Electrocatalytic Dinitrogen Reduction to Ammonia Using Easily Reducible N-Fused Cobalt Porphyrins.

Single-site molecular electrocatalysts, especially those that perform catalytic conversion of N2 to NH3 under mild conditions, are highly desirable to derive fundamental structure-activity relations and as potential alternatives to the current energy-consuming Haber-Bosch ammonia production process. Combining theoretical calculations with experimental evidence, it has been shown that easily reducible cobalt porphyrins catalyze the six-electron, six-proton reduction of dinitrogen to NH3 at neutral pH and under ambient conditions. Two easily reducible N-fused cobalt porphyrins - CoNHF and CoNHF(Br)2 - reveal NRR activity with Faradic efficiencies between 6 - 7.5% with ammonia yield rates of 300 - 340 µmol g-1 h-1.  Contrary to this, much harder-to-reduce N-fused porphyrins - CoNHF(Ph)2 and CoNHF(PE)2 - reveal no NRR activity. The present study highlights the significance of tuning the redox and structural properties of single-site NRR electrocatalysts for improved NRR activity under mild conditions.

Dinitrogen Reduction Coupled with Methanol Oxidation for Low Overpotential Electrochemical NH3 Synthesis Over Cobalt Pyrophosphate as Bifunctional Catalyst.

Electrochemical dinitrogen (N2 ) reduction to ammonia (NH3 ) coupled with methanol electro-oxidation is presented in the current work. Here, methanol oxidation reaction (MOR) is proposed as an alternative anode reaction to oxygen evolution reaction (OER) to accomplish electrons-induced reduction of N2 to NH3 at cathode and oxidation of methanol at anode in alkaline media thereby reducing the overall cell voltage for ammonia production. Cobalt pyrophosphate micro-flowers assembled by nanosheets are synthesized via a surfactant-assisted sonochemical approach. By virtue of structural and morphological advantages, the maximum Faradaic efficiency of 43.37% and NH3 yield rate of 159.6 µg h-1 mgca -1 is achieved at a potential of -0.2 V versus RHE. The proposed catalyst is shown to also exhibit a very high activity (100 mA mg-1 at 1.48 V), durability (2 h) and production of value-added formic acid at anode (2.78 µmol h-1 mgcat -1 and F.E. of 59.2%). The overall NH3 synthesis is achieved at a reduced cell voltage of 1.6 V (200 mV less than NRR-OER coupled NH3 synthesis) when OER at anode is replaced with MOR and a high NH3 yield rate of 95.2 µg h-1 mgcat -1 and HCOOH formation rate of 2.53 µmol h-1 mg-1 are witnessed under full-cell conditions.

Sustainable ammonia synthesis through electrochemical dinitrogen activation using an Ag2VO2PO4 catalyst.

Ammonia (NH3) is the second most produced chemical commodity with a worldwide production of 235 million tonnes in 2019, by virtue of its importance in fertilizer production, energy storage and transportation, and in the production of industrial chemicals. The most frequent method of NH3 production in large plants (1000 to 1500 t day-1) is the Haber-Bosch process, which has drawbacks of high greenhouse gas emissions (2.16 tonnes CO2 per tonne of NH3) and high energy consumption (over 30 GJ per tonne of NH3) due to high pressure and temperature conditions. For sustainable NH3 production, we require alternative green routes, wherein the electrochemical route holds huge potential due to reduced energy consumption and plant costs, higher selectivity, lower temperatures and pressures, and small to medium scale utilization of NH3. However, there are a number of challenges faced during the same viz. low production rates due to difficult N2 activation and reduced faradaic efficiency due to competing side reactions in aqueous electrolytes. Therefore, the most crucial aspect of electrochemical ammonia production technology is the design of an electrocatalyst which could activate the strong NN triple bond and effectively suppress the competing hydrogen evolution reaction (HER). In addition, the true NH3 yield estimation is of major concern due to the presence of possible N-contaminants, which may possibly lead to false estimation or overestimation of NH3. In this context, we have synthesized an Ag2VO2PO4 electrocatalyst with rice-grain like morphology via an energy efficient and less time consuming sonochemical method to carry out low temperature NH3 synthesis in an alkaline electrolyte. The choice of Ag metal and an alkaline environment effectually suppresses the HER and the bimetallic phosphate materials (Ag and V metals) induce high activity during nitrogen reduction, while rigorous analysis for tracing/elimination of N-labile and reducible species is considered for true NH3 production and assessment.

Tailoring cellulose paper via electroless CuSnB deposition for selective electrochemical detection of dopamine.

A novel, biodegradable substrate based, and cost-effective flexible electrochemical sensor was developed for the highly selective and sensitive detection of one of the major neurotransmitters, dopamine, which can be utilised as a disposable electrode for point-of-care diagnostic applications. The active material CuSnB decorated over cellulose paper exhibits good sensitivities of 3.92 µA µM-1 cm-2 with a limit of detection of 0.5 nM. Moreover, the flexible sensor demonstrated superior selectivity towards co-existing metabolites such as ascorbic acid, glucose, and uric acid, in addition to stability at various mechanical deformations.

Real-time screening of NixBy bifunctional electrocatalysts for overall NH3 synthesis via SG-TC SECM.

Electrochemical ammonia synthesis, which couples oxygen evolution at the anode with nitrogen reduction at the cathode, holds great significance for future food and energy needs. Both of these half-cell reactions determine the overall cell potential and efficiency of the process. However, the employment of different catalysts on either side, due to discrete mechanisms, increases the complexity and material processing costs of the system, where the designing of a bifunctional catalyst active towards both the NRR and OER is of huge significance. Unfortunately, the initial screening of the designed catalysts via physical characterizations, optical methods and other techniques, does not provide details about the electrochemical activity. The scanning electrochemical microscopy (SECM) technique can be useful to screen multi-catalysts at the same time for their electrochemical activities. Herein, we employed the sample generation-tip collection (SG-TC) mode of SECM to screen the designed NixBy catalysts before half-cell investigations, which suggested that the catalyst synthesized via sonochemical reduction (SR), i.e. NixBy (SR), was a better catalyst. This inference was in accordance with the half-cell NRR and OER measurements (FE: 49% for NH3 production, OER overpotential: 300 mV). By virtue of this remarkable bifunctional activity, the NRR-OER coupled full cell was assembled, which initiated the NH3 production at just 1.7 V and produced NH3 (1.08 mg h-1 mgcat-1) at the cathode and O2 (0.81 mg h-1 mgcat-1) at the anode after 2 h of electrolysis at 1.9 V.

Advances and Challenges in Nanomaterial-Based Electrochemical Immunosensors for Small Cell Lung Cancer Biomarker Neuron-Specific Enolase.

Early and rapid detection of neuron-specific enolase (NSE) is highly significant, as it is putative biomarker for small-cell lung cancer as well as COVID-19. Electrochemical techniques have attracted substantial attention for the early detection of cancer biomarkers due to the important properties of simplicity, high sensitivity, specificity, low cost, and point-of-care detection. This work reviews the clinically relevant labeled and label-free electrochemical immunosensors developed so far for the analysis of NSE. The prevailing role of nanostructured materials as electrode matrices is thoroughly discussed. Subsequently, the key performances of various immunoassays are critically evaluated in terms of limit of detection, linear ranges, and incubation time for clinical translation. Electrochemical techniques coupled with screen-printed electrodes developing market level commercialization of NSE sensors is also discussed. Finally, the review concludes with the current challenges associated with available methods and provides a future outlook toward commercialization opportunities for easy detection of NSE.

Flexible electrochemical sensor for highly sensitive and selective non-enzymatic detection of creatinine via electrodeposited copper over polymelamine formaldehyde.

A non-enzymatic electrochemical biosensor was developed for highly sensitive detection of creatinine using copper nanoparticles supported over polymelamine formaldehyde. The synergy between the electrodeposited copper nanoparticles over the highly porous polymer (eCu-PMF) provided a greener platform to boost up the electron transport at the electrode electrolyte interface by eliminating the role of redox species as well as interference of major interferents like glucose, dopamine, and ascorbic acid in physiological media 0.1 M PBS (pH 7.4). The proposed sensor exhibited a wide detection range of 100 fM-60 mM with high sensitivities of 0.320 mA nM-1 cm-2 and 3.8 mA nM-1 cm-2. Moreover, the sensor was applied to real samples of serum creatinine and recoveries of 97 to 114% were found. Additionally, a paper-based flexible screen-printed electrode was fabricated which displayed an excellent activity with the same detection range of 100 fM-60 mM and long-term storage stability of 15 days.

Selective Electrochemical Conversion of N2 to NH3 in Neutral Media Using B, N-Containing Carbon with a Nanotubular Morphology.

Electrochemical dinitrogen reduction (NRR) has riveted substantial attention as a greener method to synthesize ammonia (NH3) under ambient conditions. Here, B, N-containing carbon catalysts with a discrete morphology were synthesized from the metal-organic framework-ionic liquid (MOF-IL) composite for NRR in a neutral electrolyte medium (pH = 7). Morphology-dependent activity is witnessed, wherein C-BN@600 with a nanotubular morphology is able to achieve a high NH3 yield rate of 204 µg h-1 mgcat-1 and an F.E. of 16.7% with a TOF value of 0.2 h-1 at -0.2 V vs RHE. Further, a rigorous protocol is put forward for true NH3 estimation by tracing/eliminating any source of contamination in catalysts, electrolytes, or gas supply via ultraviolet-visible (UV-vis) spectroscopy, gas-purification methods, and isotope labeling experiments. Density functional theory predicts BN to be the favorable active site for N2 adsorption with a reduced energy barrier in the first reduction step and sequential stabilization of the B-N bond by an adjacent carbon atom.

Fabrication of NiFeB flexible electrode via electroless deposition towards selective and sensitive detection of dopamine.

A novel cost-effective and eco-friendly flexible electrochemical sensor was designed for highly selective and sensitive detection of dopamine to deal with the problems related to serious neurological disorders. The novel flexible paper electrode with NiFeB synthesised by simple dip-coating exhibits a high sensitivity of 35.35 µA µM-1 cm-2, 2.36 µA µM-1 cm-2 and 0.215 µA µM-1 cm-2 in the linear ranges from 10 nM to 1 µM, 5 µM to 50 µM and 100 µM to 400 µM, respectively, with an ultra-low detection limit of 2.1 nM. Besides, the free-standing flexible electrode for the detection of DA, the flexible paper sensor displayed superior selectivity towards various interferents, such as ascorbic acid, glucose and uric acid, as well as stability under various deformations.

Self-standing Fe3O4 decorated paper electrode as a binder-free trifunctional electrode for electrochemical ammonia synthesis and Zn-O2 batteries.

The conversion of the abundant biodegradable material into electroactive electrode material can be a good resource for sustainable energy conversion and storage applications. Herein, we present a simple, cost-effective and green approach for the fabrication of a flexible cellulose paper electrode using an electroless-electrodeposition method. The one-step electroless deposition route is followed to induce conductivity into a non-conductive cellulose paper substrate without using any expensive activators or sensitisers. The Fe3O4 is then electro-deposited as an active catalyst over the conductive paper substrate for use in electrochemical activities. The as-fabricated paper electrode shows promising activity and stability during the dinitrogen reduction reaction (NRR) as well as oxygen bifunctional electrocatalysis. A faradaic efficiency of 4.32% with a yield rate of 245 µg h-1 mgcat-1 at -0.1 V is achieved for NRR whereas a very small overpotential of 180 mV is required to reach 10 mA cm-2 during OER, and the ORR reaction starts at the onset potential of 0.86 V. The practical applicability of the paper electrode is validated by assembling a Zn-O2 battery showing a peak power density of 81 mW cm-2 and a stability up to 35 h during charge-discharge cycles, which can power the NRR to produce NH3 under full cell conditions.