Copper-coordinated cellulose ion conductors for solid-state batteries.

Although solid-state lithium (Li)-metal batteries promise both high energy density and safety, existing solid ion conductors fail to satisfy the rigorous requirements of battery operations. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact with electrodes. Conversely, polymer ion conductors that are Li-metal-stable usually provide better interfacial compatibility and mechanical tolerance, but typically suffer from inferior ionic conductivity owing to the coupling of the ion transport with the motion of the polymer chains1-3. Here we report a general strategy for achieving high-performance solid polymer ion conductors by engineering of molecular channels. Through the coordination of copper ions (Cu2+) with one-dimensional cellulose nanofibrils, we show that the opening of molecular channels within the normally ion-insulating cellulose enables rapid transport of Li+ ions along the polymer chains. In addition to high Li+ conductivity (1.5 × 10-3 siemens per centimetre at room temperature along the molecular chain direction), the Cu2+-coordinated cellulose ion conductor also exhibits a high transference number (0.78, compared with 0.2-0.5 in other polymers2) and a wide window of electrochemical stability (0-4.5 volts) that can accommodate both the Li-metal anode and high-voltage cathodes. This one-dimensional ion conductor also allows ion percolation in thick LiFePO4 solid-state cathodes for application in batteries with a high energy density. Furthermore, we have verified the universality of this molecular-channel engineering approach with other polymers and cations, achieving similarly high conductivities, with implications that could go beyond safe, high-performance solid-state batteries.

Electrochemical Approaches for CO2 Conversion to Chemicals: A Journey toward Practical Applications.

Carbon capture, utilization, and sequestration play an essential role to address CO2 emissions. Among all carbon utilization technologies, CO2 electroreduction has gained immense interest due to its potential for directly converting CO2 to a variety of valuable commodity chemicals using clean, renewable electricity as the sole energy source. The research community has witnessed rapid advances in CO2 electrolysis technology in recent years, including highly selective catalysts, larger-scale reactors, specific process modeling, as well as a mechanistic understanding of the CO2 reduction reaction. The rapid advances in the field brings promise to the commercial application of the technology and the rapid rollout of the CO2 electroreduction for chemical manufacturing.This Account focuses on our contributions in both fundamental and applied research in the field of electrocatalytic CO2 and CO reduction reactions. We first discuss (1) the development of novel electrocatalysts for CO2/CO electroreduction to enhance the product selectivity and lower the energy consumption. Specifically, we synthesized nanoporous Ag and homogeneously mixed Cu-based bimetallic catalysts for the enhanced production of CO from CO2 and multicarbon products from CO, respectively. Then, we review our efforts in (2) the field of reactor engineering, including a dissolved CO2 H-type cell, vapor-fed CO2 three-compartment flow cell, and vapor-fed CO2 membrane electrode assembly, for enhancing reaction rates and scalability. Next, we describe (3) the investigation of reaction mechanisms using in situ and operando techniques, such as surface-enhanced vibrational spectroscopies and electrochemical mass spectroscopy. We revealed the participation of bicarbonate in CO2 electroreduction on Au using attenuated total-reflectance surface-enhanced infrared absorption spectroscopy, the presence of an "oxygenated" surface of Cu under CO electroreduction conditions using surface-enhanced Raman spectroscopy, and the origin of oxygen in acetaldehyde and other CO electroreduction products on Cu using flow electrolyzer mass spectrometry. Lastly, we examine (4) the commercial potential of the CO2 electrolysis technology, such as understanding pollutant effects in CO2 electroreduction and developing techno-economic analysis. Specifically, we discuss the effects of SO2 and NOx in CO2 electroreduction using Cu, Ag, and Sn catalysts. We also identify technical barriers that need to be overcome and offer our perspective on accelerating the commercial deployment of the CO2 electrolysis technology.

Electrochemical Reduction of Gaseous Nitrogen Oxides on Transition Metals at Ambient Conditions.

Mitigating nitrogen oxide (NOx) emissions is critical to tackle global warming and improve air quality. Conventional NOx abatement technologies for emission control suffer from a low efficiency at near ambient temperatures. Herein, we show an electrochemical pathway to reduce gaseous NOx that can be conducted at high reaction rates (400 mA cm-2) under ambient conditions. Various transition metals are evaluated for electrochemical reduction of NO and N2O to reveal the role of electrocatalyst in determining the product selectivity. Specifically, Cu is highly selective toward NH3 formation with >80% Faradaic efficiency in NO electroreduction. Furthermore, the partial pressure study of NO electroreduction revealed that a high NO coverage facilitates the N-N coupling reaction. In acidic electrolytes, the formation of NH3 is greatly favored, whereas the N2 production is suppressed. Additional mechanistic studies were conducted by using flow electrochemical mass spectrometry to gain further insights into reaction pathways. This work provides a promising avenue toward abating gaseous NOx emissions at ambient conditions by using renewable electricity.

Flow Electrolyzer Mass Spectrometry with a Gas-Diffusion Electrode Design.

Operando mass spectrometry is a powerful technique to probe reaction intermediates near the surface of catalyst in electrochemical systems. For electrochemical reactions involving gas reactants, conventional operando mass spectrometry struggles in detecting reaction intermediates because the batch-type electrochemical reactor can only handle a very limited current density due to the low solubility of gas reactant(s). Herein, we developed a new technique, namely flow electrolyzer mass spectrometry (FEMS), by incorporating a gas-diffusion electrode design, which enables the detection of reactive volatile or gaseous species at high operating current densities (>100 mA cm-2 ). We investigated the electrochemical carbon monoxide reduction reaction (eCORR) on polycrystalline copper and elucidated the oxygen incorporation mechanism in the acetaldehyde formation. Combining FEMS and isotopic labelling, we showed that the oxygen in the as-formed acetaldehyde intermediate originates from the reactant CO, while ethanol and n-propanol contained mainly solvent oxygen. The observation provides direct experimental evidence of an isotopic scrambling mechanism.

SO2-Induced Selectivity Change in CO2 Electroreduction.

Electrochemical conversion of carbon dioxide (CO2) to value-added chemicals has attracted much attention in recent years as a potential alternative to fossil resources. Although significant works have studied the influence of impurities in the electrolyte (e.g., metal ions), few studies have been performed to understand the influence of gaseous impurities in CO2 electroreduction. Herein, we study the effects of sulfur dioxide (SO2) on Ag-, Sn-, and Cu-catalyzed CO2 electrolysis in a flow-cell electrolyzer in near-neutral electrolyte, representing a broad range of CO2 reduction catalysts. We show that the presence of SO2 impurity reduces the efficiency of converting CO2 due to the preferential reduction of SO2. In the cases of Ag and Sn, the effect of SO2 impurity was reversible and the catalytic activities of both catalysts were recovered. On the contrary, a shift in selectivity toward formate accompanied by a suppression of multicarbon (C2+) products was observed on Cu catalyst, demonstrating that Cu is highly sensitive to SO2 impurity. Our results suggest that CO2 obtained from direct air capture technologies or biorefineries could be more suitable for Cu-catalyzed CO2 electrolysis as these CO2 sources would be relatively cleaner (SO2-free) than fossil-derived sources such as power plants and can be directly coupled with distributed renewable energy sources such as wind and solar.

Spontaneous Renal Artery Dissection as a Cause of Acute Renal Infarction: Clinical and MDCT Findings.

The purpose of this study was to assess the incidence of spontaneous renal artery dissection (SRAD) as a cause of acute renal infarction, and to evaluate the clinical and multidetector computed tomography (MDCT) findings of SRAD. From November 2011 to January 2014, 35 patients who were diagnosed with acute renal infarction by MDCT were included. We analyzed the 35 MDCT data sets and medical records retrospectively, and compared clinical and imaging features of SRAD with an embolism, using Fisher's exact test and the Mann-Whitney test. The most common cause of acute renal infarction was an embolism, and SRAD was the second most common cause. SRAD patients had new-onset hypertension more frequently than embolic patients. Embolic patients were found to have increased C-reactive protein (CRP) more often than SRAD patients. Laboratory results, including tests for lactate dehydrogenase (LDH) and blood urea nitrogen (BUN), and the BUN/creatinine ratio (BCR) were significantly higher in embolic patients than SRAD patients. Bilateral renal involvement was detected in embolic patients more often than in SRAD patients. MDCT images of SRAD patients showed the stenosis of the true lumen, due to compression by a thrombosed false lumen. None of SRAD patients progressed to an estimated glomerular filtration rate < 60 mL/min/1.73 m² or to end-stage renal disease during the follow-up period. SRAD is not a rare cause of acute renal infarction, and it has a benign clinical course. It should be considered in a differential diagnosis of acute renal infarction, particularly in patients with new-onset hypertension, unilateral renal involvement, and normal ranges of CRP, LDH, BUN, and BCR.

Scalable Gas Diffusion Electrode Fabrication for Electrochemical CO2 Reduction Using Physical Vapor Deposition Methods.

Electrochemical CO2 reduction (ECR) promises the replacement of fossil fuels as the source of feedstock chemicals and seasonal storage of renewable energy. While much progress has been made in catalyst development and electrochemical reactor design, few studies have addressed the effect of catalyst integration on device performance. Using a microfluidic gas diffusion electrolyzer, we systematically studied the effect of thickness and the morphology of electron beam (EB) and magnetron-sputtered (MS) Cu catalyst coatings on ECR performance. We observed that EB-Cu outperforms MS-Cu in current density, selectivity, and energy efficiency, with 400 nm thick catalyst coatings performing the best. The superior performance of EB-Cu catalysts is assigned to their faceted surface morphology and sharper Cu/gas diffusion layer interface, which increases their hydrophobicity. Tests in a large-scale zero-gap electrolyzer yielded similar product selectivity distributions with an ethylene Faradaic efficiency of 39% at 200 mA/cm2, demonstrating the scalability for industrial ECR applications.

The impact of nitrogen oxides on electrochemical carbon dioxide reduction.

The electroreduction of carbon dioxide offers a promising avenue to produce valuable fuels and chemicals using greenhouse gas carbon dioxide as the carbon feedstock. Because industrial carbon dioxide point sources often contain numerous contaminants, such as nitrogen oxides, understanding the potential impact of contaminants on carbon dioxide electrolysis is crucial for practical applications. Herein, we investigate the impact of various nitrogen oxides, including nitric oxide, nitrogen dioxide, and nitrous oxide, on carbon dioxide electroreduction on three model electrocatalysts (i.e., copper, silver, and tin). We demonstrate that the presence of nitrogen oxides (up to 0.83%) in the carbon dioxide feed leads to a considerable Faradaic efficiency loss in carbon dioxide electroreduction, which is caused by the preferential electroreduction of nitrogen oxides over carbon dioxide. The primary products of nitrogen oxides electroreduction include nitrous oxide, nitrogen, hydroxylamine, and ammonia. Despite the loss in Faradaic efficiency, the electrocatalysts exhibit similar carbon dioxide reduction performances once a pure carbon dioxide feed is restored, indicating a negligible long-term impact of nitrogen oxides on the catalytic properties of the model catalysts.

Overcoming immiscibility toward bimetallic catalyst library.

Bimetallics are emerging as important materials that often exhibit distinct chemical properties from monometallics. However, there is limited access to homogeneously alloyed bimetallics because of the thermodynamic immiscibility of the constituent elements. Overcoming the inherent immiscibility in bimetallic systems would create a bimetallic library with unique properties. Here, we present a nonequilibrium synthesis strategy to address the immiscibility challenge in bimetallics. As a proof of concept, we synthesize a broad range of homogeneously alloyed Cu-based bimetallic nanoparticles regardless of the thermodynamic immiscibility. The nonequilibrated bimetallic nanoparticles are further investigated as electrocatalysts for carbon monoxide reduction at commercially relevant current densities (>100 mA cm-2), in which Cu0.9Ni0.1 shows the highest multicarbon product Faradaic efficiency of ~76% with a current density of ~93 mA cm-2. The ability to overcome thermodynamic immiscibility in multimetallic synthesis offers freedom to design and synthesize new functional nanomaterials with desired chemical compositions and catalytic properties.

Formation of carbon-nitrogen bonds in carbon monoxide electrolysis.

The electroreduction of CO2 is a promising technology for carbon utilization. Although electrolysis of CO2 or CO2-derived CO can generate important industrial multicarbon feedstocks such as ethylene, ethanol, n-propanol and acetate, most efforts have been devoted to promoting C-C bond formation. Here, we demonstrate that C-N bonds can be formed through co-electrolysis of CO and NH3 with acetamide selectivity of nearly 40% at industrially relevant reaction rates. Full-solvent quantum mechanical calculations show that acetamide forms through nucleophilic addition of NH3 to a surface-bound ketene intermediate, a step that is in competition with OH- addition, which leads to acetate. The C-N formation mechanism was successfully extended to a series of amide products through amine nucleophilic attack on the ketene intermediate. This strategy enables us to form carbon-heteroatom bonds through the electroreduction of CO, expanding the scope of products available from CO2 reduction.

Segmental colonic involvement of plexiform neurofibroma in neurofibromatosis type 1.

In a 36-year-old man with neurofibromatosis type 1, rare colonic involvement of plexiform neurofibroma is presented. The diagnosis was confirmed by operation. Radiologic findings consisted of marked concentric thickening of the colonic wall with variable attenuation, namely, a "multilayer appearance," as well as clusters of multiple soft tissue nodules in the mesentery.