A novel vertical non-van der Waals (non-vdW) heterostructure of graphene and hexagonal boron nitride (G/hBN) is realized and its application in direct four-electron oxygen reduction reaction (ORR) in alkaline medium is established.

sectors, such as in high energy density demand portable devices, solar vehicles, solar impulse planes, satellites, etc. [4][5][6] This concept was initially proposed by Hodes et al. in 1976, where they have shown a three-electrode system comprised of cadmium selenide, sulfur, and silver sulfide (CdSe/S/Ag 2 S). [7] In this system, one of the components acted as photoelectrode while the others acted as the components for the energy storage. Such efforts have continued with other threeelectrode systems, such as n-cadmium selenide telluride/cesium sulfide/tin sulfide [8] and hybrid titania (TiO 2 ) poly(3,4ethylenedioxythiophene) as photo anode and a perchlorate (ClO 4 − )-doped polypyrroles counter electrode. This approach was improved by using a two-electrode system with a hybrid mixture of lithium iron phosphate (LFP) nanocrystals and N719 dye as the active photo-electrode assembled with lithium metal as counter electrode. [9] The N719 dye acts as photon absorber and lithium iron phosphate (LFP) as cathode. In this system, during the photocharging, the electrons produced during the photo-excitation of the dye generate holes in the valance band which repel Li-ions from their intercalated state. The continuous photo-conversion drives the battery to reach back in the charged state (in 30 h) with a 200 W solar spectrum (simulator). [9] It has low photo conversion efficiency and it was observed that soon after the first cycle, the charge capacity started fading due to dissolution of the organic dye in to the organic electrolyte.A different approach was attempted later, where a polycrystalline metal halide based 2D perovskite was used as a photoactive electrode ((C 6 H 9 C 2 H 4 NH 3 ) 2 PbI 4 ) that could provide both energy storage (battery functionality) and photo charging (photovoltaic functionality). [10] This perovskite system provided a low photo conversion efficiency of ≈0.034%. Furthermore, the system suffered from various other challenges such as the conversion reaction between lithium and perovskite generating lead (Pb), where it can further alloy with lithium causing a large volume expansion.More recently, it was reported that an organic molecule based photo-electrode could also be used for photo charging. [11] Absorption of light of a desired wavelength by lithiatedtetrakislawsone electrodes generates electron-hole pairs, and the holes oxidize the lithiated-tetrakislawsone to tetrakislawsone while the generated electrons flow from the tetrakislawsone New ways of directly using solar energy to charge electrochemical energy storage devices such as batteries would lead to exciting developments in energy technologies. Here, a two-electrode photo rechargeable Li-ion battery is demonstrated using nanorod of type II semiconductor heterostructures with in-plane domains of crystalline MoS 2 and amorphous MoO x . The staggered energy band alignment of MoS 2 and MoO x limits the electron holes recombination and causes holes to be retained in the Li intercalated MoS 2 electrode. The holes generated in the MoS 2 pushes...

The surface modification of benchmarked metal catalysts using nanostructured non‐metallic materials for improved performance and stability is an active area of research and is interesting from both a fundamental and an applied perspective. Amorphous few layered nanosheets of Cr2O3 (3–5 nm) are synthesized by rapid thermal exfoliation of CrCl3 · 6H2O precursors and are characterized. The hydrogen evolution reaction (HER) studies on alkaline medium conducted with platinum and gold electrodes modified with amorphous sheets of Cr2O3 show augmented HER activity compared to the pristine ones while Cr2O3 alone is not HER active. The role of amorphous Cr2O3 as a co‐catalyst is established and the synergistic charge transfer effects while coupling Cr2O3 with metal catalysts are studied using electrochemical impedance spectroscopy. Large‐scale processability of amorphous Cr2O3 by rapid thermal treatment along with its high electrochemical stability (>2000 cycles or >50 h) in harsh alkaline conditions, where benchmarked metals fail, open new avenues in designing novel scalable catalysts by protecting the surface of noble metal catalysts without sacrificing the electrochemical performance.

Tweaking the electrolyte of the anode compartment of zinc−air battery (ZAB) system is shown to be extending the charge−discharge cyclability of the cell. An alkaline zinc (Zn)− air cell working for ∼32 h (192 cycles) without failure is extended to >55 h (>330 cycles) by modifying the anode compartment with a mixture electrolyte of KOH and LiOH. The cell containing the mixture electrolyte has a low overpotential for charging along with high discharge capacity. The role of Li + ions in tuning the electrode morphology and electrodics is studied both theoretically and experimentally. The synergistic effect of Li + and K + ions in the electrolyte on improved ZAB performance is proven. This study can pave new ways for the commercial implementation of ZAB, where it has already proven its potential in low-cost, high energy density, and mobility applications.

The studies shown here prove that both the Li salt and ‘inert-polymer’ mixing have paramount importance in the tunability of Li ion conductivity in solid electrolytes for batteries.

The zinc−air battery (ZAB) is an emerging rechargeable energy storage system having high energy density (1084 Wh/kg) with safe operation and low operation cost (∼$10 kW/h). Development of a durable and efficient bifunctional catalyst is the bottleneck of rechargeable ZAB technology, and here we demonstrate a hybrid catalyst system having cobalt (Co) nanoparticles dispersed graphitic spheres as an efficient catalyst at the air electrodeperforming better than the benchmarked ones while constructing the ZAB cells. Co nanoparticles dispersed nitrogendoped graphitic nanospheres (Co@NGC-NSs) were developed using a unique synthesis strategy, and it showed excellent bifunctional catalytic activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. The potential difference calculated with Co@NGC-NSs, considering the potential for the current density of 10 mAcm −2 for OER and current density corresponding to the half wave potential for ORR, is found to be (0.78 V) lower than that of Pt/C and IrO 2 (0.87 V) system. The zinc−air cell constructed using Co@NGC-NSs shows an open circuit voltage of 1.36 V having a maximum power density of ∼52 mW cm −2 and an energy density of 876 Wh/kg, and these values are on par with the Pt/C system while much better in terms of long-term stable performance where Pt/C is found to be failing. A detailed comparison with the reported performance of other catalyst-based ZABs indicates that the Co@NGC-NSs-based ZABs has high potential as a practically viable system, where the catalyst development is also found to be simple and nonexpensive in nature.

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Metal phosphorus trichalcogenide (MPX3) materials have aroused substantial curiosity in the evolution of electrochemical storage devices due to their environment-friendliness and advantageous X-P synergic effects. The interesting intercalation properties generated due to the presence of wide van der Waals gaps along with high theoretical specific capacity pose MPX3 as a potential host electrode in lithium batteries. Herein, we synthesized two-dimensional iron thio-phosphate (FePS3) nanoflakes via a salt-template synthesis method, using low-temperature time synthesis conditions in single step. The electrochemical application of FePS3 has been explored through the construction of a high-capacity lithium primary battery (LPB) coin cell with FePS3 nanoflakes as the cathode. The galvanostatic discharge studies on the assembled LPB exhibit a high specific capacity of ~1791 mAh g−1 and high energy density of ~2500 Wh Kg−1 along with a power density of ~5226 W Kg−1, some of the highest reported values, indicating FePS3’s potential in low-cost primary batteries. A mechanistic insight into the observed three-staged discharge mechanism of the FePS3-based primary cell resulting in the high capacity is provided, and the findings are supported via post-mortem analyses at the electrode scale, using both electrochemical- as well as photoelectron spectroscopy-based studies.