Doped MXenes—A new paradigm in 2D systems: Synthesis, properties and applications

Since 2011, 2D transition metal carbides, carbonitrides and nitrides known as MXenes have gained huge attention due to their attractive chemical and electronic properties. The diverse functionalities of MXenes make them a promising candidate for multitude of applications. Recently, doping MXene with metallic and non-metallic elements has emerged as an exciting new approach to endow new properties to this 2D systems, opening a new paradigm of theoretical and experimental studies. In this review, we present a comprehensive overview on the recent progress in this emerging field of doped MXenes. We compare the different doping strategies; techniques used for their characterization and discuss the enhanced properties. The distinct advantages of doping in applications such as electrocatalysis, energy storage, photovoltaics, electronics, photonics, environmental remediation, sensors, and biomedical applications is elaborated. Additionally, theoretical developments in the field of electrocatalysis, energy storage, photovoltaics, and electronics are explored to provide key specific advantages of doping along with the underlying mechanisms. Lastly, we present the advantages and challenges of doped MXenes to take this thriving field forward

Doped MXenes—A new paradigm in 2D systems: Synthesis, properties and applications

Since 2011, 2D transition metal carbides, carbonitrides and nitrides known as MXenes have gained huge attention due to their attractive chemical and electronic properties. The diverse functionalities of MXenes make them a promising candidate for multitude of applications. Recently, doping MXene with metallic and non-metallic elements has emerged as an exciting new approach to endow new properties to this 2D systems, opening a new paradigm of theoretical and experimental studies. In this review, we present a comprehensive overview on the recent progress in this emerging field of doped MXenes. We compare the different doping strategies; techniques used for their characterization and discuss the enhanced properties. The distinct advantages of doping in applications such as electrocatalysis, energy storage, photovoltaics, electronics, photonics, environmental remediation, sensors, and biomedical applications is elaborated. Additionally, theoretical developments in the field of electrocatalysis, energy storage, photovoltaics, and electronics are explored to provide key specific advantages of doping along with the underlying mechanisms. Lastly, we present the advantages and challenges of doped MXenes to take this thriving field forward

Development of High Performance Lead-Acid Batteries through Electrode and Electrolyte Additives

Over the last few decades’ energy has become the central focus of the modern economy. Energy security and efficiency has become a national priority. The access to energy is very critical to the wealth, life style and image of every country. The effect of globalization, population increase and rising consumer demands across the developed and developing countries have resulted in an exponential increase in energy consumption. This has significantly increased the gap between energy production and demand over the last few decades. Fundamental breakthrough in clean energy research is needed to solve the problem of such magnitude. Innovations in materials and processing technology provide significant opportunities for transitioning from fossil based sources to clean energy sources such as nuclear, wind and solar energy. Renewable energy sources like solar and wind provides time-varying (depend on climatic conditions), somewhat unpredictable energy supply, which must be captured and stored until demanded. Success of these technologies relies on development of efficient energy storage materials that can be utilized in smart batteries and capacitors. Fuel cells offer another alternative clean energy but would probably require further research in bringing down the cost for mass market. India's is a fast growing economy and its prime agenda is transformation of reducing energy demand, improving its efficiency, increased use of renewable energy sources for power and transportation. Key to this mission is transport ministry has announced 30% electric mobility by 2030 and Energy ministry targets 225 GW of renewable energy by year 2022. Although there are encouraging progresses in the development of technology for harvesting sustainable energy from different sources, the development of energy storage devices with desirable properties such as long-term stability, prolonged cycle life and cost are still lagging far behind. The shifting of road transportation from vehicles driven by internal combustion engines (ICE) to electric vehicles (EVs) or Hybrid Electric Vehicles (HEVs), a real ‘green’ revolution also requires efficient energy storage systems. The electrochemical energy storage in batteries have been attained much interest due to their compactness, life, ease installations, availability and low cost. Although many battery technologies are available in the market today, lead-acid batteries continue to be one of the most popular battery system ever developed, and no other battery is yet able to compete with the lead-acid batteries on cost grounds. Lead-acid batteries remain the most successful energy storage device in automotive, telecommunication, uninterruptible power supplies [1-4]. Even though lead-acid batteries performances are optimized in the past in several different ways, there are still certain challenges facing lead-acid battery designers, as additional failure modes become evident in various end-uses. The life of lead-acid batteries is limited due to grid corrosion at the positive plate and sulfation at the negative plates during storage and heavy-duty operations [5-9]

Carbon Coated SnO2 as a Negative Electrode Additive for High Performance Lead Acid Batteries and Supercapacitors

Sulfation at the negative electrode and grid corrosion at the positive electrode are the major failure modes of lead-acid batteries. To overcome the issues of sulfation, we synthesize carbon coating onto SnO2 as a negative electrode additive for lead-acid batteries. 0.25 wt% of carbon-SnO2 additive into the negative active material reduces formation cycle from 3 cycles to 1 cycle and 60% increment in capacity during the 1st cycle compare to conventional lead-acid cell. The additive cells also deliver 300 deep charge-discharge cycles at C/5 rate and >60% increase in capacity at 2C rate in relation to conventional lead-acid cells. The enhancement in capacity at all C rates and improvement in cycling is due to carbon coating which enhances the conductivity and charge storage property of negative active material. Carbon-SnO2 occupies in the pores of negative active material, restricts the growth of PbSO4 and decreases hydrogen evolution, thereby improves charge acceptance. Besides, the additive cells show 300% increase in high rate partial state of charge cycles compare to conventional lead-acid cells. The specific capacitance of carbon coated SnO2 in 4.5 M H2SO4 is 150 F g−1, at 2A g−1 with >90% capacity retention after 2000 cycles

Boron, Nitrogen-Doped Porous Carbon Derived from Biowaste Orange Peel as Negative Electrode Material for Lead-Carbon Hybrid Ultracapacitors

Lead-Carbon hybrid ultracapacitors have attracted attention in recent times due to high power density and remarkably long cycling stability. Herein, we report bio-waste orange peel derived B, N doped porous carbons as negative electrode active material for Pb-C hybrid ultracapacitors. B, N doped porous carbons are obtained from orange peel using boric acid by carbonization at 800 °C. B, N doped porous carbons contain about 1.22% of boron, 2.89% of nitrogen. These porous carbons exhibit 866 F g−1 capacitance at 1 A g−1 current density in potential range between the −0.4 V to 0.2 V. Pb-C hybrid ultracapacitors assembled with these carbons as the negative electrode and in situ formed PbO2 as a positive electrode can deliver capacitance of 192 F g−1 at 10 A g−1 and stable over 10,000 cycles. The superior electrochemical performance of lead-carbon ultracapacitor is due to the boron and nitrogen doping into the carbon, which increases the hole density and electron carrier, respectively and subsequently enhances the charge storage property. The significant improvement in capacitance of the ultracapacitor electrode of Pb-C hybrid ultracapacitors presented here opens up a new realm of possibilities for the lead-carbon ultracapacitor development and will contribute directly towards improving the energy and power density of the system

Poly(3,4-ethylenedioxythiophene) coated lead negative plates for hybrid energy storage systems

Herein, we report Poly(3,4-ethylenedioxythiophene) coating on to lead negative plates as a hybrid electrode material for lead-acid batteries and supercapacitors. Poly(3,4-ethylenedioxythiophene) coating on to negative plate addresses the issue of sulfation at negative plate in a lead-acid cell. Poly(3,4-ethylenedioxythiophene) coating on to the conventional negative plates is wind up by electropolymerization technique. 2 V/2.1 A h lead-acid cells assemble with Poly(3,4-ethylenedioxythiophene) coating negative electrodes show ∼25% increase in initial discharge capacity, excellent cycle performance at 5 h rate, lower impedance, reduce hydrogen evolution and boost charge acceptance in relation to the conventional lead-acid cell. The Poly(3,4-ethylenedioxythiophene) coating lead-acid cells show 20% improvement in C/5 rate and 107% in high rate partial state of charge cycling. The specific capacitance of Poly(3,4-ethylenedioxythiophene) in 4.5 M H2SO4 medium is about 105 F g−1 with an excellent cycle life of over 20, 000 cycles at 2 A g−1. The superior performance is due to fast kinetics of Poly(3,4-ethylenedioxythiophene) in sulfuric acid electrolyte

Boron doped graphene nanosheets as negative electrode additive for high-performance lead-acid batteries and ultracapacitors

Sulfation at the negative electrode is one of the major failure modes of lead-acid batteries. To overcome the issues of sulfation, in this work we synthesize Boron doped graphene nanosheets as an efficient negative electrode additive for lead-acid batteries. 0.25 wt % Boron doped graphene nanosheets additive in negative electrode which contains around 3% of Boron doping shows impressive electrochemical performance in first discharge capacity, ∼60% increase the capacity in relation to the conventional lead-acid cell. Noticeably, 15–20% enhancement in the discharge capacity at lower C rates and almost double increase in capacity at higher C rates show Boron doped graphene nanosheets as a potential additive for lead-acid battery operating under high rate partial state of charge applications. The superior electrochemical performance is due to the p-type or hole conductivity of the Boron doped graphene lattice, which reduces lead sulfate formation and thereby enhances active material utilization, charge acceptance, and reduces hydrogen evolution. Besides, the high C-rate performance of Boron doped graphene nanosheets additive cell is due to the capacitive property of Boron-doped graphene nanosheets which delivers specific capacitance of 90 F g−1 at 2 A g−1 with >75% capacity retention at the end of 2000 cycles

Charge storage behavior of sugar derived carbon/MnO2 composite electrode material for high-performance supercapacitors

Herein, we present an efficient and simple method to develop a 3D-Carbon /MnO2 (C/MnO2) composite active material for high-performance supercapacitors. MnO2 nanorods are synthesized by the hydrothermal process, and corresponding carbon composite is synthesized from table sugar precursors using the combustion process. MnO2 has rod-like morphologies and forms 3D electrode architectures with carbon, and contains about 5–10 nm of carbon coating. The charge storage behavior studied by galvanostatic charge-discharge cycling shows capacitance of 416 F g−1 at 1 A g−1 with capacitance retention of 90% after 5000 cycles. The superior electrochemical performance is attributed to the one–dimensional ion transport of Mn ion, the in-situ 3D electrode architecture, and carbon coating that enhances the conductivity and the surface area of MnO2. C/MnO2 composite exhibits an energy density of 60 Wh kg−1 with a power density of 201 W kg−1. The combined pseudocapacitive behavior of MnO2 and electric double-layer capacitors property of carbon exhibits significant electrochemical performance in the aqueous electrolyte. The synthesis approach uses environment benign active materials with the low cost of electrode fabrication provides an alternative route for the development of high-performance supercapacitors. © 2021 Elsevier B.V

Corrosion Resistant Polypyrrole Coated Lead-Alloy Positive Grids for Advanced Lead-Acid Batteries

We herein report a method for reducing lead-alloy positive grid corrosion in lead acid batteries by developing a polypyrrole (ppy) coating on to the surface of lead-alloy grids through potentiostatic polymerization technique. The experimental results demonstrate that the presence of ppy coating significantly enhances the corrosion resistance and inhibits the oxygen evolution rate as compare to bare grids. C-rate studies of 2 V/2.6 Ah lead-acid cells show ∼15–20% improvement in capacity at low charge-discharge rates (C/20- C/5) and ∼10% at high C rates (C/2 and 3C) for the cells with ppy coating grids in relation to conventional lead-acid cells

Microwave aided scalable synthesis of sulfur, nitrogen co-doped few-layered graphene material for high-performance supercapacitors

Doping with heteroatoms has become an approach for improving the electrochemical performance of few-layered graphene. In this work, Sulfur-nitrogen co-doped few-layered graphene synthesized from the graphite flakes acid treated with H2SO4 and HNO3 followed by microwave irradiation. Sulfur-nitrogen co-doped few-layered graphene consists of less than 15 graphene layers with a high degree of graphitization. The supercapacitor exhibited a specific energy density of 15 Wh kg−1 at a power density of 300 W kg−1at room temperature in aqueous electrolyte. The S, N-FLG electrodes show the specific capacitance of 298 F g−1 at a current density of 1 A g−1and stable over 10,000 continuous charge-discharge cycles with 95% capacitance retention at 1 A g−1. The obtained capacitance is due to maximum utilization of few-layered graphene sheets, highest intrinsic surface capacitance due to the synergetic effect of the formation of N-S-H hydrogen bonds and S, N co-doping in graphene aromatic rings