Sambhaji S. Shinde

Scalable 3-D Carbon Nitride Sponge as an Efficient Metal-Free Bifunctional Oxygen Electrocatalyst for Rechargeable Zn–Air Batteries

Rational design of efficient and durable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is critical for rechargeable metal-air batteries. Here, we developed a facile strategy for fabricating three-dimensional phosphorus and sulfur codoped carbon nitride sponges sandwiched with carbon nanocrystals (P,S-CNS). These materials exhibited high surface area and superior ORR and OER bifunctional catalytic activities than those of Pt/C and RuO2, respectively, concerning its limiting current density and onset potential. Further, we tested the suitability and durability of P,S-CNS as the oxygen cathode for primary and rechargeable Zn-air batteries. The resulting primary Zn-air battery exhibited a high open-circuit voltage of 1.51 V, a high discharge peak power density of 198 mW cm-2, a specific capacity of 830 mA h g-1, and better durability for 210 h after mechanical recharging. An extraordinary small charge-discharge voltage polarization (∼0.80 V at 25 mA cm-2), superior reversibility, and stability exceeding prolonged charge-discharge cycles have been attained in rechargeable Zn-air batteries with a three-electrode system. The origin of the electrocatalytic activity of P,S-CNS was elucidated by density functional theory analysis for both oxygen reactions. This work stimulates an innovative prospect for the enrichment of rechargeable Zn-air battery viable for commercial applications such as armamentaria, smart electronics, and electric vehicles.

Electrocatalytic hydrogen evolution using graphitic carbon nitride coupled with nanoporous graphene co-doped by S and Se†

Electrocatalytic hydrogen evolution using non-precious metals or metal-free catalysts is critically necessary because platinum-based electrocatalysts are greatly limited in scalable commercialization of hydrogen generation due to their high cost. Here, we report the facile synthesis of metal-free hybrid catalysts, in which graphitic carbon nitride (g-C3N4) is coupled with nanoporous graphene doped by S and Se. The S and Se co-doped hybrid catalyst (g-C3N4@S–Se-pGr) reveals superior electrocatalytic performances, including an exchange current density of 6.27 × 10−6 A cm−2, an on-set potential of 0.092 V, a Tafel slope of 86 mV dec−1, an adsorption free energy of −0.13 eV, and long-term stability comparable to those of commercial Pt/C catalysts. Volcano plots showing the hydrogen evolution activity versus adsorption free energy are also compatible with those of the conventional metal catalysts. Our strategy has the potential to allow a new paradigm for the development of high-performance metal-free electrocatalysts for energy conversion devices.

Nitrogen‐ and Phosphorus‐Doped Nanoporous Graphene/Graphitic Carbon Nitride Hybrids as Efficient Electrocatalysts for Hydrogen Evolution

The hydrogen evolution reaction (HER) is one of the key steps in clean and efficient energy conversion techniques; however, the mass production of current HER devices is hampered by several shortcomings, which include kinetically sluggish processes, stability, and the use of expensive catalysts. In this work we report the facile synthesis of metal‐free hybrids by integrating graphitic carbon nitride (g‐C3N4) with nitrogen‐ and phosphorus‐doped nanoporous graphene sheets. A phosphorus‐doped metal‐free hybrid electrocatalyst (g‐C3N4@P‐pGr) displayed excellent HER performance with an overpotential of −0.34 V, high exchange current density of 3.33×10−6 A cm−2, onset potential of 0.076 V, Tafel slope of 90 mV dec−1, Gibbs free energy of −0.16 eV, and long‐term durability comparable to that of well‐developed metal catalysts. Tafel slope analysis suggests that the Volmer–Tafel mechanism is the most favorable HER kinetics for these metal‐free hybrids. The extraordinary HER performance stems from a strong synergistic effect between the highly exposed active sites generated by the introduction of in‐plane pores into graphene and the coupling of g‐C3N4.

In situ directional formation of Co@CoOx-embedded 1D carbon nanotubes as an efficient oxygen electrocatalyst for ultra-high rate Zn–air batteries

In this work, we demonstrate a “three birds one stone” strategy for preparing 1D N-doped porous carbon nanotubes embedded with core–shell Co@CoOx nanoparticles (Co@CoOx/NCNTs) from bimetallic ZnO@Zn/Co-ZIF nanowires. The ZnO nanowires played three roles: (i) ZnO acted as a template for 1D metal–organic framework (MOF) growth, (ii) in situ evaporation of Zn during pyrolysis prevented the aggregation of the carbon framework and benefited the formation of hierarchical pores, and (iii) the excess oxygen species released from ZnO in situ reacted with metallic cobalt nanoparticles during pyrolysis, leading to the configuration of a Co@CoOx core–shell structure. The as-prepared 1D Co@CoOx/NCNTs exhibited excellent oxygen reduction reaction performance, including a high kinetic current (4.6 times better compared to 20 wt% Pt/C at 0.7 V), a low Tafel slope of 80 mV dec−1, outstanding stability, and strong tolerance to CH3OH crossover. The assembled Zn–air batteries with Co@CoOx/NCNTs yielded high open-circuit voltage (1.52 V), superior stability (over 100 h of operation), and unprecedented rate performance that ranged from 1 to 500 mA cm−2, while existing batteries have never achieved a galvanostatic discharge current density larger than 300 mA cm−2. Such exceptional rate capability was ascribed to the formation of a uniform interconnected nanotube network, facilitated electron transport, and an enlarged electrochemically accessible surface area in the unique 1D porous tubular structure.

Highly active and durable carbon nitride fibers as metal-free bifunctional oxygen electrodes for flexible Zn–air batteries

The design of flexible, highly energetic, and durable bifunctional oxygen electrocatalysts is indispensable for rechargeable metal-air batteries. Herein we present a simple approach for the development of carbon nitride fibers co-doped with phosphorus and sulfur, grown in situ on carbon cloth (PS-CNFs) as a flexible electrode material, and demonstrate its outstanding bifunctional catalytic activities toward ORR and OER compared to those of precious metal-based Pt/C and IrO2 on account of the dual action of P and S, numerous active sites, high surface area, and enhanced charge transfer. Furthermore, we demonstrate the flexibility, suitability, and durability of PS-CNFs as air electrodes for primary and rechargeable Zn-air batteries. Primary Zn-air batteries using this electrode showed high peak power density (231 mW cm-2), specific capacity (698 mA h g-1; analogous energy density of 785 W h kg-1), open circuit potential (1.49 V), and outstanding durability of more than 240 h of operation followed by mechanical recharging. Significantly, three-electrode rechargeable Zn-air batteries revealed a superior charge-discharge voltage polarization of ∼0.82 V at 20 mA cm-2, exceptional reversibility, and continuous charge-discharge cycling stability during 600 cycles. This work provides a pioneering strategy for designing flexible and stretchable metal-free bifunctional catalysts as gas diffusion layers for future portable and wearable renewable energy conversion and storage devices.

Flexible and rechargeable Zn–air batteries based on green feedstocks with 75% round-trip efficiency

Here, we report a flexible solid-state Zn–air battery (SZAB) that achieves a record round-trip efficiency of 75%. The major components of the SZAB are based on biomass derivatives. Glucose acts as the carbon source to construct the bifunctional oxygen electrocatalyst. Methylcellulose simultaneously enhances the ionic conductivity and water retention of the gel electrolyte, endowing the SZAB with enhanced flexibility and efficiency.

Hierarchically Designed 3D Holey C2N Aerogels as Bifunctional Oxygen Electrodes for Flexible and Rechargeable Zn-Air Batteries

The future of electrochemical energy storage spotlights on the designed formation of highly efficient and robust bifunctional oxygen electrocatalysts that facilitate advanced rechargeable metal-air batteries. We introduce a scalable facile strategy for the construction of a hierarchical three-dimensional sulfur-modulated holey C2N aerogels (S-C2NA) as bifunctional catalysts for Zn-air and Li-O2 batteries. The S-C2NA exhibited ultrahigh surface area (∼1943 m2 g-1) and superb electrocatalytic activities with lowest reversible oxygen electrode index ∼0.65 V, outperforms the highly active bifunctional and commercial (Pt/C and RuO2) catalysts. Density functional theory and experimental results reveal that the favorable electronic structure and atomic coordination of holey C-N skeleton enable the reversible oxygen reactions. The resulting Zn-air batteries with liquid electrolytes and the solid-state batteries with S-C2NA air cathodes exhibit superb energy densities (958 and 862 Wh kg-1), low charge-discharge polarizations, excellent reversibility, and ultralong cycling lives (750 and 460 h) than the commercial Pt/C+RuO2 catalysts, respectively. Notably, Li-O2 batteries with S-C2NA demonstrated an outstanding specific capacity of ∼648.7 mA h g-1 and reversible charge-discharge potentials over 200 cycles, illustrating great potential for commercial next-generation rechargeable power sources of flexible electronics.

Solid-State Rechargeable Zinc-Air Battery with Long Shelf Life Based on Nanoengineered Polymer Electrolyte

Zinc-air batteries (ZABs) are vulnerable to the ambient environment (e.g., humidity and CO2 ), and have serious selfdischarge issues, resulting in a short shelf life. To overcome these challenges, a near-neutral quaternary ammonium (QA) functionalized polyvinyl alcohol electrolyte membrane (different from conventional alkali-type membranes) has been developed. QA functionalization leads to the formation of interconnected nanochannels by creating hydrophilic/-phobic separations at the nanoscale. These nanochannels selectively transport OH- ions with a reduced migration barrier, while inhibiting [Zn(NH3 )6 ]2+ crossover. Owing to the superior water retention ability and enhanced chemical stability of the membrane, the solid-state zinc-air battery (SZAB) displays outstanding flexibility, a promising cycle lifetime, and a large volumetric energy density. More importantly, the self-discharge rate of SZAB is depressed to less than 7 % per month, and the fully dehydrated SZAB could recover its rechargeability upon replenishment of the solution of NH4 Cl.

Planar n-Si/PEDOT:PSS hybrid heterojunction solar cells utilizing functionalized carbon nanoparticles synthesized via simple pyrolysis route.

Herein, we present a facile and simple strategy for in situ synthesis of functionalized carbon nanoparticles (CNPs) via direct pyrolysis of ethylenediaminetetraacetic acid (EDTA) on silicon surface. The CNPs were incorporated in hybrid planar n-Si and poly(3,4-etyhlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells to improve device performance. We demonstrate that the CNPs-incorporated devices showed increased electrical conductivity (reduced series resistance) and minority carrier lifetime (better charge carrier collection) than those of the cells without CNPs due to the existence of electrically conductive sp 2-hybridized carbon at the heterojunction interfaces. With an optimal concentration of CNPs, the hybrid solar cells exhibited power conversion efficiency up to 11.95%, with an open-circuit voltage of 614 mV, short-circuit current density of 26.34 mA cm-2, and fill factor of 73.93%. These results indicate that our approach is promising for the development of highly efficient organic-inorganic hybrid solar cells.