitation zones was observed. Also, the thickness of the precipitation zones was found to be considerably higher in the direction of the bedding planes, which needs special attention in laminated rocks like shales and mudstones. The microstructural and mechanical properties of the microscale regions and the layered structure are expected to influence the overall mechanical properties and integrity of the rock. These results enhance our understanding of the microscale origin of the macroscopic mechanical alteration of carbonate-rich mudstones subjected to acidic brine.

Engineering of corrosion product-polymer hybrid layers for enhanced CO2 corrosion protection of carbon steel part two: Computational investigation and surface characterisation

Carbon dioxide internal corrosion of carbon steel pipelines remains a major issue that is typically mitigated via the addition of corrosion inhibitors. In specific operational environments, a protective natural corrosion product layer known as iron carbonate (FeCO 3 ) can evolve on internal pipeline walls, providing comparable corrosion inhibitionefficiency to that achieved from surfactants. However, in some instances, incomplete corrosion product coverage can initiate localised corrosion. In our previous work, we demonstrated the ability of Poly (allylamine hydrochloride) (PAH) to act synergistically with FeCO 3 when the corrosion product exhibits partial coverage of ×65 carbon steel surfaces in an aqueous CO 2 corrosion environment. In this work, we employ density functional theory (DFT) to show that PAH is able to coordinate with both FeCO 3 and the bare carbon steel surface, producing a FeCO 3 -PAH hybrid structure. The surface and chemical properties of a naturally formed FeCO 3 and the FeCO 3 -PAH hybrid layers are characterised employing scanning electron microscopy (SEM) coupled with focused ionic beam (FIB), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS). • The PAH molecules adsorb onto the carbon steel surface and corrosion product (FeCO 3 ) via chemisorption and physisorption. • The PAH molecules interact with FeCO 3 through coordination and hydrogen bonding producing a hybrid layer. • The PAH centres of interaction with film-free carbon steel and FeCO 3 film are protonated and neutral amine groups. • The crystal structure and layer thickness of FeCO 3 and FeCO 3 -PAH hybrid layers are characterised and compared.

On the Existence and Role of Formaldehyde During Aqueous Electrochemical Reduction of Carbon Monoxide to Methanol by Cobalt Phthalocyanine.

A long-time challenge in aqueous CO2 electrochemical reduction is to catalyze the formation of products beyond carbon monoxide with selectivity. Formaldehyde is the simplest of these products and one of the most relevant due to its broad use in the industry. Paradoxically it is one of the less reported product. Such scarcity may be in part explained by difficult identification and quantification using conventional chromatography or proton nuclear magnetic resonance techniques. Likewise, indirect detection methods are usually not compatible with labelled studies for asserting product origin. Recently, the possible production of formaldehyde during electrochemical reduction of carbon monoxide to methanol at cobalt phthalocyanine molecular catalyst in basic media has been the object of contradictory reports. By applying an analytical procedure based on proton NMR along with labelled studies, we provide definitive evidence for HCHO formation. We have further identified the possible scenarios for methanol formation through formaldehyde and revealed that the formation of the intermediate and its subsequent reduction are taking place at the same single active site. These studies open a new perspective to improve selectivity toward formaldehyde formation and to develop a subsequent chemistry based on reacting it with nucleophiles.

Aqueous CO2 Reduction on Si Photocathodes Functionalized by Cobalt Molecular Catalysts/Carbon Nanotubes

AbstractPhotoelectrochemical reduction of CO2 is a promising approach for renewable fuel production. We herein report a novel strategy for preparation of hybrid photocathodes by immobilizing molecular cobalt catalysts on TiO2‐protected n+‐p Si electrodes (Si|TiO2) coated with multiwalled carbon nanotubes (CNTs) by π–π stacking. Upon loading a composite of CoII(BrqPy) (BrqPy=4′,4′′‐bis(4‐bromophenyl)‐2,2′ : 6′,2′′ : 6′′,2′′′‐quaterpyridine) catalyst and CNT on Si|TiO2, a stable 1‐Sun photocurrent density of −1.5 mA cm−2 was sustained over 2 h in a neutral aqueous solution with unity Faradaic efficiency and selectivity for CO production at a bias of zero overpotential (−0.11 V vs. RHE), associated with a turnover frequency (TOFCO) of 2.7 s−1. Extending the photoelectrocatalysis to 10 h, a remarkable turnover number (TONCO) of 57000 was obtained. The high performance shown here is substantially improved from the previously reported photocathodes relying on covalently anchored catalysts.

Aqueous CO2 Reduction on Si Photocathodes Functionalized by Cobalt Molecular Catalysts/Carbon Nanotubes

Photoelectrochemical reduction of CO2 is a promising approach for renewable fuel production. We herein report a novel strategy for preparation of hybrid photocathodes by immobilizing molecular cobalt catalysts on TiO2 -protected n+ -p Si electrodes (Si|TiO2 ) coated with multiwalled carbon nanotubes (CNTs) by π-π stacking. Upon loading a composite of CoII (BrqPy) (BrqPy=4',4''-bis(4-bromophenyl)-2,2' : 6',2'' : 6'',2'''-quaterpyridine) catalyst and CNT on Si|TiO2 , a stable 1-Sun photocurrent density of -1.5 mA cm-2 was sustained over 2 h in a neutral aqueous solution with unity Faradaic efficiency and selectivity for CO production at a bias of zero overpotential (-0.11 V vs. RHE), associated with a turnover frequency (TOFCO ) of 2.7 s-1 . Extending the photoelectrocatalysis to 10 h, a remarkable turnover number (TONCO ) of 57000 was obtained. The high performance shown here is substantially improved from the previously reported photocathodes relying on covalently anchored catalysts.

Manganese Carbonyl Complexes as Selective Electrocatalysts for CO2 Reduction in Water and Organic Solvents

ConspectusThe electrochemical reduction of CO2 provides a way to sustainably generate carbon-based fuels and feedstocks. Molecular CO2 reduction electrocatalysts provide tunable reaction centers offering an approach to control the selectivity of catalysis. Manganese carbonyl complexes, based on [Mn(bpy)(CO)3Br] and its derivatives (bpy = 2,2′-bipyridine), are particularly interesting due to their ease of synthesis and the use of a first-row earth-abundant transition metal. [Mn(bpy)(CO)3Br] was first shown to be an active and selective catalyst for reducing CO2 to CO in organic solvents in 2011. Since then, manganese carbonyl catalysts have been widely studied with numerous reports of their use as electrocatalysts and photocatalysts and studies of their mechanism.This class of Mn catalysts only shows CO2 reduction activity with the addition of weak Brønsted acids. Perhaps surprisingly, early reports showed increased turnover frequencies as the acid strength is increased without a loss in selectivity toward CO evolution. It may have been expected that the competing hydrogen evolution reaction could have led to lower selectivity. Inspired by these works we began to explore if the catalyst would work in protic solvents, namely, water, and to explore the pH range over which it can operate. Here we describe the early studies from our laboratory that first demonstrated the use of manganese carbonyl complexes in water and then go on to discuss wider developments on the use of these catalysts in water, highlighting their potential as catalysts for use in aqueous CO2 electrolyzers.Key to the excellent selectivity of these catalysts in the presence of Brønsted acids is a proton-assisted CO2 binding mechanism, where for the acids widely studied, lower pKa values actually favor CO2 binding over Mn–H formation, a precursor to H2 evolution. Here we discuss the wider literature before focusing on our own contributions in validating this previously proposed mechanism through the use of vibrational sum frequency generation (VSFG) spectroelectrochemistry. This allowed us to study [Mn(bpy)(CO)3Br] while it is at, or near, the electrode surface, which provided a way to identify new catalytic intermediates and also confirm that proton-assisted CO2 binding operates in both the “dimer” and primary (via [Mn(bpy)(CO)3]−) pathways. Understanding the mechanism of how these highly selective catalysts operate is important as we propose that the Mn complexes will be valuable models to guide the development of new proton/acid tolerant CO2 reduction catalysts.

Photocatalytic Aqueous CO2 Reduction to CO and CH4 Sensitized by Ullazine Supramolecular Polymers.

There has been rapid progress on the chemistry of supramolecular scaffolds that harness sunlight for aqueous photocatalytic production of hydrogen. However, great efforts are still needed to develop similar photosynthetic systems for the great challenge of CO2 reduction especially if they avoid the use of nonabundant metals. This work investigates the synthesis of supramolecular polymers capable of sensitizing catalysts that require more negative potentials than proton reduction. The monomers are chromophore amphiphiles based on a diareno-fused ullazine core that undergo supramolecular polymerization in water to create entangled nanoscale fibers. Under 450 nm visible light these fibers sensitize a dinuclear cobalt catalyst for CO2 photoreduction to generate carbon monoxide and methane using a sacrificial electron donor. The supramolecular photocatalytic system can generate amounts of CH4 comparable to those obtained with a precious metal-based [Ru(phen)3](PF6)2 sensitizer and, in contrast to Ru-based catalysts, retains photocatalytic activity in all aqueous media over 6 days. The present study demonstrates the potential of tailored supramolecular polymers as renewable energy and sustainability materials.

Nitrogen-Doped Carbon Polyhedrons Confined Fe-P Nanocrystals as High-Efficiency Bifunctional Catalysts for Aqueous Zn-CO2 Batteries.

Emerging Fe bonded with heteroatom P in carbon matrix (FePC) holds great promise for electrochemical catalysis, but the design of highly active and cost-efficient FePC structure for the electrocatalytic CO2 reduction reaction (CO2 RR) and aqueous ZnCO2 batteries (ZCBs) is still challenging. Herein, polyhedron-shaped bifunctional electrocatalysts, FeP nanocrystals anchored in N-doped carbon polyhedrons (Fe-P@NCPs), toward a reversible aqueous ZnCO2 battery, are reported. The Fe-P@NCPs are synthesized through a facile strategy by using self-templated zeolitic imidazolate frameworks (ZIFs), followed by an in situ high-temperature calcination. The resultant catalysts exhibit aqueous CO2 RR activity with a CO Faradaic efficiency up to 95% at -0.55V versus reversible hydrogen electrode (RHE), comparable to the previously best-reported values of FeNC structure. The as-constructed ZCBs with designed Fe-P@NCPs cathode, show the peak power density of 0.85mW cm-2 and energy density of 231.8Wh kg-1 with a cycling durability over 500 cycles, and outstanding stability in terms of discharge voltage for 7 days. The high selectivity and efficiency of the battery are attributed to the presence of highly catalytic FeP nanocrystals in N-doped carbon matrix, which can effectively increase the number of catalytically active sites and interfacial charge-transfer conductivity, thereby improving the CO2 RR activity.

High-efficient carbon dioxide-to-formic acid conversion on bimetallic PbIn alloy catalysts with tuned composition and morphology

CO2 electroreduction to value-added chemicals and fuels has gained increasing attention; however, there are only a few catalysts with high performance under mild conditions that can be used in this technique. In this study, single metal Pb, In and bimetallic PbIn catalysts for aqueous CO2 electroreduction were prepared using a facile 3-step process including PbIn granulation by reducing Pb(NO3)2/In(NO3)3 aqueous solution with NaBH4, calcination in air, and in situ electroreduction. The bimetallic PbIn catalysts had better catalytic performance on CO2 electroreduction than single metal catalysts. The bimetallic Pb7In3 catalyst (atomic ratios of Pb and In is 7:3) presented the highest formic acid faradaic efficiency of 91.6% at −1.26 V vs reversible hydrogen electrode in a 0.5 M CO2-saturated KHCO3 aqueous solution, which was 13% and 9.7% higher than that of single Pb and In catalysts, respectively. Moreover, the catalyst remained active after 10 h of continuous CO2 electrolysis with a stale current density of −17 mA cm−2. The experimental results showed that the excellent catalytic performance of Pb7In3 catalyst may stem from its higher electrochemical active surface area, lower charge-transfer resistance and the synergistic effect of Pb and In in the catalyst. The presented bimetallic PbIn catalysts may have a wide of application prospect, and they may be synthesized from heavy metals in industrial wastewaters.

Electrocatalytic reduction of nitrate by in situ generated cobalt nanoparticles.

The cobalt pyridinophane complex [Co(HN4)Cl2]+ (HN4 = 3,7-diaza-1,5(2,6)-dipyridinacyclooctaphane) is converted under catalytic conditions to an electrode-adsorbed species. Aqueous Co2+ solutions similarly deposit a species under these conditions. Surface characterization reveals the formation of Co nanoparticles. These nanoparticles are active in the electrocatalytic redution of aqueous nitrate.