KHCO3 Aqueous Solution Research Articles

Free‐standing Stanene for High Selectivity of Formate in Electrocatalytic Carbon Dioxide Reduction Reaction

AbstractAs well‐known electrocatalysts with good catalytic efficiency for carbon dioxide reduction reaction (CO2RR) towards the production of formate, tin (Sn)‐based catalysts have aroused broad concern. Here, free‐standing porous stanene is synthesized for the first time by a facile wet chemical method, and its excellent electrocatalytic performance for formate (HCOO−) formation in CO2RR is demonstrated. High Faradaic efficiency (F.E., 93% at −930 mV versus reversible hydrogen electrode (RHE)) can be achieved in the CO2RR catalyzed by stanene in 0.5 m KHCO3 aqueous solution. The in situ Mössbauer spectra reveal that zero‐valent Sn aids in improving the selectivity of formate production. Furthermore, density functional theory calculations suggest that the high selectivity of HCOO− of CO2RR on stanene mainly originates from the edge sites on Sn (100). To further explore the practicability of the stanene‐based catalysts for CO2RR, stanene decorated by 3 wt% BP‐2000 is prepared, showing an excellent F.E. of 98% at −930 mV versus RHE due to the higher exposure of catalytic active sites. These new findings of the activity origination and reaction mechanism of stanene contribute to the deeper understanding of Sn‐based catalysts for CO2RR, which is beneficial for the future designation of highly efficient CO2RR catalysts.

Facile synthesis of Cu-Zn bimetallic metal-organic framework for effective catalyst toward electrochemical reduction of CO2

Bimetallic metal-organic framework (BM) and high temperature BM (HTBM) based catalysts have several advantages, including uniformly distributed bimetallic ions, less tendency towards aggregation, and more stable interfacial sites. In this study, CuZn-MOF were synthesized using ZIF-8 as a template, and then calcination at a high temperature in the nitrogen atmosphere. The electrochemical reduction CO2 (ERC) was taking place on an H-type cell in 0.1 M KHCO3 aqueous solution. The HTBM calcination at 700 °C exhibited excellent electrochemical CO2 reduction properties, including high CO selectivity (∼ 90%) and low overpotential (< −1.5 V)

Metal-organic framework-derived indium nanotubes for CO2 electroreduction to formate

Electrochemical conversion of CO2 to chemicals is an appealing route to reduce carbon emission and achieve carbon neutrality. Indium (In) is a promising electrocatalyst for CO2-to-formate conversion due to its high selectivity to formate, but is still hindered by low current density and poor stability. In this work, we propose the construction of In nanotubes from MIL-68(In) metal-organic framework nanotubes by a electrolytic route, which is simple, rapid and low-cost. Benefiting from the nanotube morphology and abundant unsaturated coordination In sites, the as-synthesized In nanotubes exhibit high performance for the electrochemical CO2-to-formate conversion. The formate Faradaic efficiency can reach 98.6% at −1.2 V versus reversible hydrogen electrode by using 0.5 M KHCO3 aqueous solution as electrolyte in H-cell, with current density of 24.8 mA cm−2.

Interface engineering of a GaN/In2O3 heterostructure for highly efficient electrocatalytic CO2 reduction to formate

Electrocatalytic CO2 reduction reaction (eCO2RR) to obtain formate is a promising method to consume CO2 and alleviate the energy crisis. Indium-based electrocatalysts have demonstrated considerable potential to produce formate. However, their unsatisfactory long-term stability and selectivity restrict their widespread application. In this study, a heterostructure of GaN- and In2O3-encapsulated porous carbon nanofibers was constructed via electrospinning and the phase transition of eutectic gallium-indium during calcination. The GaN and In2O3 nanoparticle-encapsulated porous carbon nanofibers, when used as electrocatalysts for eCO2RR, displayed high formate selectivity with a faradaic efficiency of 87% and maximum partial current density of 29.7 mA cm−2 in a 0.5 mol L−1 KHCO3 aqueous solution. The existence of the interface can cause a positive shift in the In 3d binding energy, leading to electronic redistribution. Moreover, the GaN component induced a higher proportion of O-vacancy sites in the In2O3 phase, resulting in improved selectivity for CO2-to-formate. In-situ Raman experiments and density functional theory calculations revealed that the interface between GaN and In2O3 could lower the adsorption energy of the key intermediates for formate production, thus providing superior eCO2RR performance. In addition, the framework of the porous carbon nanofibers exhibited a large electrochemically active surface area, which enabled the full exposure of the active sites. This study highlights the cooperation between GaN and In2O3 components and provides new insights into the rational design of catalysts with high CO2-to-formate conversion efficiencies.

Ultrathin ZnIn2S4 nanosheet arrays activated by nitrogen-doped carbon for electrocatalytic CO2 reduction reaction toward ethanol

Ternary ZnIn2S4 (ZIS) is a kind of potential electrocatalyst for CO2 reduction reaction (CO2RR). However, the reported reduction products are usual C1 species. Considering that N doped carbon can increase adsorption of CO2 molecules, facilitate electron transfer, and activate active sites, here ultrathin ZIS nanosheet arrays (ZIS NSAs) grown on N doped carbon cloth (NDCC) were synthesized through a facile hydrothermal route. The as-synthesized ZIS NSAs/NDCC enabled electrocatalytic CO2RR toward ethanol with the highest 42 % faradaic efficiency (FE) at an applied potential of − 0.7 V versus the reversible hydrogen electrode (RHE) in CO2-saturated 0.5 M KHCO3 aqueous solution. This is first report on ZIS-based electrocatalyst for electrocatalytic CO2RR toward ethanol production. The experimental results and density functional theory (DFT) calculations showed that NDCC could enhance the CO2RR activity and promote CO-CO coupling process. Our work not only provides a new electrocatalyst for CO2RR to ethanol but also stresses the influence of N doped carbon substrate and bimetallic effect on electrocatalytic CO2RR.

(Digital Presentation) Multi-Regression Analysis for Metal Sulfide-Based CO2 Reduction

The electrochemical reduction of carbon dioxide (CO2) is a promising approach towards the utilization of CO2 as a carbon feedstock, which is desirable for mitigating global warming and closing the carbon cycle. Despite the desire to develop metal-based electrocatalysts for CO2 reduction, CO2 reduction activity on metal electrodes is limited largely by the scaling relationship of intermediate binding energies. To fabricate efficient electrocatalysts, the adsorption energy of the target intermediate species in each reaction process should be optimized; however, such optimization becomes difficult when intermediate species have similar adsorption properties, resulting in an unavoidable overpotential. Multi-component compounds, such as metal sulfides, have the potential to break this scaling relationship because they possess multiple adsorption sites. Further, the investigation of electrochemical CO2 reduction activity on metal sulfides could provide insights into the origins of life, as metal sulfides have been hypothesized as proto-catalysts of extant CO2 reduction enzymes.Catalyst informatics is an effective approach for predicting the relationship between the physicochemical parameters and catalytic activity of materials. Here, we performed multi-regression analysis of electrochemical CO2 reduction catalyzed by metal sulfides to gain insight into the activity-determining properties of these electrocatalytic materials using following 14 physicochemical parameters as explanatory variables: metal-sulfur bonding length, nearest metal-metal distance, absolute negativity, standard redox potential of metals, band gap, first ionic energy, maximum radius of s-orbital, d-electron number, molar capacity of heat, formation enthalpy, metal-sulfur-metal angle, maximum radius of d-orbital, position of conduction band edge, and electron affinity. To avoid the effect of collinearity among explanatory variables, we applied partial least squares (PLS) analysis for the multi-regression process. PLS extracts the main components and uses the principal component as the explanatory variable. As the correlation between the main components is set to zero, collinearity can be avoided. Further, the number of main components can be controlled, allowing for regression to be performed with fewer samples. In addition, we applied the least absolute shrinkage and selection operator (LASSO) regression analysis.To obtain objective variable for regression analysis, the synthesized metal sulfides were subjected to electrochemical CO2 reduction. After applying an electrochemical potential of -1.2 V vs. SHE for 1 h, CO and HCOO- were obtained as CO2 reduction products for several of the metal sulfide samples. Among the 14 samples examined (Ag2S, CdS, CoS2, CuS, Fe3S4, In2S3, MnS, MoS2, NiS2, Ni3S2, SnS2, TiS2, WS2, and ZnS), CdS and Ag2S exhibited the highest CO production activity, with Faradaic efficiencies of 37.2% and 29.5%, respectively, in a 0.1 M KHCO3 aqueous solution, whereas CuS maximized formate (HCOO-) production, with a FE of 4.5%. PLS and Lasso analyses revealed that CO production was largely affected by the structural parameter of metal-sulfur bond length; however, HCOO- generation was influenced by the electronic parameters of the metal centers, particularly absolute electronegativity. These findings are distinct from those of metal electrodes, for which the generation of CO and HCOO- is predominantly influenced by electronic parameters, demonstrating that CO2 reduction on metal sulfides proceeds by a different mechanism compared to that of the corresponding metal electrodes. As demonstrated in the present study, changing the structural parameters, such as metal-sulfur bond length, alters the adsorption characteristics of the intermediate species to optimize the CO/HCOO- production activity. We anticipate that the key parameters identified through multi-regression analysis of metal sulfides will prompt further study of the factors influencing the specificity of these unique electrochemical CO2 reduction catalysts.

BiO 2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO 2 Reduction to Formate

BiO _2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO ₂ Reduction to Formate

A novel π-d conjugated cobalt tetraaza[14]annulene based atomically dispersed electrocatalyst for efficient CO2 reduction

Tetraaza[14]annulenes (TAA) are synthetic macrocycles which are analogue to porphyrins. However, there are almost no reports about the synthesis of polymers based on TAA and neither on their use as electrocatalysts. The study of new catalysts to promote an efficient electrochemical conversion of carbon dioxide to valuable chemicals is a promising approach to relieve the pressure of carbon emissions and realize the carbon cycle. Herein, we first report the synthesis of a novel tetraaza[14]annulene (TAA) based organic polymeric metal complex (PMC) by a non-template method. This PMC is used as ligand to construct a π-d conjugated cobalt coordination polymer (Poly-TAA-Co) with CoN4 structure which is supported on multi-wall carbon nanotubes (CNTs) to work as an atomically dispersed efficient electrocatalyst for the CO2 reduction reaction (CO2RR). The resulting catalyst (Poly-TAA-Co-CNT) exhibits excellent performance, with a 90% CO faradaic efficiency, a low overpotential (390 mV) and good stability in 0.5 M KHCO3 aqueous solution. Density functional theory calculations confirmed that the cobalt tetra[14]annulene is an excellent active site for electrocatalytic CO2RR. This work not only inspires the design of novel TAA based macromolecules, but also paves the way to the development and application of new molecular-based catalysts for electrocatalytic CO2RR.

Accelerating Pd Electrocatalysis for CO2-to-Formate Conversion across a Wide Potential Window by Optimized Incorporation of Cu.

Electrochemical reduction of carbon dioxide (CO2) to formate is a viable way to reduce CO2 emissions and realize a carbon-neutral energy cycle. Although Pd can convert CO2 to formate with a high Faradaic efficiency at minimal overpotentials, it suffers from a limited and narrow potential window. Alloying is an important strategy for the catalyst design and tuning the electronic structures. Here, we report a series of PdCu bimetallic alloy catalysts with tunable compositions based on dendritic architectures. Optimal introduction of Cu atoms into the Pd matrix facilitates formate production and suppresses CO generation. In 0.1 M KHCO3 aqueous solution, our best candidate, Pd82Cu18 catalyst, delivered a high formate Faradaic efficiency of 96.0% at -0.3 V versus RHE. More interestingly, the high selectivity (>90%) toward formate maintained an enlarged electrochemical potential window of 600 mV. The ensemble effect with electronic coupling between Pd and Cu upon alloying and its induced moderate surface O-containing configuration were found to enhance the formate formation and suppress CO poisoning during CO2 reduction.

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.

Maximizing Electroactive Sites in a Three‐Dimensional Covalent Organic Framework for Significantly Improved Carbon Dioxide Reduction Electrocatalysis

AbstractSynthesis of functional 3D COFs with irreversible bond is challenging. Herein, 3D imide‐bonded COFs were constructed via the imidization reaction between phthalocyanine‐based tetraanhydride and 1,3,5,7‐tetra(4‐aminophenyl)adamantine. These two 3D COFs are made up of interpenetratedptsnetworks according to powder X‐ray diffraction and gas adsorption analyses. CoPc‐PI‐COF‐3 doped with carbon black has been employed to fabricate the electrocatalytic cathode towards CO2reduction reaction within KHCO3aqueous solution, displaying the Faradaic efficiency of 88–96 % for the CO2‐to‐CO conversion at the voltage range of ca. −0.60 to −1.00 V (vs. RHE). In particular, the 3D porous structure of CoPc‐PI‐COF‐3 enables the active electrocatalytic centers occupying 32.7 % of total cobalt‐phthalocyanine subunits, thus giving a large current density (jCO) of −31.7 mA cm−2at −0.90 V. These two parameters are significantly improved than the excellent 2D COF analogue (CoPc‐PI‐COF‐1, 5.1 % and −21.2 mA cm−2).

Maximizing Electroactive Sites in a Three-Dimensional Covalent Organic Framework for Significantly Improved Carbon Dioxide Reduction Electrocatalysis.

Synthesis of functional 3D COFs with irreversible bond is challenging. Herein, 3D imide-bonded COFs were constructed via the imidization reaction between phthalocyanine-based tetraanhydride and 1,3,5,7-tetra(4-aminophenyl)adamantine. These two 3D COFs are made up of interpenetrated pts networks according to powder X-ray diffraction and gas adsorption analyses. CoPc-PI-COF-3 doped with carbon black has been employed to fabricate the electrocatalytic cathode towards CO2 reduction reaction within KHCO3 aqueous solution, displaying the Faradaic efficiency of 88-96 % for the CO2 -to-CO conversion at the voltage range of ca. -0.60 to -1.00 V (vs. RHE). In particular, the 3D porous structure of CoPc-PI-COF-3 enables the active electrocatalytic centers occupying 32.7 % of total cobalt-phthalocyanine subunits, thus giving a large current density (jCO ) of -31.7 mA cm-2 at -0.90 V. These two parameters are significantly improved than the excellent 2D COF analogue (CoPc-PI-COF-1, 5.1 % and -21.2 mA cm-2 ).

Phase‐Dependent Electrocatalytic CO2 Reduction on Pd3Bi Nanocrystals

AbstractAlloying is a general strategy for modulating the electronic structures of catalyst materials. Compared to more common solid–solution alloys, intermetallic alloys feature well‐defined atomic arrangements and provide the unique platform for studying the structure‐performance correlations. It is, unfortunately, synthetically challenging to prepare the nanostructures of intermetallic alloys for catalysis research. In this contribution, we prepare intermetallic Pd3Bi nanocrystals of a uniform size via a facile solvothermal method. These nanocrystals can phase‐transform into solid solution alloy via thermal annealing while retaining a similar composition and size. In 0.1 M KHCO3 aqueous solution, the intermetallic Pd3Bi can selectively reduce CO2 to formate with high selectivity (≈100 %) and stability even at &lt;‐0.35 V versus reversible hydrogen electrode, whereas the solid solution alloy has limited formate selectivity of &lt;60 %. Such unique phase‐dependence is understood via theoretical simulations showing that the crystallographic ordering of Pd and Bi atoms within intermetallic alloys can suppress CO poisoning and enhance the *OCHO adsorption during electrochemical CO2 reduction to formate.

Phase-Dependent Electrocatalytic CO2 Reduction on Pd3 Bi Nanocrystals.

Alloying is a general strategy for modulating the electronic structures of catalyst materials. Compared to more common solid-solution alloys, intermetallic alloys feature well-defined atomic arrangements and provide the unique platform for studying the structure-performance correlations. It is, unfortunately, synthetically challenging to prepare the nanostructures of intermetallic alloys for catalysis research. In this contribution, we prepare intermetallic Pd3 Bi nanocrystals of a uniform size via a facile solvothermal method. These nanocrystals can phase-transform into solid solution alloy via thermal annealing while retaining a similar composition and size. In 0.1 M KHCO3 aqueous solution, the intermetallic Pd3 Bi can selectively reduce CO2 to formate with high selectivity (≈100 %) and stability even at <-0.35 V versus reversible hydrogen electrode, whereas the solid solution alloy has limited formate selectivity of <60 %. Such unique phase-dependence is understood via theoretical simulations showing that the crystallographic ordering of Pd and Bi atoms within intermetallic alloys can suppress CO poisoning and enhance the *OCHO adsorption during electrochemical CO2 reduction to formate.

Electrochemical Generation of Hydrogen and Methanol using ITO Sheet Decorated with Modified-Titania as Electrode

Current issues of global warming and environmental pollution due to extensive use of fossil fuels has been reached to an alarming position. Being CO2 as main byproduct of fossil fuel consumption and water as abundantly available on earth surface has great potential to replace fossil fuels as energy source. Herein, electrocatalytic CO2 reduction with water for methanol and hydrogen gas (H2) production over ITO sheet decorated with modified-Titanium nanorods (TiO2 NR), has been investigated. The performance comparison of electrocatalytic activity of hydrothermally modified-titania with commercial TiO2 microparticles (MP) were further investigated. Electrochemical reactor containing KHCO3 aqueous solution with CO2 as an electrolyte and modified TiO2 nanorods (NR) as working electrodes offer an eco-friendly system to produce clean and sustainable energy system. The typical rates of product, i.e. methanol and H2 generation from the ITO sheet decorated with modified TiO2 NR layer recorded higher than those for the ITO sheet with commercial TiO2 microparticle. At 2.0V applied potential vs Ag/AgCl as reference electrode, the modified TiO2 NR electrocatalyst yielded methanol at a rate of 3.32 µmol.cm−2.L−1 and H2 at a rate of 6 µmol.cm−2.L−1 which was higher than that of commercial TiO2 MP electrocatalyst (methanol = 1.5 µmol.cm−2.L−1 and H2 = 3.7 µmol.cm−2.L−1). The enhancement in product yields of methanol and H2 was mainly due to the notable improvements and modification in texture of TiO2 working electrode interface. Hence, it is concluded that the modified TiO2 NR can be considered as a competent candidate for sustainable energy conversion applications. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

An Extrinsic Faradaic Layer on CuSn for High-Performance Electrocatalytic CO 2 Reduction

An Extrinsic Faradaic Layer on CuSn for High-Performance Electrocatalytic CO ₂ Reduction

A general strategy for obtaining BiOX nanoplates derived Bi nanosheets as efficient CO2 reduction catalysts by enhancing CO2•- adsorption and electron transfer

Electroreduction of carbon dioxide (CO2) into formic acid/formate has been considered as one of the most promising strategies for obtaining value-added fuels and chemical productions. Herein, we present a general method for preparing Bi-based electrocatalysts via in situ reduction of bismuth oxyiodide (BiOI) in CO2-saturated electrolyte. The precursors of BiOI nanoplates (P-nanoplates) with thickness of 30–40 nm could be easily obtained and provide a concise model to probe the mechanisms of CO2 reduction to formate. BiOI nanoplates precursors derived Bi nanosheets (P-nanoplates-Bi) exhibited an excellent performance for CO2 reduction to formate, achieving Faradaic efficiencies (FEs) over 80% in a wide potential window and a maximum FE approaching of 95% with a current density of 13.3 ± 0.6 mA cm−2 at −0.9 V versus reverse hydrogen electrode (υs. RHE). Such P-nanoplates-Bi nanosheets showed a stable electrocatalytic actitivity during 15 h operation in 0.5 M KHCO3 aqueous solution. The superior performance is mainly attributed to the two-dimensional (2D) Bi nanosheets, which can increase CO2•- adsorption, enlarge active surface area, show better reaction kinetics and provide lower contact resistance with accelerated electron transfer. For comparison, precursors of BiOI plate-like (P-bulk) with doubled thicknesses and ultrathin BiOI with a few nanometers derived Bi catalysts tend to agglomerate and appear as irregular structured Bi nanoparticles during the reaction. Their peak FEs for formate are much lower than those of P-nanoplates derived Bi nanosheets at −0.9 V.

Strengthen metal-oxygen covalency of CoFe-layered double hydroxide for efficient mild oxygen evolution

Oxygen evolution reaction (OER) is crucial for hydrogen production as well as other energy storage technologies. CoFe-layered double hydroxide (CoFe-OH) has been widely considered as one of the most efficient electrocatalysts for OER in basic aqueous solution. However, it still suffers from low activity in neutral electrolyte. This paper describes partially oxidized CoFe-OH (PO-CoFe-OH) with enhanced covalency of M-O bonds and displays enhanced OER performance under mild condition. Mechanism studies reveal the suitably enhanced M-O covalency in PO-CoFe-OH shifts the OER mechanism to lattice oxygen oxidation mechanism and also promotes the rate-limiting deprotonation, providing superior OER performance. It just requires the overpotentials of 186 and 365 mV to drive the current density densities of 1 and 10 mA·cm−2 in 0.1 M KHCO3 aqueous solution (pH = 8.3), respectively. It provides a new process for rational design of efficient catalysts for water oxidation in mild conditions.

Highly selective metal-organic framework-based electrocatalyst for the electrochemical reduction of CO2 to CO

Cu- and Zn-MOF74 were synthesized using the nitrate salts of Cu and Zn combined with 2,5-dihydroxyterephtalic acid (H4DOBBDC) by a simple solvothermal method. The as-prepared Cu- and Zn-MOF74 were used as electrocatalysts for the electrochemical reduction CO2 using a H-type cell in a 0.1 M of KHCO3 aqueous solution. The Cu-MOF74 exhibited a larger surface area, higher CO selectivity, smaller Tafel slope, and lower overpotential than those of Zn-MOF74. A computational simulation showed that the lower activation energy of Cu-MOF74 than that of Zn-MOF74 in the rate-determining step resulted in better electrocatalytic properties.

Nanoporous structured Sn‐MWCNT/Cu electrodes fabricated by electrodeposition–chemical dezincification for catalytic CO2 reduction

SummaryA facile method is developed to fabricate nanoporous, structured, Sn‐based catalyst electrodes. Sn, Zn, and multiwalled carbon nanotubes (MWCNTs) are co‐electrodeposited on a copper substrate, followed by chemical dezincification in NaOH aqueous solution to remove Zn. By controlling variables such as the contents of Zn and MWCNTs, a series of Sn‐MWCNT/Cu (SZMC) electrodes are fabricated. Experimental results show that using such novel SZMC electrodes can achieve a HCOO− Faradaic efficiency of over 91% at −0.99 V versus RHE for 10 hours in CO2‐saturated 0.5 M KHCO3 aqueous solution. The high performance is attributed to the addition of MWCNTs and Zn, followed by chemical dezincification to remove Zn and then create vacancies in the catalyst structure, which results in a special porous structure of SZMC with large surface area. Then ECSA is used for enhancing the catalytic activity and selectivity of HCOO− production, as well as promoting intermediate adsorption and mass transfer.