Bare ZnO Research Articles

Construction of Zinc‐based Anodes for Electrolytic Zinc‐MnO2 Batteries with High Discharge Voltage and Good Durability

AbstractRechargeable aqueous zinc‐MnO2 batteries have attracted great attention owing to their advantages on safety, power density, and cost. In strong acidic environment, the capacity of MnO2‐based cathode can reach 616 mAh g−1 through a two‐electrons‐transfer process of Mn2+↔MnO2. However, in acidic environment, Zn corrosion, dendrites, and hydrogen evolution reaction (HER) on the anode are rather serious, resulting in low Columbic efficiency (CE) and poor durability. Towards these issues, ZnO with dual‐protection, including C and polyvinyl alcohol (PVA) coating (ZnO@C‐PVA), is developed as initial anode material herein. Compared with bare CC, ZnO, and ZnO@C, reversibility of the ZnO@C‐PVA electrode is largely enhanced. CE of an electrolytic full system using ZnO@C‐PVA as anode and bare carbon cloth (CC) as cathode can be as high as 90 % at 5 mA cm−2, and discharge voltage is up to 1.85 V (mid‐value), which can be maintained for 1,600 cycles, indicating rather good stability. It is believed that the existence of initial ZnO can tune the local pH around the anode, resulting in the decrease of HER and the enhancement of Zn plating. Besides, corrosion and Zn dendrites also can be inhibited effectively by the PVA layer.

Enhancing the photoelectrochemical performance of ZnO nanopagoda photoanode through sensitization with Ag and Ag2S NPs co-deposition

ZnO nanopagoda arrays (NPGs) modified with Ag and Ag2S nanoparticles (NPs) were fabricated using aqueous downward growth and SILAR techniques and investigated as photoanodes for the photoelectrochemical system. The crystal structure, morphology, elemental composition, optical characteristics, and photoelectrochemical performance of the fabricated samples were studied. The obtained results disclosed that the successful deposition of Ag and Ag2S NPs on ZnO NPGs’ surface not only enhanced the visible light-harvesting but also promoted the e−/h+ separation and injection. In addition, various SILAR cycles were investigated. The optimum eight SILAR cycles for Ag–Ag2S NPs deposition on ZnO NPGs achieved the maximum photocurrent of 2.91 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), about five folds superior to that of bare ZnO NPGs. It also demonstrated the improved applied bias photon-to-current conversion efficiency of 0.43% at 0.6 V vs. RHE. The charge transfer and PEC mechanisms for the fabricated ZnO NPGs/Ag–Ag2S NPs photoanodes were also proposed. This study offers a facile fabrication of a distinctive ZnO NPGs morphology and an improvement of the PEC performance through the synergistic effect of the LSPR effect of Ag NPs and visible light sensitization of Ag2S NPs.

Review of Recent Developments in the Fabrication of ZnO/CdS Heterostructure Photocatalysts for Degradation of Organic Pollutants and Hydrogen Production.

Researchers have recently paid a lot of attention to semiconductor photocatalysts, especially ZnO-based heterostructures. Due to its availability, robustness, and biocompatibility, ZnO is a widely researched material in the fields of photocatalysis and energy storage. It is also environmentally beneficial. However, the wide bandgap energy and quick recombination of the photoinduced electron-hole pairs of ZnO limit its practical utility. To address these issues, many techniques have been used, such as the doping of metal ions and the creation of binary or ternary composites. Recent studies showed that ZnO/CdS heterostructures outperformed bare ZnO and CdS nanostructures in terms of photocatalytic performance when exposed to visible light. This review largely concentrated on the ZnO/CdS heterostructure production process and its possible applications including the degradation of organic pollutants and hydrogen evaluation. The importance of synthesis techniques such as bandgap engineering and controlled morphology was highlighted. In addition, the prospective uses of ZnO/CdS heterostructures in the realm of photocatalysis and the conceivable photodegradation mechanism were examined. Lastly, ZnO/CdS heterostructures' challenges and prospects for the future have been discussed.

Developed interfacial charge transport in super-dimensional CuO branched ZnO nanorods array (CuO B ZnO NRsA)

Hierarchical CuO nanobranches have been synthesized through reactive etching of Cu thin film (50–200 nm in thickness) on hydrothermally processed ZnO nanorods array (ZnO NRsA), which in turn fabricated multi-interfacial CuO- ZnO heterostructure. The structural, morphological, elemental content and optical properties of CuO branched ZnO NRs array (CuO – B ZnO NRsA) heterostructures have been investigated by X-ray diffractometry (XRD), field emission- scanning electron microscope/ energy dispersive X-ray spectroscopy (FE-SEM /EDX) and UV–Vis- near IR optical absorption spectroscopy, respectively.Chemical etching modifies the surface morphology and manipulates one-dimensional hyperstructures. The CuO – B ZnO NRsA heterostructures improve/expand the optical absorption to visible region in comparison to the bare ZnO NRsA. The charge transferring in CuO – B ZnO NRsA hetero-interface has been engineered, by controlling the thickness of Cu thin film which tuned the electrical conductance and photocatalytic performance. The interfacial electric field can rapidly separate and drift the photoinduced charge carriers, which induces the highest photodegradation efficiency for the reduction of RhB. The electronic transport and the photocatalytic performance can be tuned by length of CuO branches.

A Novel ZnO/Co3O4 Nanoparticle for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

In recent years, ZnO/Co3O4 nanoparticles (NPs) have been reflected as typical of the most promising photocatalysts utilized in the field of photocatalysis for potentially solving energy shortages and environmental remediation. In this work, a novel ZnO/Co3O4 NP photocatalyst was fabricated and utilized for photocatalytic hydrogen evolution with visible light activity. ZnO/Co3O4 NPs display an improved photocatalytic hydrogen production rate of 3963 μmol/g through a five-hour test under visible light activity. This is much better than their single components. Hence, bare ZnO NPs loaded with 20 wt% Co3O4 NPs present optimum efficiency of hydrogen evolution (793.2 μmol/g/h) with 10 vol% triethanolamine (TEOA), which is 11.8 times that of pristine ZnO NPs. An achievable mechanism for improved photocatalysis is endowed in terms of the composite that promotes the operative separation rate of charge carriers that are produced by visible light irradiation. This study yields a potential process for the future, proposing economical, high-function nanocomposites for hydrogen evolution with visible light activity.

Microwave-assisted hydrothermal synthesis of type II ZnSe/ZnO heterostructures as photocatalysts for wastewater treatment

The ZnSe/ZnO heterostructures were synthesized with the microwave-assisted hydrothermal method, using zinc acetate and zinc nitrate as a source of Zn2+ ions. Materials were characterized by X-ray diffraction (XRD), X-ray photoemitted electron spectroscopy (XPS), Raman spectroscopy, and scanning electron microscopy (SEM). The incorporation of ZnSe into the ZnO matrix produced changes both in the size of the ZnO crystallites and in the lattice parameters. Optical and texture analyses revealed that ZnSe particles cause a decrease in gap energy and a greater than 90% increase in the specific surface area of ZnSe/ZnO heterostructures compared to bare ZnO particles. ZnSe/ZnO heterostructures synthesized using zinc acetate as a Zn ion source exhibited better photocatalytic performance in visible light compared to pure ZnO.

A synergistic effect between ZnO/CdS S-scheme heterojunction and GO cocatalyst for boosting photocatalytic performance

ZnO nanosheets, 2D/1D ZnO/CdS hybrid and ternary ZnO/CdS/GO S-scheme heterojunction photocatalyst were fabricated by a low-temperature hydrothermal technique. As expected, by investigating the degradation efficiency of rhodamine B under simulated sunlight, with the assistance of CdS and GO, the ternary heterostructure showed superior photocatalytic activity. The test results display that the dye degradation rate constant of ZnO/CdS/GO is about 1.75 × 10−2 min−1, which is 3.6 times higher than that of bare ZnO. SEM results prove the finding that the content of CdS can regulate the size and distribution of ZnO NSs, increasing the specific surface area of the sample. Besides, the results of ultraviolet–visible (UV–vis) absorbance spectra revealed that the addition of CdS and GO significantly synergistically increased the visible light absorption of ZnO, and also shortened the band gap of ZnO. Photoluminescence (PL) spectra, electrochemical impedance spectroscopy (EIS) and transient photocurrent response (TPR) results show that the presence of CdS and GO synergistically promotes the rapid separation of photoexcited carriers in ZnO. Notably, the GO also further speeds up the transmission rate of electrons and improves the photoelectric stability of the ZnO/CdS heterogeneous photocatalyst. The above changes can effectively promote the photocatalytic performance of photocatalysts. Moreover, a reasonable S-scheme carriers migration mechanism was proposed with the assistance of Mott-Schottky (MS) test, VB-XPS and sacrificial agent experiments. Through comprehensive analysis and discussion, it can be concluded that ZnO/CdS S-scheme heterojunction and GO synergistically promote the photocatalytic performance of ZnO. Therefore, this thesis may provide a deeper insight into developing the practical application of ZnO-based heterojunction photocatalysts in pollutant degradation.

Conductometric sensor for gaseous sulfur-mustard simulant by gold nanoparticles anchored on ZnO nanosheets prepared via microwave irradiation

We report the microwave-assisted synthesis of Au nanoparticles (NPs) anchored porous ZnO nanosheets (Au-ZnO NSs) and their application in the sensitive detection of 2-chloroethyl ethyl sulfide (2-CEES) vapors, which are a simulant of sulfur mustard chemical weapon. Upon microwave irradiation for < 1 min with an annealing, highly crystalline Au NPs with a narrow particle-size distribution (2.32 ± 0.40 nm) are densely formed on the surface of porous ZnO NSs, which increases the density of oxygen vacancies in the ZnO. Under the optimal working temperature (450 °C), the response of the Au-ZnO NS sensor was measured to be 787 for 10 ppm 2-CEES, which is ∼14 times higher than that observed for the bare porous ZnO NSs-based sensor. Moreover, Au-ZnO NSs can detect 2-CEES gas even under high humidity (∼80 %) benefiting from its high sensitivity. The highly reproducible sensing performance was verified by repeated sensing test (20 times for 12 h). According to gas screening data, the Au-ZnO NSs exhibited outstanding selectivity toward sulfide compounds due to the high Au-S affinity. In summary, we have successfully demonstrated a simple and facile approach to form the Au-ZnO heterostructure by microwave irradiation and enhanced the gas-sensing performance by inducing catalytic activity.

PbS quantum dots-sensitized ZnO nanorods-based third generation solar cells

PbS quantum dots (QDs) and PbS QDs-sensitized ZnO nanostructures of rod-like shape have been synthesized by the successive ionic layer adsorption and reaction method. The optical absorption spectra PbS QDs indicate that the prepared sample exhibits significant visible light absorption. The light absorption of PbS QDs-sensitized ZnO nanorods (NRs) was higher than bare ZnO NRs. X-ray diffraction pattern of PbS QDs exhibits diffraction peaks corresponding to (200), (112), and (202) planes of PbS. A Uniform development of ZnO nanostructures of rod-like shape and the PbS QDs deposition over its surface was witnessed from the field-emission scanning electron microscope and transmission electron microscope images. The small ring pattern confirming the polycrystalline nature of the prepared PbS thin film was observed from the selected area electron diffraction pattern. Solar cells were made using PbS QDs-sensitized ZnO NRs as photoanodes and it exhibited a power conversion efficiency of 1.2%.

Facile synthesis of ZnO/ZnS hollow nanorods via Kirkendall effect with enhanced photocatalytic degradation of methylene blue.

Because of the growing concerns about environmental issues, the search of proficient semiconductor catalysts for pollutants degradation from contaminated water is one of the interesting areas of research. Due to the larger surface area, hollow nanomaterials with hollow interior and outer thickness illustrate a class of significant nanostructured materials. The enhanced surface area provides remarkable applications of the hollow nanomaterials in catalysis. In Kirkendall effect, pores are formed owing to the diverse diffusion rates of two nanomaterials in a diffusion couple. Here, we have introduced the facile hydrothermal synthesis of hollow nanorods of ZnO/ZnS via Kirkendall effect using ZnO nanorods (NRs). The morphologies, optical properties, compositions, and crystal structures of the as synthesized materials are systematically studied using UV-vis, PXRD, FESEM, TEM, EDS, XPS, etc. The process of synthesis and growth mechanism of hollow NRs is suggested based on the Kirkendall effect. A hollow nanomaterial, envisaged being highly efficient for molecule adsorption on its surface, the as synthesized materials were used for the photocatalytic degradation of methylene blue (MB) dye. MB degradation efficiency of 96% within 60min was performed over ZnO/ZnS hollow NRs, which was 2.6-fold greater than that of ZnO. The rate constant of ZnO/ZnS heterostructure was 0.045min-1, which was 5.5 times larger than that of bare ZnO. We have concluded our work in the directions towards the synthesis of various semiconductor hollow nanostructures for the varied catalytic reactions.

Conversion of both photon and mechanical energy into chemical energy using higher concentration of Al doped ZnO

Synthesis of materials to harvest photon energy together with mechanical energy beneficial to address the current energy shortage and enhance the photocatalytic properties of the material. Bare ZnO displays poor photocatalytic properties under visible light illumination owing to higher bandgap energy. Intrinsic defect engineering of ZnO lattice by Al doping enhance the visible light harvesting ability and the better piezoelectric properties contribute additional electron in the lattice would upsurge the piezo-photocatalytic property under the visible region. Aluminum doped in ZnO lattice prepared by two-step sintering method in which the Al doped ZnO (AZO) sintered at 150 °C for one hour and followed by 500 °C for two hours. The enhanced piezo-photocatalytic properties verified based on the piezo-photocatalytic degradation of Methylene blue dye under visible light together with mechanical vibration. The enhanced piezo-photocatalytic activity attributed to enhanced visible light harvesting via defects in the lattice, freely existence of electron in the AZO lattice, enhanced surface area and zinc/oxygen vacancies in the lattice. The AZO shows better piezo-photocatalytic properties and almost 53.7% enhanced piezo-photocatalytic efficiency than the bare ZnO under the visible light illumination. This work highlights the attractive piezo-photocatalytic properties of 10% Al-doped ZnO (AZO-10) via strong coupling of visible light harvesting and piezoelectricity to convert both photon and mechanical energy into chemical energy.

Tailoring the surface chemistry of ZnO nanowires via mixed self-assembly of organosilanes for selective acetone detection

We are proposing a novel active sensing surface based on mixed-SAMs (APTES and TEOS) functionalized ZnO nanowires (NWs) for selective detection of acetone. We showed that mixed-SAMs are a superior strategy for sensing performance enhancement not only from bare ZnO NWs but also from homogenous SAM provided suitable mixing ratios were selected. The mixed-SAMs functionalized NWs exhibit high selectivity toward acetone with a response value of 256 ± 36 (50 ppm) due to the molecular interaction between the acetone C═O group and terminal—CH3 and —NH2 groups of SAMs. Indeed, for the very first time, the effect of the mixing ratio on the sensing performance was systematically discussed in this work which is one of the most important aspects of the mixed-SAM approach. In particular, two main factors i.e., the variation in the charge distribution of mixed-monolayer and the modification in the molecular interactions between terminal SAMs groups acetone carbonyl group caused by mixing ratio plays the key role. Functionalized sensors exhibit high stability for the period of 2-months with lowest detection limit of 0.05 ppm, makes them a potential candidate for acetone exhaled breath analysis.

Au-doped ZnO@ZIF-7 core-shell nanorod arrays for highly sensitive and selective NO2 detection

The exploration of novel NO2 sensors with high performance is of great importance for air quality monitoring and human health. In this work, Au-doped ZnO@ZIF-7 core-shell nanorod arrays were fabricated for high-performance NO2 detection. Due to the spill-over effects of Au nanoparticles, gas enriching and molecular sieving effects provided by ZIF-7 membranes, the ZnO-Au@ZIF-7 sensor affords highly sensitive and selective detection of NO2. The heterostructured ZnO-Au@ZIF-7 allows for ppb-level detection of NO2 (Response = 1.7–5 ppb) with excellent repeatability and provides improved selectivity, anti-humidity capacity, and long-term stability compared with bare ZnO, Au-doped ZnO or ZnO@ZIF-7 core-shell nanorod arrays. According to the calculation of density functional theory (DFT), the ZnO-Au@ZIF-7 sensor renders higher adsorption energy towards NO2 molecules compared with the aforementioned other materials, which also explains its outstanding sensing performances. We believe our approach that combines noble metals doped semiconductor metal oxides (SMOs) and MOF filtration membranes can be further extended to numerous new heterostructured SMO@MOF materials, which opens venues to the development of advanced chemiresistive gas sensors.

Synthesis and characterization of phytochemical fabricated Ag doped ZnO nanoparticles with Ficus benghalensis and their enhanced antibacterial and photocatalytic applications

The use of various plant materials for the bio synthesis of metal oxide nanoparticles follows the principles of green chemistry since it minimizes the amount of chemicals used. In the present work, ZnO and Ag doped ZnO nanoparticles were synthesized utilizing aqueous leaf extract of Ficus benghalensis. The aqueous leaf extract was screened qualitatively for the presence of chemical constituents. The nanoparticles ZnO, green modified ZnO and Ag doped ZnO were characterized by X-ray diffraction (XRD), FT-IR, EDAX and Scanning Electron Microscope (SEM). The optical properties were studied using UV-Vis-DRS spectroscopy and a bathochromic shift is observed in the band gap energy of synthesized Ag doped ZnO. From XRD, the particle size of the ZnO, green modified ZnO and Ag doped ZnO nanoparticles was found to be 36, 39 and 53 nm respectively. Photodegradation of crystal violet dye was studied by UV-Visible spectroscopy. The degradation ability of the surface modified ZnO was found to be more efficient than that of bare ZnO and green modified ZnO nanoparticles. The photocatalytic reactions obeyed pseudo-first-order kinetics according to Langmuir- Hinshelwood model. The reuse of nanoparticles for photocatalytic activity was also studied.

Highly sensitive and self powered ultraviolet photo detector based on ZnO nanorods coated with TiO2

Nanorods (NRs) of crystalline ZnO coated with thin layers of TiO$_2$(ZnO@TiO$_2$) were fabricated with the help of the spin coating technique followed by the hydrothermal method. Scanning electron microscopy (SEM) and X-ray diffraction analysis confirms the morphology and structural stability of as-prepared NRs. The optical band gaps of the NRs were estimated, and a clear blue shift toward the UV region has been detected. When UV light falls on as-prepared device (i.e., in the "ON" state), a significant increase in photocurrent (I$_{UV}$) at zero voltage supply was observed from 6 $\mu$A to 17 $\mu$A while in the "OFF" state, the dark current (I$_{dark}$), increases from 0.08 $\mu$A to 0.6 $\mu$A with ZnO@TiO$_2$ NRs as compared to bare ZnO NRs respectively. Responsivity and detectivity of TiO$_2$ coated ZnO NRs based device found maximum in UV region unlike bare ZnO NRs. Enhanced photocurrent achieved by the growth of TiO$_2$ layers on ZnO NRs is 250 $\mu$A as compared to bare ZnO NRs for which it is 35 $\mu$A at 10 V voltage supply under the ultraviolet irradiation (illumination intensity of 1 mW/cm$^2$). Furthermore, theoretical calculations have been performed using the first-principles density-functional theory to understand the effects of heterostructure NRs on the electronic and optical properties of TiO$_2$ coated ZnO.

Efficient photodegradation of methyl orange and bactericidal activity of Ag doped ZnO nanoparticles

In the present work, silver-doped ZnO (Ag–ZnO NPs) with different concentrations of silver ions (0.3, 0.5, 1.0 and 1.5 mol %) were synthesized by using a simple co-precipitation method. The Ag–ZnO NPs were primarily characterized by XRD, FT-IR, SEM, EDS, TEM, UV–Vis. DRS, PL and BET surface area. The XRD analysis of Ag–ZnO NPs shows a wurtzite structure and optimized Ag–ZnO NPs (1.0 mol %) exhibit a lower crystallite size of 15.96 nm than that of bare ZnO (19.07 nm). Optical study shows a decrease in band gap from 3.13 to 2.97 eV as the concentration of Ag ions increases from 0.3 to 1.5 mol%. TEM images reveal the spherical shape particle with sizes ranging between 10 and 15 nm. From the multipoint BET plot, the surface area of Ag–ZnO NPs found 38.06 m2/gwhich is higher than the ZnO NPs (34.48 m2/g). The photocatalytic study demonstrated that the Ag–ZnO NPs (1.0 mol %) has an excellent photodegradation efficiency of Methyl Orange (96.74%)with a 26% increment as compared to bare ZnO (70.47%). Furthermore, the bactericidal activity of Ag–ZnO NPs (1.0 mol %) was investigated against four different bacterial strains. The results explored that the Gram-negative bacteria (E. coli and P. vulgaris) are more sensitive than Gram-positive (S. aureus and B. cereus) to Ag–ZnO NPs. Overall, the anticipated material is economical and reusable for photodegradation and antibacterial activity.

Construction of a novel ZnO/rGO hybrid composite for efficient degradation of CV, Cr (VI) and 2, 4-D under visible light irradiation

The pristine ZnO and ZnO-Graphene hybrid composites at various graphene ratios were synthesized via facile ultrasonic assisted solution approach. The crystal structure is identified by powder XRD technique and disclosed the hexagonal wurtzite structure. The synthesized ZnO exhibited uniform spherical like morphology with low degree of aggregation. The formation of hybrid composite of graphene and ZnO could improve the light absorption ability and separation of photo generated carriers of ZnO, which is confirmed through photoluminescence and UV–Vis DRS analysis. The photo catalytic degradation of Crystal violet, Cr (VI) and 2, 4 D were evaluated under visible light irradiation. The Zn-Graphene hybrid composite exhibited higher photo catalytic activity towards CV dye, Cr (VI) and 2, 4-D, such as high photo degradation efficiency and good stability than bare ZnO. This could be due to the high surface area and synergic effect between the graphene and ZnO p–n junctions. The mechanism of enhanced photo catalytic activity of Zn-Graphene composite discussed in detail.

S,N-GQD sensitization effect on the improvement of ZnO nanopencil photoelectrochemical properties.

ZnO photoanodes in photoelectrochemical (PEC) water splitting for green-hydrogen production are limited due to the large bandgap that is only confined to UV light. One of the strategies for broadening the photo absorption range and improving light harvesting is to modify a one-dimensional (1D) nanostructure to a three-dimensional (3D) ZnO superstructure coupling with a narrow-bandgap material, in this case, a graphene quantum dot photosensitizer. Herein, we studied the effect of sulfur and nitrogen co-doped graphene quantum dot (S,N-GQD) sensitization on the surface of ZnO nanopencil (ZnO NPc) to give a photoanode in the visible light spectrum. In addition, the photo energy harvesting between the 3D-ZnO and 1D-ZnO, as represented by neat ZnO NPc and ZnO nanorods (ZnO NRs), was also compared. Several instruments, including SEM-EDS, FTIR, and XRD revealed the successful loading of S,N-GQDs on the ZnO NPc surfaces through the layer-by-layer assembly technique. The advantages are S,N-GQDs's band gap energy (2.92 eV) decreasing ZnO NPc's band gap value from 3.169 eV to 3.155 eV after being composited with S,N-GQDs and facilitating the generation of electron-hole pairs for PEC activity under visible light irradiation. Furthermore, the electronic properties of ZnO NPc/S,N-GQDs were improved significantly over those of bare ZnO NPc and ZnO NR. The PEC measurements revealed that the ZnO NPc/S,N-GQDs stood out with a maximum current density of 1.82 mA cm-2 at +1.2 V (vs. Ag/AgCl), representing a 153% and 357% improvement over the bare ZnO NPc (1.19 mA cm-2) and the ZnO NR (0.51 mA cm-2), respectively. These results suggest that ZnO NPc/S,N-GQDs could have potential for water splitting applications.

Control of the resistive switching voltage and reduction of the high-resistive-state current of zinc oxide by self-assembled monolayers.

We investigated the effect of self-assembled monolayer (SAM) modification of ZnO on the resistive switching behaviour by fabricating electrode-sandwiched devices (ITO/ZnO-SAM/Al). The resistive switching voltages of SAM-modified ZnO films were shifted from that of bare ZnO depending on the surface dipole induced by the SAMs. In particular, methylaminopropyl-substituted SAM-modified ZnO showed lower switching voltage (1.6 V) than bare ZnO (2.9 V). Moreover, the on/off ratio was also improved by SAM modification (from 102 to 104).

Rational design of ZnO-based aqueous batteries for safe, fast, and reliable energy storage: Accomplishment of stable K+ storage/release

Rechargeable aqueous batteries are attractive for grid-scale applications. Yet, their broad adoption is hindered by the unsatisfactory durability, capacity, and Coulombic efficiency (CE). To alleviate these problems, we report a new Ni-Zn system composed of our newly developed concentrated CH3COOK (KAc) gel electrolyte, a ZnO@C anode, and a commercial Ni(OH)2 cathode. In this system, the ZnO@C anode demonstrates significantly improved stability than bare ZnO electrode (or ZnO@C in liquid KOH), and displays a reversible capacity of 400 mAh/g after 50 cycles at 1 A/g. Most importantly, the full cell demonstrates an ultrahigh midpoint discharge voltage of about 2.1 V, which is ∼0.5 V higher than that of traditional Ni-Zn battery with KOH as electrolyte. With Zn(OH)42- source in the gel, capacity and durability of the anode are largely enhanced, achieving 540 mAh/g for ∼450 cycles at 1 A/g. Surprisingly, the reversibility is increased with the increase of discharge current, achieving a capacity of 640 mAh/g at 4–8 A/g while maintaining CE as high as 97.3 % for the whole cell. After carefully analysis, it is found that stable and reversible K+ insertion but not Zn/Zn(OH)42- dominates the reaction mechanism and takes main contribution to the high voltage; While, the concentrated gel electrolyte, the C coating layer, and the solid electrolyte interphase (SEI) formed during cycling play the major role on durability and CE.