Lewis acid-dominated aqueous electrolyte acting as co-catalyst and overcoming N2 activation issues on catalyst surface.

The growing demands for ammonia in agriculture and transportation fuel stimulate researchers to develop sustainable electrochemical methods to synthesize ammonia ambiently, to get past the energy-intensive Haber-Bosch process. However, the conventionally used aqueous electrolytes limit N2 solubility, leading to insufficient reactant molecules in the vicinity of the catalyst during electrochemical nitrogen reduction reaction (NRR). This hampers the yield and production rate of ammonia, irrespective of how efficient the catalyst is. Herein, we introduce an aqueous electrolyte (NaBF4), which not only acts as an N2-carrier in the medium but also works as a full-fledged "co-catalyst" along with our active material MnN4 to deliver a high yield of NH3 (328.59 µg h-1 mgcat-1) at 0.0 V versus reversible hydrogen electrode. BF3-induced charge polarization shifts the metal d-band center of the MnN4 unit close to the Fermi level, inviting N2 adsorption facilely. The Lewis acidity of the free BF3 molecules further propagates their importance in polarizing the N≡N bond of the adsorbed N2 and its first protonation. This push-pull kind of electronic interaction has been confirmed from the change in d-band center values of the MnN4 site as well as charge density distribution over our active model units, which turned out to be effective enough to lower the energy barrier of the potential determining steps of NRR. Consequently, a high production rate of NH3 (2.45 × 10-9 mol s-1 cm-2) was achieved, approaching the industrial scale where the source of NH3 was thoroughly studied and confirmed to be chiefly from the electrochemical reduction of the purged N2 gas.

Pd "Kills Two Birds with One Stone" for the Synthesis of Catalyst: Dual Active Sites of Pd Triggers the Kinetics of O2 Electrocatalysis.

Noble metal-based catalyst, despite their exorbitant cost, are the only successful catalyst for bifunctional oxygen electrocatalysis owing to their capability to drive forward the reaction rate kinetically. Therefore, it is desirable to diminish the noble metal loading without any compromise in the catalyst performance. In this study, the aim to achieve two goals with one action via a single-step route to have ultra-low loading of Pd in the catalyst. The Pd is used as a catalyst for C─C bond formation followed by complexation reactions or vice versa, in conventional Suzuki-Miyaura cross-coupling (SMCC) reaction, which yields a Pd-based porous organic polymer. Interestingly, it is found that dispersed Pd nanocluster (PdNC ) is present together with Pd single atom doped into nanocarbon (Pd-NC) matrix in the catalyst (PdNC /Pd-NC800 ) that obtained after pyrolysis of the porous polymer. The catalyst exhibits remarkable bifunctional activity and durability towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Further, it is studied that the in situ attenuated total reflection infrared (ATR-IR) spectroscopy at different electrochemical potentials during ORR and OER to observe the reaction intermediates. The homemade zinc-air battery with the catalyst displayed great performance, establishing the significance of PdNC /Pd-NC800 as a bifunctional oxygen electrocatalyst.

Coordination Structure Modulation in Group-VIB Metal Doped Ag3PO4 Augments Active Site Density for Electrocatalytic Conversion of N2 to NH3.

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag3PO4 to enhance the active site density, accompanied by d-p orbital mixing at the active site/N2 interface. Doping induces compressive strain in the Ag3PO4 lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N2 adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N2H4, which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N2 to NH3 on Mo/Ag3PO4-10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR.

Engineering Catalytically Active Sites by Sculpting Artificial Edges on MoS2 Basal Plane for Dinitrogen Reduction at a Low Overpotential.

Engineering catalytically active sites have been a challenge so far and often relies on optimization of synthesis routes, which can at most provide quantitative enhancement of active facets, however, cannot provide control over choosing orientation, geometry and spatial distribution of the active sites. Artificially sculpting catalytically active sites via laser-etching technique can provide a new prospect in this field and offer a new species of nanocatalyst for achieving superior selectivity and attaining maximum yield via absolute control over defining their location and geometry of every active site at a nanoscale precision. In this work, a controlled protocol of artificial surface engineering is shown by focused laser irradiation on pristine MoS2 flakes, which are confirmed as catalytic sites by electrodeposition of AuNPs. The preferential Au deposited catalytic sites are found to be electrochemically active for nitrogen adsorption and its subsequent reduction due to the S-vacancies rather than Mo-vacancy, as advocated by DFT analysis. The catalytic performance of Au-NR/MoS2 shows a high yield rate of ammonia (11.43 × 10-8  mol s-1 cm-2 ) at a potential as low as -0.1 V versus RHE and a notable Faradaic efficiency of 13.79% during the electrochemical nitrogen reduction in 0.1 m HCl.

Refining the Spectroscopic Detection Technique: A Pivot in the Electrochemical Ammonia Synthesis.

Ammonia has been recognized as the future fuel because of its immense advantages over liquid hydrogen. The research trend nowadays is mostly inclined toward the electrochemical ammonia synthesis since it offers a sustainable method of green ammonia production. The indophenol blue method is one of the largely used colorimetric techniques to detect ammonia spectroscopically but lacks a proper experimental protocol. The unresolved speculations related to this method concerning stability of dye, sequence of mixing of reagents, importance of pH in the dye formation, or sensitivity of the method to interferants need vigorous experimental verification and a legitimate protocol has to be set up for a reliable and reproducible data. This work thus aims to unveil the artefacts of this method and explore the mechanisms involved such that it becomes easy for a newcomer as well as existing researchers in the field to understand the requirement of rigorous optimizations in this technique.

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis.

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.

Ample Lewis Acidic Sites in Mg2B2O5 Facilitate N2 Electroreduction through Bonding-Antibonding Interactions.

Extensive research on the electrochemical nitrogen reduction reaction (NRR) has put forward a sound list of potential catalyst materials with properties inducing N2 adsorption, protonation, and reduction. However, rather than a random selection of catalysts, it is essential to understand the vitals in terms of orbital orientation and charge distribution that actually manipulate the rate-determining steps of NRR. Realizing these factors, herein we have explored a main group earth-abundant Mg-based electrocatalyst Mg2B2O5 for NRR due to the abundance of Lewis acid sites in the catalyst favoring the bonding-antibonding interactions with the N2 molecules. Positron annihilation studies indicate that the electronic charge distribution within the catalyst has shallow surface oxygen vacancies. These features in the catalyst enabled a sound Faradaic efficiency of 46.4% at -0.1 V vs reversible hydrogen electrode for the selective NH3 production in neutral electrolyte. In situ Fourier transform infrared suggests a maximum N-N bond polarization at -0.1 V and detected H-N-H and -NH2 intermediates during the course of the NRR on the catalyst surface. In a broader picture, the biocompatibility of Mg2+ diversifies the utility of this catalyst material in N2/biofuel cell applications that would certainly offer a green alternative toward our goal of a sustainable society.

Elevating the energy efficiency for the power-to-ammonia conversion: Role of oxygen evolution reaction kinetics.

Electrochemical nitrogen reduction reaction (NRR) is imperatively countered with the oxygen evolution reaction (OER) on a conventional Pt counter electrode. Upon focusing on the development of suitable cathode catalysts, it is usually overseen that OER on Pt seeks a significant energy input to overcome the slow reaction kinetics, regardless of the efficiency of the NRR catalyst. Here, we unveil an out-of-the-box concept with state-of-the-art catalysts that, on pursuing OER with RuO2 in KOH, the NRR process reinforces thermodynamically. In this work, it has been shown how both the electrode and electrolyte simultaneously help to elevate a reaction mechanism in terms of Gibbs' energy and equilibrium constant. As a proof of concept, we assembled RuO2 with an NRR catalyst, iron phthalocyanine (FePc), in an electrolyzer, preferably in a two-electrode setup, where the catholyte consisted of 0.5M NaBF4. This system achieved selective cathodic conversion of N2 to NH3 with 67.6% Faradaic efficiency at 0.0 V (vs reversible hydrogen electrode) and simultaneous anodic water oxidation to O2 with a high electricity-to-chemical energy conversion efficiency of 46.7%. The electrolyzer forecasted a full cell voltage of 2.04 V, which demands only 603 mV overpotential to attain 0.5 mA current to drive forward the chemical equilibrium of the overall cell reaction. This study not only emphasized the importance of electrode-electrolyte improvisation but also provided a wider outlook in terms of different thermodynamic parameters to be considered to determine the efficiency of the overall NRR coupled OER process.

Tuning the Electronic Structure of Cobalt Selenide on Copper Foam by Introducing a Ni Buffer Layer for Highly Efficient Electrochemical Water Splitting.

The development of a cost-effective, remarkably competent, and durable bifunctional electrocatalyst is the foremost requirement of water splitting to generate H2 fuel as a renewable energy technology. Three-dimensional porous copper foam (Cuf) when electrochemically decorated with transition metal selenide results in a highly active electrocatalyst for adequate water electrolysis. In terms of water splitting, the role of cobalt selenide and Cuf has already proven to be remarkable. The introduction of a Ni buffer layer between Cuf and cobalt selenide (Cuf@Ni-CoSe2) acts as a valve to enhance the electron thrust from the substrate to the material surface with no compromise in the overall material conductivity, which not only increases the efficiency and activity but also improves the stability of the catalyst. The self-supported synthesized catalyst material showed an admirable activity toward the oxygen evolution reaction and hydrogen evolution reaction in alkaline media. The performance of the catalyst was found to be significantly better than that of the noble catalyst RuO2. The catalyst was very stable up to 93 h and attained a full cell voltage of only 1.52 V at a current density of 10 mA cm-2. Therefore, for large-scale hydrogen production, this as-synthesized catalyst hss the potential to replace conventional fossil fuel-based energy systems.

Inter-Electronic Interaction between Ni and Mo in Electrodeposited Ni-Mo-P on 3D Copper Foam Enables Hydrogen Evolution Reaction at Low Overpotential.

Electrocatalytic hydrogen evolution reaction (HER) via water electrolysis has been considered the most effective and sustainable route to produce clean hydrogen. Designing and structure optimization are the two important parameters to develop an affordable, easy to fabricate, and stable non-noble metal electrocatalyst for the production of hydrogen as a clean, sustainable, and green fuel. Herein, we have synthesized Ni-Mo-P on copper foam (Cuf) via a facile single-step electrodeposition method, which can show stratospheric efficiency toward HER with a Tafel slope of 67 mV dec-1 and a very low overpotential of only 53 mV at a current density of 20 mA cm-2. Cuf acts as a conducting substrate support and the existence of the inter-electronic effect between Ni and Mo results in substantial catalytic activity toward hydrogen generation. In addition to this, the catalyst shows long time stability of around 97.5 h with almost negligible degradation under the applied overpotential for HER in alkaline media. This work features the significance of structure design and construction of non-noble metal catalysts via a simple method for efficient hydrogen generation.

Polymer-Assisted Electrophoretic Synthesis of N-Doped Graphene-Polypyrrole Demonstrating Oxygen Reduction with Excellent Methanol Crossover Impact and Durability.

The design and synthesis of metal-free catalysts with superior electrocatalytic activity, high durability, low cost, and under mild conditions is extremely desirable but remains challenging. To address this problem, a polymer-assisted electrochemical exfoliation technique of graphite in the presence of an aqueous acidic medium is reported. This simple, cost-effective, and mass-scale production approach could open the possibility for the synthesis of high-quality nitrogen-doped graphene-polypyrrole (NG-PPy). The NG-PPy catalyst displays an improved half wave potential (E1/2 =0.77 V) in alkaline medium compared with G-PPy (E1/2 =0.66 V). Most importantly, this catalyst demonstrates excellent stability with high methanol tolerance, and it outperforms the commercial Pt/C catalyst and other previously reported metal-free catalysts. The content of graphitic nitrogen atoms is the key factor for the enhancement of electrocatalytic activity towards oxygen reduction reactions (ORR). Interestingly, the NG-PPy catalyst can be used as a cathode material in a zinc-air battery, which demonstrates a higher peak power density (59 mW cm-2 ) than G-PPy (36.6 mW cm-2 ), highlighting the importance of the low-cost material synthesis approach towards the development of metal-free efficient ORR catalysts for fuel cell and metal-air battery applications. Remarkably, the polymer-assisted electrophoretic exfoliation of graphite with a high yield (≈88 wt %) of few-layer graphene flakes could pave the way towards the mass production of high-quality graphene for a variety of applications.

Unveiling the Potential of an Fe Bis(terpyridine) Complex for Precise Development of an Fe-N-C Electrocatalyst to Promote the Oxygen Reduction Reaction.

Improvements in highly efficient precious-metal-free electrocatalysts for the oxygen reduction reaction (ORR) are extremely important but still a significant challenge. Herein, we report a novel catalyst design strategy integrating a bis(terpyridine) (hexadentate chelating ligand) with Fe which acts as nitrogen, a self-supporting carbon source, and a potent metal-ligand active site binding structure (Fe-btpy) and promotes the formation of Fe-Nx/C active sites, bypassing the complications induced during Fe-N-C catalyst synthesis. The resulting Fe-N/C(H,P) electrocatalyst shows a very high ORR onset (Eonset) and half-wave potential (E1/2) of 1.05 and 0.89 V (vs reversible hydrogen electrode), respectively, outperforming the commercial Pt/C catalyst in alkaline medium. Most importantly, the Fe-N/C(H,P) catalyst displays decent stability and remarkable methanol tolerance in comparison to the Pt/C catalyst. A fabricated rechargeable zinc-air battery with an Fe-N/C(H,P) cathode catalyst demonstrated an excellent peak power density of 225 mW cm-2 at a current density of 240 mA cm-2, in comparison to the Pt/C cathode catalyst. This work illuminates blueprints utilizing a new long-chain one-dimensional macromolecule that could be viable to produce Fe-N/C-based carbon electrocatalysts toward energy conversion applications.

A No-Sweat Strategy for Graphene-Macrocycle Co-assembled Electrocatalyst toward Oxygen Reduction and Ambient Ammonia Synthesis.

Toward the realm of sustainable energy, the development of efficient methods to enhance the performance of electrocatalysts with molecular level perception has gained immense attention. Inspite of untiring attempts, the production cost and scaling-up issues have been a step back toward the commercialization of the electrocatalysts. Herein, we report a one-pot electrophoretic exfoliation technique with minimum time and power input to synthesize iron phthalocyanine functionalized high-quality graphene sheets (G-FePc). The π-stacked co-assembly excels in oxygen reduction performance (major criterion for fuel cells) with a high positive E1/2 of 0.91 V (vs RHE) and a reproducible reduction peak potential of 0.90 V (vs RHE). An overpotential as low as 29 mV dec-1 and complete tolerance toward the methanol crossover effect confirm the authentication of the catalytic performance of our designed catalyst G-FePc. The catalyst simultaneously exhibits hydrogen storage efficacy by means of nitrogen fixation, yielding 27.74 µg h-1 mgcat-1 NH3 at a potential of -0.3 V (vs RHE) in an acidic electrolyte. The structure-function relationship of the catalyst is revealed via molecular orbital chemistry for the bonding of the Fe(II) active center with O2 and N2 during catalysis.

Unravelling the Role of Fe-Mn Binary Active Sites Electrocatalyst for Efficient Oxygen Reduction Reaction and Rechargeable Zn-Air Batteries.

Transition-metal atoms and/or heteroatom-doped carbon nanostructures is a crucial alternative to find a nonprecious metal catalyst for electrocatalytic oxygen reduction reaction (ORR). Herein, for the first time, we demonstrated the formation of binary (Fe-Mn) active sites in hierarchically porous nanostructure composed of Fe, Mn, and N-doped fish gill derived carbon (Fe,Mn,N-FGC). The Fe,Mn,N-FGC catalyst shows remarkable ORR performance with onset potential (Eonset) of 1.03 V and half-wave potential (E1/2) of 0.89 V, slightly better than commercial Pt/C (Eonset = 1.01 V, E1/2 = 0.88 V) in alkaline medium (pH > 13), which is attributed to the synergistic effect of Fe-Mn dual metal center as evidenced from X-ray absorption spectroscopic study. We proposed that the presence of Fe-Mn binary sites is actually beneficial for the O2 binding and boosting the ORR by weakening the O═O bonds. The homemade rechargeable Zn-air battery performance reveals the open-circuit voltage of 1.41 V and a large power density of 220 mW cm-2 at 260 mA cm-2 current density outperforming Pt/C (1.40 V, 158 mW cm-2) with almost stable charge-discharge voltage plateaus at high current density. The present strategy enriches a route to synthesize low-cost bioinspired electrocatalyst that is comparable to/better than any nonprecious-metal catalysts as well as commercial Pt/C.

Universal Approach for Electronically Tuned Transition-Metal-Doped Graphitic Carbon Nitride as a Conductive Electrode Material for Highly Efficient Oxygen Reduction Reaction.

The rational design of electronically tuned transition-metal-doped conductive carbon nanostructures has emerged as a potential substitution of a platinum-group-metal (PGM)-free electrocatalyst for oxygen reduction reaction (ORR). We report here a universal strategy using a one-step thermal polymerization reaction for transition-metal-doped graphitic carbon nitride (g-C3N4) without any conductive carbon support as a highly efficient ORR electrocatalyst. X-ray absorption spectroscopy evidences the presence of Fe-Nx active sites with a possible three-coordinated Fe atom with N atoms. The as-prepared Fe-g-C3N4 with improved surface area, graphitic nature, and conductive carbon framework exhibits a superior electrochemical performance toward ORR activity in an alkaline medium. Interestingly, it displays a 0.88 V (vs reversible hydrogen electrode, RHE) half-wave potential (E1/2) with a four-electron-transfer pathway and excellent stability outperforming platinum/carbon (Pt/C) in an alkaline medium. More impressively, when the Fe-g-C3N4 catalyst is used as a cathode material in a zinc-air battery, it presents a higher peak power density (148 mW cm-2) than Pt/C (133 mW cm-2), which further established the importance of the low-cost material synthesis approach toward the development of an earth-abundant PGM-free catalyst for fuel-cell and air battery fabrication.

Lewis Acid Mediated Alteration of Electron Density on a Copper Site via pπ-dπ Mixing Enhances the Electrochemical Nitrogen Reduction Reaction.

Strategic modulation of the electronic structure of the catalyst to foster the electrochemical nitrogen reduction reaction (eNRR) to the ammonia process significantly is still an area that needs to be explored. Herein, we report the incorporation of the Lewis acid into an electron-rich copper site regulating the electron density of the metal, which has been experimentally proved from the d-band center position to have a direct influence on the adsorption of N2 compared to the protons. The catalyst boron doped copper-cuprous oxide hybrid system (B-Cu/Cu2O) has shown promising Faradaic efficiency of 32% at -0.2 V vs reversible hydrogen electrode (RHE) compared to the pristine cuprous oxide (Cu2O(N)) system. The in situ Fourier transform infrared study confirms the presence of intermediates evolved during the electroreduction process. This study demonstrates the design of the active center with a specific push-pull interaction via the pπ-dπ bonding-antibonding approach and can shed light on the electrochemical activation and reduction of dinitrogen to produce ammonia.

Strategic design of VO2 encased in N-doped carbon as an efficient electrocatalyst for the nitrogen reduction reaction in neutral and acidic media.

Electrocatalytic nitrogen fixation to ammonia (NH3), a precursor for fertilizer production and a promising energy carrier, has garnered widespread interest as an environment-friendly and sustainable alternative to the energy-intensive fossil-feedstock-dependent Haber-Bosch process. The large-scale deployment of this process is contingent on the identification of inexpensive, Earth-abundant systems that can operate efficiently, irrespective of the electrolyte pH for the selective production of NH3. In this regard, we discuss the scalable synthesis of VO2 anchored on N-doped carbon (VO2@CN), and its applicability as a robust electrocatalyst for the nitrogen reduction reaction (NRR). Benefitting from the presence of exposed VO2, which presumably acts as the active site for nitrogen reduction, and its activity over a broad pH range (from acidic to neutral), VO2@CN exhibits a high NH3 yield of 0.31 and 0.52 µmol h-1 mgcat-1 and a maximum Faradaic efficiency (FE) of 67.9% and 61.9% at -0.1 V vs. RHE, under neutral and acidic conditions, respectively. The obscured reaction intermediates of the NRR were identified from in situ ATR-IR studies under both electrolyte conditions. Additionally, the high selectivity of the catalyst was ascertained from the absence of hydrazine production and the competing hydrogen evolution reaction (HER). However, ammonia production underwent a reduction over 12 h of continuous operation presumably owing to the leaching of catalyst under these electrolysis conditions, which was more pronounced in electrolytes with acidic pH. Overall, the present report unveils the performance of an earth-abundant vanadium oxide-based system as an efficient electrocatalyst for the NRR under acidic and neutral pH conditions.

Deciphering the bridge oxygen vacancy-induced cascading charge effect for electrochemical ammonia synthesis.

Oxygen vacancy engineering has recently been gaining much interest as the charging effect it induces in a material can be used for varied applications. Usually, semiconductor materials act poorly in electrocatalysis, particularly in the nitrogen reduction reaction (NRR), owing to their inherent charge deficit and huge band gap. Vacancy introduction can be a viable material engineering route to make use of these materials for the NRR. However, a detailed investigation of the vacancy-type and its role for the structural reorientation and charge redistribution of a material is lagging in the field of NRRs. This work thus focuses on the synthesis of oxygen vacancy-engineered SnO2 with a gradual structural transformation from in-plane (iov) to bridge-type oxygen vacancy (bov) density. Consequently, the electron occupancy of the sp3d hybrid orbital changes, leading to an upshifted valence band maxima towards the Fermi level. This has a profound effect on the nature of N2 adsorption and the extent of NN bond polarization. Sn atoms adjacent to the bov are found to have a fair density of dangling charges that accomplish the NRR process at a comparatively low overpotential and determine the binding strength of the intermediates on the active site. The obscured yet stable reaction intermediates are thereby identified with in situ ATR-IR studies. A restricted hydrogen evolution reaction Faradaic on the Sn-site (favored over O-atoms) results in a Faradaic efficiency of 48.5%, which is better than that reported in all the literature reports on SnO2 for the NRR. This study thus unveils sufficient insights into the role of oxygen vacancies in a crystal as well as electronic structural alteration of SnO2 and the effect of active sites on the rate kinetics of the NRR.

Nanomaterial-based functional scaffolds for amperometric sensing of bioanalytes.

Functional nanomaterials have emerged as promising candidates in the development of an amperometric sensing platform for the detection and quantification of bioanalytes. The remarkable characteristics of nanomaterials based on metal and metal oxide nanoparticles, carbon nanotubes, and graphene ensure enhanced performance of the sensors in terms of sensitivity, selectivity, detection limit, response time, and multiplexing capability. The electrocatalytic properties of these functional materials can be combined with the biocatalytic activity of redox enzymes to develop integrated biosensing platforms. Highly sensitive and stable miniaturized amperometric sensors have been developed by integrating the nanomaterials and biocatalyst with the transducers. This review provides an update on recent progress in the development of amperometric sensors/biosensors using functional nanomaterials for the sensing of clinically important metabolites such as glucose, cholesterol, lactate, and glutamate, immunosensing of cancer biomarkers, and genosensing.

Laser-irradiated carbonized polyaniline-N-doped graphene heterostructure improves the cyclability of on-chip microsupercapacitor.

Laser-irradiated graphene-based heterostructures have attracted significant attention for the fabrication of highly conducting and stable metal-free energy storage devices. Heteroatom doping on the graphene backbone has proven to have better charge storage properties. Among other heteroatoms, nitrogen-doped graphene (NG) has been extensively researched due to its several advanced properties while maintaining the original characteristics of graphene for energy storage applications. However, NG is generally prepared via chemical vapor deposition or high temperature pyrolysis method, which gives low yield and has a complex operation route. In this work, first a polyaniline-reduce graphene oxide (PANI-rGO) heterostructure was prepared via in situ electrochemical polymerization, followed by the deposition process. In the next step, laser-irradiation process was employed to carbonize polyaniline as well as doping of nitrogen on the graphene film, simultaneously. For the very first time, laser-irradiated carbonization of PANI on NG (cPANI-NG) heterostructure was utilized for microsupercapacitor (MSC). The as-prepared cPANI-NG-MSC shows extremely high cycling stability with a capacitance enhancement of 135% of its initial capacitance after 70 000 continuous charge-discharge cycles. It is very interesting to know the origin of the capacitance enhancement, which results from the change of pyrrolic N in NG-MSC to the pyridinic and graphitic N. An on-chip NG-MSC exhibits an excellent charge storage capacitance of 43.5 mF cm-2 at a current density of 0.5 mA cm-2 and shows impressive power delivery at a very high scan rate of 100 V s-1. The excellent rate capability of the MSC shows capacitance retention up to 70.1% with the variation of current density. This unique approach to fabricate NG-MSC can have a broad range of applications as energy storage devices in the electronics market, as demonstrated by glowing a commercial red LED.