Synergistic Effects of the Electric Field Induced by Imidazolium Rotation and Hydrogen Bonding in Electrocatalysis of CO2.

The roles of the ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and water in controlling the mechanism, energetics, and electrocatalytic activity of CO2 reduction to CO on silver in nonaqueous electrolytes were investigated. The first electron transfer occurs to CO2 at reduced overpotentials when it is trapped between the planes of the [EMIM]+ ring and the electrode surface due to cation reorientation as determined from voltammetry, in situ surface-enhanced Raman spectroscopy, and density functional theory calculations. Within this interface, water up to 0.5 M does not induce significant Faradaic activity, opposing the notion of it being a free proton source. Instead, water acts as a hydrogen bond donor, and the proton is sourced from [EMIM]+. Furthermore, this study demonstrates that alcohols with varying acidities tune the hydrogen bonding network in the interfacial microenvironment to lower the energetics required for CO2 reduction. The hydrogen bonding suppresses the formation of inactive carboxylate species, thus preserving the catalytic activity of [EMIM]+. The ability to tune the hydrogen bonding network opens new avenues for advancing IL-mediated electrocatalytic reactions in nonaqueous electrolytes.

Reactive capture and electrochemical conversion of CO2 with ionic liquids and deep eutectic solvents.

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture and conversion (RCC) of CO2 due to their wide electrochemical stability window, low volatility, and high CO2 solubility. There is environmental and economic interest in the direct utilization of the captured CO2 using electrified and modular processes that forgo the thermal- or pressure-swing regeneration steps to concentrate CO2, eliminating the need to compress, transport, or store the gas. The conventional electrochemical conversion of CO2 with aqueous electrolytes presents limited CO2 solubility and high energy requirement to achieve industrially relevant products. Additionally, aqueous systems have competitive hydrogen evolution. In the past decade, there has been significant progress toward the design of ILs and DESs, and their composites to separate CO2 from dilute streams. In parallel, but not necessarily in synergy, there have been studies focused on a few select ILs and DESs for electrochemical reduction of CO2, often diluting them with aqueous or non-aqueous solvents. The resulting electrode-electrolyte interfaces present a complex speciation for RCC. In this review, we describe how the ILs and DESs are tuned for RCC and specifically address the CO2 chemisorption and electroreduction mechanisms. Critical bulk and interfacial properties of ILs and DESs are discussed in the context of RCC, and the potential of these electrolytes are presented through a techno-economic evaluation.

Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO2.

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO2 (ECO2R) due to their role in the double-layer structure formation and increased CO2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same, considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO2R including the reference electrode, working electrode construction, cosolvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL with cosolvents (i.e. acetonitrile, dimethylformamide, dimethyl sulfoxide, propylene carbonate, and n-methyl-2-pyrrolidone) affects conductivity, CO2 mass transport, and ECO2R activation overpotential together with the effects of electrode materials (Sn, Ag, Au, and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO2R activity of molecular catalysts Ni(cyclam)Cl2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on the carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining nontraditional multifunctional electrolytes amenable to integrated CO2 capture and conversion technologies for homogeneous and heterogeneous ECO2R.

Understanding the Electrode-Electrolyte Interfaces of Ionic Liquids and Deep Eutectic Solvents.

Developing unconventional electrolytes such as ionic liquids (ILs) and deep eutectic solvents (DESs) has led to remarkable advances in electrochemical energy storage and conversion devices. However, the understanding of the electrode-electrolyte interfaces of these electrolytes, specifically the liquid structure and the charge/electron transfer mechanism and rates, is lacking due to the complexity of molecular interactions, the difficulty in studying the buried interfaces with nanometer-scale resolution, and the distribution of the time scales for the various interfacial events. This Feature Article outlines the standing questions in the field, summarizes some of the exciting approaches and results, and discusses our contributions to probing the electrified interfaces by electrochemical impedance spectroscopy (EIS), surface-enhanced Raman spectroscopy (SERS), and neutron reflectivity (NR). The related findings are analyzed within electrical double-layer models to provide a framework for studying ILs, DESs, and, more broadly, the concentrated hydrogen-bonded electrolytes.

Tailoring Electrochemical CO2 Reduction on Copper by Reactive Ionic Liquid and Native Hydrogen Bond Donors.

Electrochemical CO2 reduction (CO2 RR) on copper (Cu) shows promise for higher-value products beyond CO. However, challenges such as the limited CO2 solubility, high overpotentials, and the competing hydrogen evolution reaction (HER) in aqueous electrolytes hinder the practical realization. We propose a functionalized ionic liquid (IL) which generates ion-CO2 adducts and a hydrogen bond donor (HBD) upon CO2 absorption to modulate CO2 RR on Cu in a non-aqueous electrolyte. As revealed by transient voltammetry, electrochemical impedance spectroscopy (EIS), and in situ surface-enhanced Raman spectroscopy (SERS) complemented with image charge augmented quantum-mechanical/molecular mechanics (IC-QM/MM) computations, a unique microenvironment is constructed. In this microenvironment, the catalytic activity is primarily governed by the IL and HBD concentrations; former controlling the double layer thickness and the latter modulating the local proton availability. This translates to ample CO2 availability, reduced overpotential, and suppressed HER where C4 products are obtained. This study deepens the understanding of electrolyte effects in CO2 RR and the role of IL ions towards electrocatalytic microenvironment design.

A Bifunctional Ionic Liquid for Capture and Electrochemical Conversion of CO2 to CO over Silver.

Electrochemical conversion of CO2 requires selective catalysts and high solubility of CO2 in the electrolyte to reduce the energy requirement and increase the current efficiency. In this study, the CO2 reduction reaction (CO2RR) over Ag electrodes in acetonitrile-based electrolytes containing 0.1 M [EMIM][2-CNpyr] (1-ethyl-3-methylimidazolium 2-cyanopyrolide), a reactive ionic liquid (IL), is shown to selectively (>94%) convert CO2 to CO with a stable current density (6 mA·cm-2) for at least 12 h. The linear sweep voltammetry experiments show the onset potential of CO2 reduction in acetonitrile shifts positively by 240 mV when [EMIM][2-CNpyr] is added. This is attributed to the pre-activation of CO2 through the carboxylate formation via the carbene intermediate of the [EMIM]+ cation and the carbamate formation via binding to the nucleophilic [2-CNpyr]- anion. The analysis of the electrode-electrolyte interface by surface-enhanced Raman spectroscopy (SERS) confirms the catalytic role of the functionalized IL where the accumulation of the IL-CO2 adduct between -1.7 and -2.3 V vs Ag/Ag+ and the simultaneous CO formation are captured. This study reveals the electrode surface species and the role of the functionalized ions in lowering the energy requirement of CO2RR for the design of multifunctional electrolytes for the integrated capture and conversion.

Heart transplantation after Fontan procedure in adults.

Complex congenital heart disease is the cause for 1.5%-2.4% of heart transplantations in adults. Indications for heart transplantation are ventricular dysfunction, failed Fontan physiology, and cyanosis. We present a 43-year-old man, 20 years after a Fontan operation by an univentricular heart, with a tricuspid atresia, L-Transposition of the Great Arteries, and high-grade subpulmonary stenosis. Persistent bleeding after successful transplantation necessitated major blood transfusions and reoperation. We reconstructed superior vena cava and vena brachiocephalica using a pericardial patch, and because of postoperative low output syndrome, he was connected to extracorporeal circulation through cannulation of femoral artery and explanted after hemodynamic stability. Heart transplantation can be successful in patients with end-stage congenital heart diseases after Fontan procedure, because of improved surgical and medical management. Challenges include limited ability to assess hemodynamics, complex anatomy, increased risk of bleeding caused by multiple prior procedures, and unique underlying pathologic states. Careful patient selection and surgical timing are essential to increase long-term survival.

Surgical repair of congenital supravalvular aortic stenosis in adult.

Supravalvular aortic stenosis is a rare congenital cardiac anomaly occurring mainly as a part of Williams-Beuren syndrome. Aortic narrowing above the level of the aortic valve causes obstruction of the left ventricular outflow tract, and a pressure gradient between the left ventricle and the aorta causes left ventricle hypertrophy. We report here a case of a 22-year-old man who underwent extended patch aortoplasty because of supravalvular aortic stenosis accompanying Williams-Beuren syndrome. He was in New York Heart Association functional class III with localized hourglass type supravalvular aortic stenosis. Related to arterial hypertension he was in a cardiac decompensation. Mean pressure gradient was 73 mm Hg and maximum gradient 104 mm Hg. Electrocardiography indicated left ventricle hypertrophy, which was also seen in x-ray, as heart enlargement. We successfully treated this patient with extended patch aortoplasty and immediate postoperative echocardiography showed reduction of gradient. Good surgical outcome of congenital supravalvular aortic stenosis in adults can be achieved with this treatment. This technique provides symmetric reconstruction of the aorta with good postoperative results and no gradient across aortic valve and aortic valve insufficiency remains, providing excellent long-term relief of localized supravalvular gradients and preservation of aortic valve competence.

Heart transplantation in adults with congenital heart disease: experience with 15 patients.

End-stage congenital heart disease (CHD) is an important indication for pediatric heart transplantation (HTx) as well as transplantation in adult populations. The purpose of this retrospective analysis was to compare the survival rate of adults who underwent HTx for end-stage CHD with those who underwent HTx for other causes. To find out whether HTx is a viable therapeutic option for adult patients with preoperated CHD, data from 15 adult patients with different forms of CHD, who had previously undergone different corrective and palliative procedures, were retrospectively analyzed and compared with the HTx data of 1400 adult patients (>15 years old) whose indications for HTx were other than end-stage CHD. From 1989 to 2005, 15 adult patients (eight men/seven women) were given transplantation for end-stage CHD. Ten patients had been preoperated once, five patients twice. Their mean age was 34.06 +/- 3.9 years. In five cases, patients had development of acute renal failure. One female patient died 40 days after surgery, after having a cerebral infarction; one male patient died 4 years after HTx for OKT 3 monoclonal antibody-resistant rejection; and two patients died as the result of multiple organ failure at 4 days and 30 days after HTx, respectively; 11 patients are still alive. The cumulative survival rate at 1 year is 80% versus 80% in patients given transplantation for noncongenital indications. Heart transplantation in adults with end-stage CHD can be performed with a good long-term prognosis. Previous palliative operations do not affect outcome after HTx.

Outcome of heart transplantation in pediatric recipients: experience in 128 patients.

The purpose of this study was to review the outcome of pediatric heart recipients with uncorrectable congenital heart disease, failed corrective procedures, or intractable acquired cardiomyopathy. Between 1988 and 2005, cardiac transplantations were performed in 128 pediatric patients (59 girls and 69 boys) at the Heart-Center North-Rhine-Westphalia. Their ages varied between 1 week and 18 years (mean, 7.6 +/- 6.2 years). Underlying diseases were dilative cardiomyopathy in 93 cases and uncorrectable congenital heart disease in 35 cases. We diagnosed and observed 130 episodes of acute rejection in 85 patients (65.3% of patients had an acute rejection during the observation period); 71 patients were treated efficiently with steroid-pulse therapy. Monoclonal antibody OKT3 was administrated in 14 patients because of steroid-resistant acute donor organ rejection. Five of those 14 patients survived. The cumulative survival was 88% after 1 year and 68% after 10 years for all patients. Orthotopic heart transplantation is the ultimate treatment option for children with end-stage heart disease and shows an acceptable perioperative mortality rate as well as good long-term results.

Heart transplantation in children after mechanical circulatory support: comparison of heart transplantation with ventricular assist devices and elective heart transplantation.

Heart transplantation (HTx) is an ultimate treatment for children with end-stage heart failure or inoperable congenital heart disease. The supply of hearts is inadequate; therefore, different mechanical support systems must be used as bridge to HTx in pediatric patients with postoperative low output. The use of ventricular assist devices (VADs) as bridge to HTx in children is limited because of size differences. The purpose of this study was to evaluate the overall long-term outcome of pediatric circulatory support before pediatric HTx. From 1989 through 2004, 91 pediatric patients underwent isolated HTx. Seven of them required mechanical support before transplantation. We reviewed retrospectively the course of 91 children (mean age 14.7 years) who underwent HTx. Group A consisted of elective HTx patients who were treated as outpatients before HTx, whereas group B was the VAD-HTx bridging group (n=7; mean age 12.31 +/- 2.8 years). Mean duration of VAD support was 108 +/- 98 days (minimum 1 day, maximum 258 days). Overall survival rate after HTx was 80% at 1 year without significant differences between groups. Five of seven patients survived and could be discharged after successful HTx, for a survival rate of 77%. The mean follow-up period was 16.76 +/- 10.6 months. No differences in posttransplantation long-term survival and rejection episodes occurred between patients transplanted with or without VAD. VAD therapy can keep pediatric patients with end-stage heart failure alive until successful HTx, and bridge to HTx is a safe procedure in pediatric patients. After HTx, survival rates of these children are similar to those of patients awaiting elective HTx.