Decavanadate Doped Polyaniline for Aqueous Zinc Batteries.

Polyaniline (PANI) is a promising cathode material for aqueous rechargeable zinc batteries (ARZBs), mainly benefitting from its good electrical conductivity. The high conductivity of PANI requires high doping level, yet the introduced nonactive dopants (e.g., SO4 2- ) limit the gravimetric capacity of PANI (usually < 180 mAh g-1 ). Herein, an electro-active dopant (decavanadate anion, V10 O28 6- ) is employed to fabricate the PANI cathode (PANI-V10 O28 ) for ARZBs. The doped decavanadate anion with the sub-nanometer structure can fully expose the V-based active sites, exhibiting good electrochemical activity. Due to the steric hindrance effect as well as the strong interaction between decavanadate anions and PANI chains, the active dopants are trapped in the polymer chains, demonstrating good structural and electrochemical stability. PANI-V10 O28 achieves a record-high gravimetric capacity of 355 mAh g-1 at 0.1 A g-1 , which is significantly higher than other reported PANI cathodes. Experimental results suggest that the charge storage mechanism of PANI-V10 O28 includes reversible injection/extraction of Zn(H2 O)2 Cl4 2- ions in PANI, as well as the protonation/deprotonation of V10 O28 6- . This work enriches the doping chemistry of conducting polymer and pushes the development of organic cathodes for ARZBs to a new stage.

Solid-Liquid Interfacial Coordination Chemistry Enables High-Capacity Ammonium Storage in Amorphous Manganese Phosphate.

Ammonium (NH4 + ) ion as charge carrier is attracting attention in aqueous batteries. Yet, most NH4 + host materials are still limited by the relatively low capacities. Here, we fabricated a manganese phosphate (MP-20) for NH4 + ion storage. MP-20 displays a high capacity of 299.6 mAh g-1 at 1 A g-1 in ammonium acetate (NH4 Ac) electrolyte, outperforming other reported NH4 + host materials. Spectroscopy studies suggest a new NH4 + /H+ co-insertion mechanism. We surprisingly discover that the NH4 Ac electrolyte plays an important role in improving the charge storage capability of the materials. Experimental and computational results indicate acetate ions can form coordination bonds with the Mn atoms, tailoring the electronic structure of the Mn atoms and the surrounding O atoms, and therefore facilitating the NH4 + storage process. Our findings provide a new NH4 + host material and propose the important role of the electrolyte-electrode coordination effect in aqueous ammonium batteries.

Ammonium-Ion Storage Using Electrodeposited Manganese Oxides.

NH4 + ions as charge carriers show potential for aqueous rechargeable batteries. Studied here for the first time is the NH4 + -storage chemistry using electrodeposited manganese oxide (MnOx ). MnOx experiences morphology and phase transformations during charge/discharge in dilute ammonium acetate (NH4 Ac) electrolyte. The NH4 Ac concentration plays an important role in NH4 + storage for MnOx . The transformed MnOx with a layered structure delivers a high specific capacity (176 mAh g-1 ) at a current density of 0.5 A g-1 , and exhibits good cycling stability over 10 000 cycles in 0.5 M NH4 Ac, outperforming the state-of-the-art NH4 + hosting materials. Experimental results suggest a solid-solution behavior associated with NH4 + migration in layered MnOx . Spectroscopy studies and theoretical calculations show that the reversible NH4 + insertion/deinsertion is accompanied by hydrogen-bond formation/breaking between NH4 + and the MnOx layers. These findings provide a new prototype (i.e., layered MnOx ) for NH4 + -based energy storage and contributes to the fundamental understanding of the NH4 + -storage mechanism for metal oxides.

Inhibiting VOPO4 ⋠x H2 O Decomposition and Dissolution in Rechargeable Aqueous Zinc Batteries to Promote Voltage and Capacity Stabilities.

VOPO4 ⋅x H2 O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf)2 electrolyte. Investigations show the decomposition of VOPO4 ⋅x H2 O into VOx in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO4 3- was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl2 salt in the electrolyte further prevents VOPO4 ⋅x H2 O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl2 /0.8 m H3 PO4 aqueous electrolyte, in direct contrast to that in Zn(OTf)2 where the decomposition product VOx provides most electrochemical activity over cycling. Sequential H+ and Zn2+ intercalations into the structure are revealed, delivering a high capacity (170 mAh g-1 ). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles.

1 T-MoSe2 monolayer supported single Pd atom as a highly-efficient bifunctional catalyst for ORR/OER.

The development of highly-efficient catalysts for oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) is highly crucial for the commercial applications of some novel energy-related devices. Herein, using comprehensive first-principles computations, the potential of a variety of single metal-based catalysts supported by MoSe2 nanosheet to boost the ORR or OER process was evaluated. The computations revealed that these considered metal atoms can be more stably anchored on 1 T-MoSe2 than those of on 2H-MoSe2. In particular, the supported Ni and Pd catalysts on 1 T-MoSe2 exhibit high OER activity due to their quite low overpotential (0.47 and 0.49 V). Meanwhile, the anchored Pd atom on 1 T-MoSe2 also displays excellent ORR performance with an ultra-low overpotential of 0.32 V, thus implying its superior bifunctional activity for ORR/OER. Our results provide a quite promising avenue to design a new class of MoSe2-based single atom catalysts for fuel cells, which also further enriches the application fields of MoSe2 nanosheets in advanced catalysis.

Computational screening of single-atom catalysts supported by VS2 monolayers for electrocatalytic oxygen reduction/evolution reactions.

The development of highly efficient bifunctional electrocatalysts to boost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable for energy conversion and storage devices. Herein, by means of comprehensive first-principles computations, we systematically explored the catalytic activities of a series of single transition metal atoms anchored on two-dimensional VS2 monolayers (TM@VS2) for ORR/OER. Our results revealed that Ni@VS2 exhibits low overpotentials for both ORR (0.45 V) and OER (0.31 V), suggesting its great potential as a bifunctional catalyst, which is mainly induced by its moderate interaction with oxygenated intermediates according to the established scaling relationship and volcano plot. Interestingly, the substituted doping of nitrogen heteroatoms into the VS2 substrate can further effectively improve the ORR/OER activity of the active metal atom to achieve more eligible ORR/OER bifunctional catalysts. Our results not only propose a new class of potential bifunctional oxygen catalysts but also offer a feasible strategy for further tuning their catalytic activity.

Protonating imine sites of polyaniline for aqueous zinc batteries.

PANI materials usually contain a certain amount of insulating components, e.g., imine (N-) and amine (-NH-) groups, limiting the electrochemical redox of PANI. Herein, we proposed a simple protonation strategy to activate the redox couples of the PANI cathode for aqueous Zn batteries, during which the insulating N- groups are partially converted to the conductive emeraldine salt (polarons -NH+-), endowing PANI more active sites and enhanced conductivity. The A-PANI electrode realizes efficient transitions of leucoemeraldine/emeraldine and emeraldine/pernigraniline, achieving a high discharge capacity of 183 mA h g-1, long life span, and good energy density of 178 W h kg-1 at the power density of 680 W kg-1. These values are significantly superior to those of the original PANI electrode, indicating the high efficiency of the proposed strategy. This simple protonation method could be applicable for many electrochemical devices, such as supercapacitors, sensors, and batteries.

N-Doped CrS2 Monolayer as a Highly-Efficient Catalyst for Oxygen Reduction Reaction: A Computational Study.

Searching for low-cost and highly-efficient oxygen reduction reaction (ORR) catalysts is crucial to the large-scale application of fuel cells. Herein, by means of density functional theory (DFT) computations, we proposed a new class of ORR catalysts by doping the CrS2 monolayer with non-metal atoms (X@CrS2, X = B, C, N, O, Si, P, Cl, As, Se, and Br). Our results revealed that most of the X@CrS2 candidates exhibit negative formation energy and large binding energy, thus ensuring their high stability and offering great promise for experimental synthesis. Moreover, based on the computed free energy profiles, we predicted that N@CrS2 exhibits the best ORR catalytic activity among all considered candidates due to its lowest overpotential (0.41 V), which is even lower than that of the state-of-the-art Pt catalyst (0.45 V). Remarkably, the excellent catalytic performance of N@CrS2 for ORR can be ascribed to its optimal binding strength with the oxygenated intermediates, according to the computed linear scaling relationships and volcano plot, which can be well verified by the analysis of the p-band center as well as the charge transfer between oxygenated species and catalysts. Therefore, by carefully modulating the incorporated non-metal dopants, the CrS2 monolayer can be utilized as a promising ORR catalyst, which may offer a new strategy to further develop eligible electrocatalysts in fuel cells.

Enabling Reversible MnO2/Mn2+ Transformation by Al3+ Addition for Aqueous Zn-MnO2 Hybrid Batteries.

Aqueous rechargeable Zn-manganese dioxide (Zn-MnO2) hybrid batteries based on dissolution-deposition mechanisms exhibit ultrahigh capacities and energy densities due to the two-electron transformation between MnO2/Mn2+. However, the reported Zn-MnO2 hybrid batteries usually use strongly acidic and/or alkaline electrolytes, which may lead to environmental hazards and corrosion issues of the Zn anodes. Herein, we propose a new Zn-MnO2 hybrid battery by adding Al3+ into the sulfate-based electrolyte. The hybrid battery undergoes reversible MnO2/Mn2+ transformation and exhibits good electrochemical performances, such as a high discharge capacity of 564.7 mAh g-1 with a discharge plateau of 1.65 V, an energy density of 520.8 Wh kg-1, and good cycle life without capacity decay upon 2000 cycles. Experimental results and theoretical calculation suggest that the aquo Al3+ with Brønsted weak acid nature can act as the proton-donor reservoir to maintain the electrolyte acidity near the electrode surface and prevent the formation of Zn4(OH)6(SO4)·0.5H2O during discharging. In addition, Al3+ doping during charging introduces oxygen vacancies in the oxide structure and weakens the Mn-O bond, which facilitates the dissolution reaction during discharge. The mechanistic investigation discloses the important role of Al3+ in the electrolyte, providing a new fundamental understanding of the promising aqueous Zn-MnO2 batteries.

The energy storage behavior of a phosphate-based cathode material in rechargeable zinc batteries.

The energy storage behavior of the Li3V2(PO4)3 cathode in zinc batteries is evaluated. The dissolution or decomposition into vanadium oxide in aqueous electrolytes is revealed. Using the optimal combination of water and acetonitrile solvents in electrolyte, those processes are effectively prevented without sacrificing the Zn2+ de/insertion kinetics. Further investigation demonstrates a water induced phase transformation into a VOPO4 type structure, which is still a polyanion material and preserves the high voltage. It delivers 128 mA h g-1 capacity at 1C with 1.45 V discharge voltage, and 87 mA h g-1 capacity is retained at 10C. A stable cycling is obtained for 1000 cycles.