Determination of uric acid in synthetic urine by using electrochemical surface oxidation enhanced Raman scattering

In this work, a new and easy methodology to determine uric acid in relevant samples using Raman spectroelectrochemistry is presented. The spectroelectrochemistry experiment is based on the in-situ formation of a suitable substrate that enables the enhancement of the Raman signal of an analyte during the oxidation stage of a silver electrode. This phenomenon is known as electrochemical surface oxidation enhanced Raman scattering (EC-SOERS) and has proved to be useful in quantitative analysis using disposable screen printed electrodes. The successful combination of EC-SOERS with PARAFAC analysis allows the determination of uric acid in a relevant complex sample avoiding the use of standard addition method and without using a baseline correction, which simplifies the application of such methodology in routine analysis.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU297P18

Effect of chloride and pH on the electrochemical surface oxidation enhanced Raman scattering

In the present work, electrochemical surface oxidation enhanced Raman scattering (EC-SOERS) was studied using time resolved Raman spectroelectrochemistry. This multiresponse technique allows us to obtain dynamic information about the processes taking place during the electrochemical oxidation of a silver substrate. EC-SOERS is particularly found in specific electrolytic conditions, namely, HClO4 0.1 M + KCl 5·10−3 M, and has a clear dependence on chloride concentration and pH, being the optimum values between 5·10−3 M and 1·10−2 M for chloride and pH = 1. In light of the results of this study, the appearance of the phenomenon is related to the modification of the electrode surface, yielding Ag/AgCl cubes as plasmonic structures, and the stability of such structures at low pH values. The results presented in this work could shed more light into the intricate EC-SOERS phenomenon which can be summarized as the increase of the Raman signal for a Raman probe molecule exclusively during the electrochemical oxidation of silver electrodes.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU033-U16). J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16

Electrochemical SERS and SOERS in a single experiment: A new methodology for quantitative analysis

In the present work, a new methodology which combines two different phenomena to enhance the Raman signal is used to resolve a mixture of two compounds with similar molecular structures. The use of Raman spectroelectrochemistry (Raman-SEC) allows us to collect simultaneously, with high time-resolution, the enhancement of the Raman signal of the compounds present in a sample during the electrochemical oxidation-reduction cycle (ORC) of a silver screen-printed electrode. During such ORC two different phenomena appears depending on the stage of the electrochemical modification of the silver substrate, which are known as electrochemical surface enhanced Raman scattering (EC-SERS) and electrochemical surface oxidation enhanced Raman scattering (EC-SOERS). This work is a proof of concept that demonstrates the advantage of using EC-SOERS and EC-SERS in a single experiment to resolve mixtures of similar molecules such as vitamin B3, which components are nicotinic acid and nicotinamide. Although the interaction between analytes and substrates influence a univariate calibration, the trilinear character of Raman-SEC makes possible to deconvolve such interactions and provide a good calibration curve for both, nicotinic acid and nicotinamide.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (Grant BU033-U16 and BU297P18) and Ministerio de Ciencia, Innovación y Universidades (RED2018-102412-T). J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16

Engineering 3D Printed Structures Towards Electrochemically Driven Green Ammonia Synthesis: A Perspective

Broadening scope of 3D printing technology is recently identified as a potential strategy to mitigate concerns in the light of rising energy crisis and environmental imbalances. The importance of ammonia as a hydrogen carrier is well known and, in the context of 3D printing, designing and fabrication of electrode substrates for ammonia synthesis from nitrate sources will present a twofold advantage toward addressing the energy crisis and also limiting the harmful effect of excessive nitrate from the environment. Studies in the direction of employing 3D printed catalysts or reactors for ammonia production have been rarely reported. Thus, in this perspective article, the possibilities of engineering several 3D printed electrocatalysts for nitrate reduction to ammonia via various techniques are discussed and experimental demonstrations to substantiate the potential of 3D printed electrocatalysts toward ammonia production are provided, for the first time. In addition, postfabrication treatments, modification, and patterned coating of 3D printed substrates using active materials are also discussed along with the possibilities of fabricating catalysts for ammonia synthesis via nitrogen reduction reaction. Certain limitations and possible solutions of this printing technology for ammonia production are discussed along with the future outlook. Such timely discussions will be interesting for researchers and scientists for enhancing further possibilities toward broadening this field and toward other catalytic applications

Spectroelectrochemistry of Quantum Dots

Spectroelectrochemistry (SEC) is a set of techniques with many advantages in the study and characterization of materials. Although SEC has not yet been widely used to study quantum dots (QDs), the information extracted from SEC experiments about these nanostructures is very useful. Most of the works that use SEC to study QDs are high-quality pieces of research. This review intends to show how to perform SEC in an easy way and what information can be obtained using these techniques. Most of the examples shown in this review are related to semiconductor and carbon QDs. After a brief introduction, some optoelectronic properties of QDs and the main SEC techniques are described. The capabilities of SEC for the study of QDs are illustrated with examples extracted from literature. Finally, the needs of SEC to become a user-friendly technique and its evolution to become more powerful are commented in the last section of the review.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU033-U16 and BU297P18). J.G-R. thanks UBU for his postdoctoral contract. J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16). Thanks to J

Enhancement factors in electrochemical surface oxidation enhanced Raman scattering

Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS) is a new phenomenon that provokes the enhancement of the Raman signal during the oxidation of a metal surface. Studies carried out so far indicate that carbonyl and carboxyl group are necessary to observe this phenomenon with a delocated charge being an important factor. In this work, the enhancement factors of EC-SOERS for different molecules, which present highly delocated charge and a carboxyl group, have been assessed. The systematic study of the enhancement factors helps to shed more light on the interaction of the molecules with the electrochemically generated SOERS substrates, yielding key information about the properties and specific features of this intriguing phenomenon. For the first time, a systematic information about the enhancement factors of this phenomenon is obtained. Analytical enhancement factors higher than 105 are obtained.Ministerio de Economía, y Competitividad (Grant CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (Grant BU297P18) and Ministerio de Ciencia, Innovación y Universidades (Grant RED2018-102412-T). J.V.P-R. thanks Junta de Castilla y León for his postdoctoral fellowship (Grant BU033-U16)

Copper 3D-Printed Electrodes for Ammonia Electrosynthesis via Nitrate Reduction

Ammonia is critical to the world economy. However, nowadays the production of ammonia is exclusively carried out by the well-known Haber-Bosch process, which is an energy-intensive process that leads to a large amount of CO2 emissions. The search for alternative ammonia production routes is mandatory for a sustainable and zero emissions future economy. Electrochemical nitrate-to-ammonia conversion emerges as a suitable alternative to achieve decentralized ammonia production at a small scale with zero emissions perspective. Here, we fabricate copper electrodes by a three-dimensional (3D) printing technique, which allows for the point-of-use customizable fabrication of electrochemical systems, and use them for nitrate-to-ammonia conversion. By using the fused fabrication filament printing technique, Cu-based electrodes were prepared in an easy, fast, and scalable way from a Cu-containing filament. The electrode was used for nitrate-to-ammonia conversion, obtaining an outstanding faradaic efficiency (FE) of 96.5% and a high ammonia selectivity of 95%. The fabrication of a copper-based electrochemical system for nitrate-to-ammonia conversion paves the way for an on-demand, point-of-use scalable electrochemical system for ammonia production

Quantitative Raman spectroelectrochemistry using silver screen-printed electrodes

Surface enhanced Raman scattering (SERS) is a powerful technique based on the intensification of the Raman signal because of the interaction of a molecule with a nanostructured metal surface. Electrochemically roughened silver has been widely used as SERS substrate in the qualitative detection of analytes at the ultra-trace level. However, its potential for quantitative analysis has not been widely exploited yet. In this work, the combination of time-resolved Raman spectroelectrochemistry with silver screen-printed electrodes (SPE) is proposed as a novel methodology for the preparation of SERS substrates. The in situ activation of a SERS substrate is performed simultaneously with the analytical detection of a probe molecule, controlling the process related to the preparation of the substrate and performing the analytical measurement in real time. The results show the good performance of silver SPE as electrochemically-induced surface-enhanced Raman scattering substrates. Raman spectra were recorded at fairly low integration times (250 ms), obtaining useful spectroelectrochemical information of the processes occurring at the SPE surface with excellent time-resolution. By recording the microscopic surface images at different times during the experiment, we correlated the different data obtained: structural, optical and electrochemical. Finally, the in situ activation process was used to obtain a suitable in situ SERS signal for ferricyanide and tris(bipyridine)ruthenium (II) quantification. The detection of the analytes at concentrations of a few tens of nM was possible with a low integration time (2 s) and good precision, demonstrating the exceptional performance of the Raman spectroelectrochemical method and the possibility to use cost-effective screen-printed electrodes for applications where a high sensitivity is needed.Ministerio de Economía y Competitividad (CTQ2017-83935-R, CTQ2014-55583-R, TEC2014-51940-C2-2R, CTQ2015-71955-REDT) and Junta de Castilla y León (BU033-U16

The Role of Adsorption in the Electrocatalysis of Hydrazine on Platinum Electrodes

Hydrazine oxidation on platinum single-crystal electrodes has been studied in acidic solution containing different electrolytes. It will be shown that the hydrazinium cation is adsorbed on platinum through an anodic reaction. Moreover, in the presence of chloride, this adsorption process is favored owing to the formation of an ionic pair with adsorbed chloride. In spite of the enhanced adsorption of hydrazine species in the presence of chloride, higher overpotentials are measured in these media, which reveals that the oxidation of hydrazine not only requires adsorption, but also that the adsorption mode of the species facilitates the formation of the transition state to yield the final product.This work has been financially supported by the MINECO (Spain) and Generalitat Valenciana through projects CTQ2016-76221-P and PROMETEOII/2014/013, respectively

Fe-MOF catalytic nanoarchitectonic toward electrochemical ammonia production

Electrochemical reduction of nitrate into ammonia has lately been identified as one among the promising solutions to address the challenges triggered by the growing global energy demand. Exploring newer electrocatalyst materials is vital to make this process effective and feasible. Recently, metal−organic framework (MOF)-based catalysts are being well investigated for electrocatalytic ammonia synthesis, accounting for their enhanced structural and compositional integrity during catalytic reduction reactions. In this study, we investigate the ability of the PCN-250-Fe3 MOF toward ammonia production in its pristine and activated forms. The activated MOF catalyst delivered a faradaic efficiency of about 90% at −1 V vs RHE and a yield rate of 2.5 × 10−4 mol cm−2 h−1 , while the pristine catalyst delivered a 60% faradaic efficiency at the same potential. Theoretical studies further provide insights into the nitrate reduction reaction mechanism catalyzed by the PCN-250-Fe3 MOF catalyst. In short, simpler and cost effective strategies such as pretreatment of electrocatalysts have an upper hand in aggravating the intrinsic material properties, for catalytic applications, when compared to conventional material modification approaches.Web of Science1540473064729