We demonstrate a simple strategy to enhance the CO reduction reaction (CO RR) selectivity by applying a pulsed electrochemical potential to a polycrystalline copper electrode. By controlling the pulse duration, we show that the hydrogen evolution reaction (HER) is highly suppressed to a fraction of the original value (<5 % faradaic efficiency) and selectivity for the CO RR dramatically improves (>75 % CH and >50 % CO faradaic efficiency). We attribute the improved CO RR selectivity to a dynamically rearranging surface coverage of hydrogen and intermediate species during the pulsing. Our finding provides new insights into the interplay of transport and reaction processes as well as timescales of competing pathways to enable new opportunities to tune CO RR selectivity by adjusting the pulse profile. Additionally, the pulsed potential method we describe can be easily applied to other catalysts materials to improve their CO RR selectivity.

Pulsing the potential during the electrochemical CO2 reduction (CO2R) reaction using copper has been shown to influence product selectivity (i.e., to suppress the undesired hydrogen evolution reaction (HER)) and to improve electrocatalyst stability compared to the constant applied potential. However, the underlying mechanism and contribution of interfacial/surface phenomena behind the pulsed potential application remain largely unknown. We investigated the state of the copper surface during the pulsed potential electrochemical CO2R using in situ X-ray adsorption near-edge spectroscopy (XANES). We probed the surface valence of the metallic electrode and found that the Cu electrode remains metallic over a broad pulsed potential range and only oxidizes to form Cu­(OH)2 in the bulk when the pulsed potential reaches the highly oxidative limit (greater than 0.6 V vs reversible hydrogen electrode (RHE)). Our results suggest that the pulsed anodic potential influences the interfacial species on the electrode surface, i.e., the dynamic competition between protons and hydroxide adsorbates instead of bulk copper oxidation. We attribute the suppressed HER to the electroadsorption of hydroxides, which outcompetes protons for surface sites. As shown in a recent in situ infrared study [IijimaG. Iijima, G. ACS Catalysis201996305, adsorbed hydroxides promote CO adsorption, a crucial CO2 reduction intermediate, by preventing CO from becoming inert through a near-neighbor effect. We corroborate this interpretation by demonstrating that the pulsed potential application can suppress the HER during the CO reduction just as the CO2R. Our results suggest that the pulsed potential mechanism favors CO2R over the HER due to two effects: (1) proton desorption/displacement during the anodic potential and (2) the accumulation of OHads creating a higher pH–surface environment, promoting CO adsorption. We can describe this pulsed potential dynamic interfacial mechanism in a competing quaternary Langmuir isotherm model. The insights from this investigation have wide-ranging implications for applying pulsed potential profiles to improve other electrochemical reactions.

With rising CO2 emissions and growing interests towards CO2 valorization, electrochemical CO2 reduction (eCO2R) has emerged as a promising prospect for carbon recycling and chemical energy storage. Yet, product selectivity and electrocatalyst longevity persist as obstacles to the broad implementation of eCO2R. A possible solution to ameliorate this challenge is to pulse the applied potential. However, it is currently unclear whether and how the trends and lessons obtained from the more conventional constant potential eCO2R translate to pulsed potential eCO2R. In this work, we report that the relationship between electrolyte concentration/composition and product distribution for pulsed potential eCO2R is different from constant potential eCO2R. In the case of constant potential eCO2R, increasing KHCO3 concentration favors the formation of H2 and CH4. In contrast, for pulsed potential eCO2R, H2 formation is suppressed due to the periodic desorption of surface protons, while CH4 is still favored. In the case of KCl, increasing the concentration during constant potential eCO2R does not affect product distribution, mainly producing H2 and CO. However, increasing KCl concentration during pulsed potential eCO2R persistently suppresses H2 formation and greatly favors C2 products, reaching 71 % Faradaic efficiency. Collectively, these results provide new mechanistic insights into the pulsed eCO2R mechanism within the context of proton‐donator ability and ionic conductivity.

Nucleic acid amplification tests are the gold standard for many infectious disease diagnoses due to high sensitivity and specificity, rapid operation, and low limits of detection. Despite the advantages of nucleic acid amplification tests, they currently offer limited point-of-care (POC) utility due to the need for complex instruments and laborious sample preparation. We report the development of the Nucleic Acid Isotachophoresis LAMP (NAIL) diagnostic device. NAIL uses isotachophoresis (ITP) and loop-mediated isothermal amplification (LAMP) to extract and amplify nucleic acids from complex matrices in less than one hour inside of an integrated chip. ITP is an electrokinetic separation technique that uses an electric field and two buffers to extract and purify nucleic acids in a single step. LAMP amplifies nucleic acids at constant temperature and produces large amounts of DNA that can be easily detected. A mobile phone images the amplification results to eliminate the need for laser fluorescent detection. The device requires minimal user intervention because capillary valves and heated air chambers act as passive valves and pumps for automated fluid actuation. In this paper, we describe NAIL device design and operation, and demonstrate the extraction and detection of pathogenic E. coli O157:H7 cells from whole milk samples. We use the Clinical and Laboratory Standards Institute (CLSI) limit of detection (LoD) definitions that take into account the variance from both positive and negative samples to determine the diagnostic LoD. According to the CLSI definition, the NAIL device has a limit of detection (LoD) of 1000 CFU mL(-1) for E. coli cells artificially inoculated into whole milk, which is two orders of magnitude improvement to standard tube-LAMP reactions with diluted milk samples and comparable to lab-based methods. The NAIL device potentially offers significant reductions in the complexity and cost of traditional nucleic acid diagnostics for POC applications.

We demonstrate a simple strategy to enhance the CO2 reduction reaction (CO2RR) selectivity by applying a pulsed electrochemical potential to a flat polycrystalline Cu electrode. By controlling the duration and magnitude of the cathodic and anodic pulses, we show that the selectivity for the CO2RR dramatically improves above 97% faradaic efficiency (FE) and consequently suppresses the competing hydrogen evolution reaction. Selectivity toward methane was found to be up to 83% FE – an unprecedented level of selectivity for a flat polycrystalline Cu electrode. The product output was also found to be tunable toward C2H4 and CO depending on the pulse profile applied. Here we investigate three alternate hypotheses and present evidence to disentangle the complex interplay of mass transport, surface coverage, and facet reconfiguration. We conducted CO reduction, rotating disk electrode tests, and in-situ XAS experiments, as well as coupled transport modelling to discern the exact mechanism. Additionally, to further understand the role of dynamic changes in the surface structure we tested CuO, Au, and Mo2C, which were found to also improve selectivity of products. These results show that pulsing dependence is not unique to Cu, but a more general phenomenon. Our findings provide new insights into the timescales of competing pathways. It also enables an opportunity to further improve the performance of next generation electrocatalyst materials.

The Cover Feature shows the pulse of electrochemical CO2 reduction: pulsing the applied potential provides a rich parameter space of previously under appreciated ‘knobs’ to tailor the selectivity of reduced products. More information can be found in the Full Paper by Kimura et al. on page 1781 in Issue 11, 2018 (DOI: 10.1002/cssc.201800318).

Battery management system (BMS) is a key component of the battery for electric vehicles and portable electronics, as it guaranties reliable and safe operation of the battery, while ensuring its longevity and optimal performance. State-of-the-art BMS relies on an equivalent circuit model, while an important research topic is the development of BMS, which is based on an electrochemical model.[1] The main task of BMS is to accurately estimate the available energy and power of the battery by tracking its current state of charge (SOC). The open circuit voltage (OCV) of a cell is often used for estimation of the SOC of a battery. It depends on the open circuit potential (OCP) of the anode and the cathode materials, which give the potential associated with a certain amount of lithium stored in each structure. The accuracy of the OCP curves of each electrode material is critical for use with BMS based on electrochemical models, as in addition to tracking the bulk SOC of a battery, it also tracks the surface SOC.[1] As a result, BMS based on electrochemical models can offer improved prediction for both instantaneous and pulse power relative to systems based on an equivalent circuit model. In this contribution, we propose a novel method for characterization of the open circuit potential vs. state of lithiation (OCP) curves for active materials commonly used in lithium-ion batteries. Our method offers increased accuracy over existing electrochemical procedures [1-3]by providing a standardized mapping process from the measured gravimetric capacity to state of lithiation and improving characterization in the region of the curve that is close to the lithium content of 1. We demonstrate the strengths of the method on two different cathode materials: LiCoO2 and LiNi1/3Mn1/3Co1/3O2, which are widely used in commercial cells for portable electronics and electric vehicles. [2-3] 1. Chaturvedi, N. A., Klein, R., Christensen, J., Ahmed, J. & Kojic, A. Algorithms for Advanced battery-Management Systems. IEEE Control Syst. Mag. 49–68 (2010). 2. Daniel, C., Mohanty, D., Li, J. & Wood, D. L. Cathode materials review. AIP Conf. Proc. 1597, 26–43 (2014). 3. Cairns, E. J. & Albertus, P. Batteries for Electric and Hybrid-Electric Vehicles. Annu. Rev. Chem. Biomol. Eng. 1, 299–320 (2010).

The ability to control reaction kinetics and double layer species during an electrocatalytic process is highly desirable, especially for electrochemical CO2 reduction (CO2R) — a complex process in which multiple reaction steps are competing on the electrode surface. Here we show evidence suggesting the double layer can be disrupted with the application of a pulsed potential during CO2R. Pulsing the potential during CO2R using copper has been shown to influence product selectivity (i.e., to suppress the undesired hydrogen evolution reaction (HER)) and to improve electrocatalyst stability compared to constant applied potential.1 However, the underlying mechanism and contribution of interfacial/surface phenomena behind the pulsed potential application remain largely unknown. To uncover this unknown we investigated the state of the copper surface during the pulsed potential electrochemical CO2R using in-situ X-ray Adsorption Near Edge Spectroscopy (XANES). We probed the surface valence of the metallic electrode and found that the Cu electrode remains metallic over a broad pulsed potential range and only oxidizes to form Cu(OH)2 in the bulk when the pulsed potential reaches a highly oxidative limit (> 0.6 V vs. reversible hydrogen electrode (RHE)). Our results suggest that the pulsed anodic potential influences the double layer on the electrode surface, i.e., the dynamic competition between protons and hydroxide adsorbates instead of bulk copper oxidation. We attribute the suppressed HER to the electro-adsorption of hydroxides, which outcompetes protons for surface sites. As shown in a recent in-situ infrared study2, adsorbed hydroxides promote CO adsorption, a crucial CO2 reduction intermediate, by preventing CO from becoming inert through a near neighbor effect. We corroborate this interpretation by demonstrating that the pulsed potential application can suppress the HER during the CO reduction just as the CO2R. Our results suggest that the pulsed potential mechanism favors CO2R over the HER due to two effects: 1) proton desorption/displacement during the anodic potential and 2) the accumulation of OHads creating a higher surface-pH environment, promoting CO adsorption. We can describe this pulsed potential dynamic double layer mechanism in a competing quaternary Langmuir isotherm model. We conclude that the active disruption of the double layer can be leveraged to tune the surface reaction environment during CO2R. Furthermore, the insights from this investigation have wide-ranging implications for applying pulsed potential profiles to improve electrocatalytic processes in general by dynamically disrupting double layer species. [1] Kimura, K. W.; Fritz, K. E.; Kim, J.; Suntivich, J.; Abruña, H. D.; Hanrath, T. Controlled Selectivity of CO2 Reduction on Copper by Pulsing the Electrochemical Potential. ChemSusChem 2018, 11 (11), 1781–1786. https://doi.org/10.1002/cssc.201800318. [2] Iijima, G.; Inomata, T.; Yamaguchi, H.; Ito, M.; Masuda, H. Role of a Hydroxide Layer on Cu Electrodes in Electrochemical CO2 Reduction. ACS Catal. 2019, 9 (7), 6305–6319. https://doi.org/10.1021/acscatal.9b00896.