Higher Peak Discharge Research Articles

A simple approach to estimate daily loads of total, refractory, and labile organic carbon from their seasonal loads in a watershed.

Loads of naturally occurring total organic carbons (TOC), refractory organic carbon (ROC), and labile organic carbon (LOC) in streams control the availability of nutrients and the solubility and toxicity of contaminants and affect biological activities through absorption of light and complex metals with production of carcinogenic compounds. Although computer models have become increasingly popular in understanding and management of TOC, ROC, and LOC loads in streams, the usefulness of these models hinges on the availability of daily data for model calibration and validation. Unfortunately, these daily data are usually insufficient and/or unavailable for most watersheds due to a variety of reasons, such as budget and time constraints. A simple approach was developed here to calculate daily loads of TOC, ROC, and LOC in streams based on their seasonal loads. We concluded that the predictions from our approach adequately match field measurements based on statistical comparisons between model calculations and field measurements. Our approach demonstrates that an increase in stream discharge results in increased stream TOC, ROC, and LOC concentrations and loads, although high peak discharge did not necessarily result in high peaks of TOC, ROC, and LOC concentrations and loads. The approach developed herein is a useful tool to convert seasonal loads of TOC, ROC, and LOC into daily loads in the absence of measured daily load data.

Highly Stabilized Zinc‐Air Batteries Based on Nanostructured Co3O4 Composites as Efficient Bifunctional Electrocatalyst

AbstractZinc‐air batteries are expected to be ideal energy storage devices, showing features of high energy density, economic viability, and safety. To design such a system, it is necessary to develop active and durable electrocatalysts to catalyze the slow oxygen reduction reaction (ORR) during discharging and the oxygen evolution reaction (OER) during charging. In this study, a composite bifunctional catalyst (Co3O4@CNT@MC‐200) for use in zinc‐air batteries is prepared through a simple sol‐gel method, which combines Co3O4 with carbon nanotubes (CNTs) and mesoporous carbon (MC). Benefiting from its large specific surface area and, thus, a multitude of active sites, the Co3O4@CNT@MC‐200 composite bifunctional electrocatalyst shows excellent ORR performance in 0.1 M KOH, resulting in a half‐wave potential (E1/2) of 0.72 V and limiting diffusion current of 4.6 mA cm−2. In zinc‐air battery tests, a high discharge peak power density of 267 mW cm−2 and robust lifetime of 8700 min without attenuation is observed. Moreover, the physical properties of the reported catalyst were characterized. This study allows us to envisage the design of highly efficient composite electrocatalysts for zinc‐air batteries and a variety of other energy applications.

The Diurnal and Semidiurnal Patterns of Rainfall and its Correlation to the Stream Flow Characteristic in the Ciliwung Watershed, West Java, Indonesia

Based on the data analysis of 16 years of TMPA dataset, the common patterns of rainfall over the Ciliwung River Basin are diurnal and semidiurnal. Those patterns can be associated by a stationary or moving rainstorm with different magnitude and direction. Based on hydrological model simulations, both the pattern and movement have a significant role to the discharge. At the downstream area, the discharge that triggered by semidiurnal pattern of rainfall can produces higher peak discharge and longer flood duration than diurnal pattern. This result open possibility to improve our prediction on design discharge.

Ice-Dammed Lake Drainage Evolution at Russell Glacier, West Greenland

Glaciological and hydraulic factors that control the timing and mechanisms of glacier lake outburst floods (GLOFs) remain poorly understood. This study used measurements of lake level at 15 min intervals and known lake bathymetry to calculate lake outflow during two GLOF events from the northern margin of Russell Glacier, west Greenland. We used measured ice surface elevation, interpolated subglacial topography and likely conduit geometry to inform a melt enlargement model of the outburst evolution. The model was tuned to best-fit the hydrograph rising limb and timing of peak discharge in both events; it achieved Mean Absolute Errors of <5%. About one third of the way through the rising limb, conduit melt enlargement became the dominant drainage mechanism. Lake water temperature, which strongly governed the enlargement rate, preconditioned the high peak discharge and short duration of these floods. We hypothesize that both GLOFs were triggered by ice dam flotation, and localized hydraulic jacking sustained most of their early-stage outflow, explaining the particularly rapid water egress in comparison to that recorded at other ice-marginal lakes. As ice overburden pressure relative to lake water hydraulic head diminished, flow became confined to a subglacial conduit. This study has emphasized the inter-play between ice dam thickness and lake level, drainage timing, lake water temperature and consequently rising stage lake outflow and flood evolution.

Evaluating the Applicability of Four Latest Satellite–Gauge Combined Precipitation Estimates for Extreme Precipitation and Streamflow Predictions over the Upper Yellow River Basins in China

This study aimed to statistically and hydrologically assess the performance of the four latest and widely used satellite–gauge combined precipitation estimates (SGPEs), namely CRT (CMORPH CRT), BLD (CMORPH BLD), CDR (PERSIANN CDR), 3B42 (TMPA 3B42 version 7) over the upper yellow river basins (UYRB) in china during 2001–2012 time period. The performances of the SGPEs were compared with the Chinese Meteorological Administration (CMA) datasets using the hydrologic model called Variable Infiltration Capacity (VIC) which is known as a land surface hydrologic model. Results indicated that irrespective of the slight underestimation in the western mountains and overestimation in the southeast, the four SGPEs could generally captured the spatial distribution of precipitation well. Although 3B42 exhibited a better performance in capturing the spatial distribution of daily average precipitation, BLD agreed best with CMA in the time series of watershed average precipitation, which resulted in BLD having a comparable performance to the CMA in the long-term hydrological simulations. Moreover, the potential for disastrous heavy rain mainly occurs in southeastern corner of the basin, and CRT and BLD comparisons showed to be closer to the CMA in the distribution of extreme precipitation events while 3B42 and CDR overestimated the extreme precipitation especially over the southeast of UYRB region. Therefore, CRT and BLD were able to match the high peak discharges very well for the wet seasons, while 3B42 and CDR overrated the high peak discharges. In addition, the four SGPEs performed well for the 2005 flood event but exhibited poorly when tested for the 2012 flood event. Results indicate that the application of the four SGPEs should be used with caution in simulating massive flood events over UYRB region.

Impact of forest maintenance on water shortages: Hydrologic modeling and effects of climate change

The importance of water quantity for domestic and industrial water supply, agriculture, and the economy more broadly has led to the development of many water quantity assessment methods. In this study, surface flow and soil water in the forested upper reaches of the Yoshino River are compared using a distributed hydrological model with Forest Maintenance Module under two scenarios; before and after forest maintenance. We also examine the impact of forest maintenance on these variables during extreme droughts. Results show that surface flow and soil water increased after forest maintenance. In addition, projections of future water resources were estimated using a hydrological model and the output from a 20km mesh Global Climate Model (GCM20). River discharge for the near-future (2015–2039) is similar to that of the present (1979–2003). Estimated river discharge for the future (2075–2099) was found to be substantially more extreme than in the current period, with 12m3/s higher peak discharge in August and 7m3/s lower in July compared to the discharges of the present period. Soil water for the future is estimated to be lower than for the present and near future in May. The methods discussed in this study can be applied in other regions and the results help elucidate the impact of forests and climate change on water resources.

Geo-hydrological analysis and sub watershed prioritization for flash flood risk using weighted sum model and Snyder’s synthetic unit hydrograph

The present study demonstrates the usefulness of remote sensing data for analyzing the flash flood risk in Uhl River watershed situated in the western Lesser Himalayan region. This is one of the most vulnerable flash flood watersheds in Himachal Pradesh which, suffers heavy damages to man-made features almost every year. In this study different morphometric properties that direct the hydrological response and pertinent to flash flood risk of the watershed have been used to prioritize the sub-watersheds using weighted sum analysis (WSA) model. The result indicates that 12.83 and 16.94 percent of the total area come under very high and high flash flood risk respectively. In addition, the Snyder’s synthetic unit hydrograph method was employed to assess the hydrological behavior and prioritization of sub-basins which shows that sub-basins falling under very high and high-risk group have low lag time and high peak discharge per unit of watershed area. This study concludes Watershed 7 and 8 of Uhl River basin in Himachal Pradesh comes under high priority class and is vulnerable to flash floods.

Reservoir’s Geometry Impact of Three Dimensions on Peak-Discharge of Dam Failure Flash Flood

Once a dam fails, large amount of water at rest in the reservoir releases to downstream river and can cause extensive inundation areas, damage to properties, and loss of lives. The outflow hydrograph influences from variety of factors; e.g. dam’s properties, failure mode, and reservoir specification. This paper aims to analyze the effect of two latter factors on the peak outflow discharge focusing on the relative size of the failed part employing failure ratio (a/A0) and shape of the reservoir employing shape factor (Sf) and cross section index (λ). Doing so, instantaneous experimental dam break and historical gradual failure were considered and separate analyses were carried out. Results showed that a higher peak-discharge is expected when Sf decreases or a/A0 and λ increase. Based on the experimental and historical dam failure data two distinct regression equations were developed and verified for peak-discharge estimation. The sensitivity analysis demonstrated that peak-discharge is highly sensitive to changes of the failure ratio and shape factor and it to some extend affects from cross section index.

Rational Design of High-Loading Sulfur Cathodes with a Poached-Egg-Shaped Architecture for Long-Cycle Lithium–Sulfur Batteries

A high-loading electrode is essential for establishing high-energy-density lithium–sulfur (Li–S) batteries, but it is confronted with critical challenges. Herein, we present a free-standing poached-egg-shaped architecture through a facile template-supported vacuum-filtration strategy and employ it as an efficient sulfur host for Li–S batteries. This unique architecture guarantees an effective encapsulation of the “sulfur yolk” inside the fully vacuum-sealed framework, effectively limiting the active material loss and polysulfide diffusion. Also, the conductive and porous framework serves as an interlinked electron pathway and electrolyte channel, greatly facilitating fast electric/ionic transport along with active material reactivation and reutilization during cycling. A high peak discharge capacity (1200 mA h g–1), a low capacity-fade rate (0.09% cycle–1) for 500 cycles, and excellent rate capability (C/5–1C rates) are accomplished. Moreover, with such an advantageous architecture, the sulfur loading is ...

A novel composite (FMC) to serve as a durable 3D-clam-shaped bifunctional cathode catalyst for both primary and rechargeable zinc-air batteries

Novel and highly durable air cathode electrocatalyst with three dimensional (3D)-clam-shaped structure, MnO2 nanotubes-supported Fe2O3 (Fe2O3/MnO2) composited by carbon nanotubes (CNTs) ((Fe2O3/MnO2)3/4-(CNTs)1/4) is synthesized using a facile hydrothermal process and a following direct heat-treatment in the air. The morphology and composition of this catalyst are analyzed using scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The morphology characteristics reveal that flower-like Fe2O3 particles are highly dispersed on both MnO2 nanotubes and CNT surfaces, coupling all three components firmly. Electrochemical measurements indicate that the synergy of catalyst exhibit superior bi-functional catalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as stability than Pt/C and IrO2 catalysts. Using these catalysts for air-cathodes, both primary and rechargeable zinc-air batteries (ZABs) are assembled for performance validation. In a primary ZAB, this 3D-clamed catalyst shows a decent open circuit voltage (OCV, ∼1.48V) and a high discharge peak power density (349mWcm−2), corresponding to a coulombic efficiency of 92%. In a rechargeable ZABs with this bifunctional catalyst, high OCV (>1.3V) and small charge-discharge voltage gap (<1.1V) are achieved along with high specific capacity (780mAhg−1 at 30mAcm−2) and robust cycle-life (1,390 cycles at cycle profile of 20mA/10min).

Effects of Land Deals on Peak Discharge and Sediment Transport in the Catchments Around the Grand Ethiopian Renaissance Dam

AbstractLand degradation poses a threat to reservoirs because of siltation; hence, sustainable hydropower development necessitates the conservation of upstream catchments. Ethiopia is currently constructing Africa's largest hydropower dam, the Grand Ethiopian Renaissance Dam (GERD), on the Blue Nile. Given the commercialization of large tracts of land in the closer catchments, there is a need to explore the effects on peak discharge and suspended sediment concentration. A field survey was conducted on 20 ephemeral streams to compare annual maximum peak discharges between catchments (0·4 – 15·5 km2), eight of which drain commercial farms and twelve others, land under traditional management. We measured channel characteristics, observed flood marks and applied the empirical Manning equation to calculate peak discharges. SSC samples were taken during each runoff event from a stream in each of the two dominant land management categories. Results indicated that commercial farms contributed for the 51% increase in peak runoff compared to traditionally managed lands. Catchments dominated by commercial farms also have a significantly higher SSC (mean = 6·44 ± 2·23 g l−1) compared to catchments without commercial farms (mean = 2·77 ± 2·31 g l−1). Forests and woodlands have a strong buffering effect upon flood generation while higher peak discharges and sediment transport have generated from crop lands. However, leasing forests and woodland to agricultural companies has resulted in deforestation. Consequently, the increased runoff response may lead to downstream bank erosion and affect downstream communities; the increased sediment transport poses a threat to the multibillion dollar hydropower reservoir of the GERD. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Contribution of river floods, hurricanes, and cold fronts to elevation change in a deltaic floodplain, northern Gulf of Mexico, USA

Deltas are globally important locations of diverse ecosystems, human settlement, and economic activity that are threatened by reductions in sediment delivery, accelerated sea level rise, and subsidence. Here we investigated the relative contribution of river flooding, hurricanes, and cold fronts on elevation change in the prograding Wax Lake Delta (WLD). Sediment surface elevation was measured across 87 plots, eight times from February 2008 to August 2011. The high peak discharge river floods in 2008 and 2011 resulted in the greatest mean net elevation gain of 5.4 to 4.9 cm over each flood season, respectively. The highest deltaic wetland sediment retention (13.5% of total sediment discharge) occurred during the 2008 river flood despite lower total and peak discharge compared to 2011. Hurricanes Gustav and Ike resulted in a total net elevation gain of 1.2 cm, but the long-term contribution of hurricane derived sediments to deltaic wetlands was estimated to be just 22% of the long-term contribution of large river floods. Winter cold front passage resulted in a net loss in elevation that is equal to the elevation gain from lower discharge river floods and was consistent across years. This amount of annual loss in elevation from cold fronts could effectively negate the long-term land building capacity within the delta without the added elevation gain from both high and low discharge river floods. The current lack of inclusion of cold front elevation loss in most predictive numerical models likely overestimates the land building capacity in areas that experience similar forcings to WLD.

3D hollow sphere Co3O4/MnO2-CNTs: Its high-performance bi-functional cathode catalysis and application in rechargeable zinc-air battery

There has been a continuous need for high active, excellently durable and low-cost electrocatalysts for rechargeable zinc-air batteries. Among many low-cost metal based candidates, transition metal oxides with the CNTs composite have gained increasing attention. In this paper, the 3-D hollow sphere MnO2 nanotube-supported Co3O4 nanoparticles and its carbon nanotubes hybrid material (Co3O4/MnO2-CNTs) have been synthesized via a simple co-precipitation method combined with post-heat treatment. The morphology and composition of the catalysts are thoroughly analyzed through SEM, TEM, TEM-mapping, XRD, EDX and XPS. In comparison with the commercial 20% Pt/C, Co3O4/MnO2, bare MnO2 nanotubes and CNTs, the hybrid Co3O4/MnO2-CNTs-350 exhibits perfect bi-functional catalytic activity toward oxygen reduction reaction and oxygen evolution reaction under alkaline condition (0.1 M KOH). Therefore, high cell performances are achieved which result in an appropriate open circuit voltage (∼1.47 V), a high discharge peak power density (340 mW cm−2) and a large specific capacity (775 mAh g−1 at 10 mA cm−2) for the primary Zn-air battery, a small charge–discharge voltage gap and a high cycle-life (504 cycles at 10 mA cm−2 with 10 min per cycle) for the rechargeable Zn-air battery. In particular, the simple synthesis method is suitable for a large-scale production of this bifunctional material due to a green, cost effective and readily available process.

Data assimilation of satellite-based actual evapotranspiration in a distributed hydrological model of a controlled water system

Advances in earth observation (EO) and spatially distributed hydrological modelling provide an opportunity to improve modelling of controlled water systems. In a controlled water system human interference is high, which may lead to incorrect parameterisation in the model calibration phase. This paper analyses whether assimilation of EO actual evapotranspiration (ETa) data can improve discharge simulation with a spatially distributed hydrological model of a controlled water system. The EO ETa estimates are in the form of eight-day ETa composite maps derived from Terra/MODIS images using the ITA-MyWater algorithm. This algorithm is based on the surface energy balance method and is calibrated for this research for a low-lying reclamation area with a heavily controlled water system: the Rijnland area in the Netherlands. Data assimilation (DA) with the particle filter method is applied to assimilate the ETa maps into a spatially distributed hydrological model. The hydrological model and DA framework are applied using the open source software SIMGRO and PCRaster-Python respectively. The analysis is done for a period between July and October 2013 in which a high discharge peak followed a long dry-spell. The assimilation of EO ETa resulted in local differences in modelled ETa compared to simulation without data assimilation, while the area average ETa remained almost the same. The modelled cumulative discharge graphs, with and without DA, showed distinctive differences with the simulation, with DA better matching the measured cumulative discharge. The bias of simulated cumulative discharge to the observed data reduced from 14% to 4% when using DA of EO ETa. These results showed that assimilating EO ETa may not only be effective in the more common applications of soil moisture and crop-growth modelling, but also for improving discharge modelling of controlled water systems.

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.

Impact analysis of flood in Accra, Ghana

Within the past decades, flooding has become a global pandemic, which hampers economic and social development. This global phenomenon has led to loss of lives and economic damages in many countries including Ghana. On June 3rd 2015, Accra, Ghana's capital experienced an unprecedented flash flood event, coupled with an explosion at a Goil filling station that resulted in a death toll of over 152 lives. It is therefore necessary to explore new ideas and approaches that can be incorporated to existing structures to manage this problem. The aim of this study is to analyse the underlying causes of flood in Accra, examine the suitable structural measures that can be undertaken to mitigate flood impacts in Accra, and propose a mitigation approach to manage flood impacts using Integrated Flood Risk Management and Sustainable Flood Management. The Intensity of rainfall events in eight drainage basins in Accra namely; Kpeshie, Korle, Densu, Sakumo, Lafa, Osu, Songo Mokwe and Chemu triggers flash floods due to a short response time and high specific peak discharges. Precipitation patterns in Accra have changed considerably within this few decades. According to IPCC scenario B1, A1B, and A2 forecasting, there will be an increase in the average monthly precipitation from 160 mm in 1991-2010 to 200 mm in 2011-2020 respectively. A ten (10) year flood protection level was employed to model the rate of urban damage, estimate affected Gross Domestic Product (GDP) and the population at risk in Accra

Influence of Rainfall Characteristics on Total Suspended Solids in Urban Runoff: A Case Study in Beijing, China

An urban rainfall-runoff water quality model was developed to simulate total suspend solids (TSS) using the stormwater management model (SWMM) for a 3.8 ha university campus in Beijing (approximately 76.5% impervious), and calibrated and validated against data from two observed rainfall events (221.2 and 16.6 mm rainfall). Model performance is satisfactory (Nash–Sutcliffe model efficiency 0.8 and 0.72 for flow and 0.74 and 0.51 for TSS concentration, respectively). A series of sensitivity model runs were conducted using the calibrated SWMM to study the influences of rainfall characteristics (rainfall hyetographs, depths and durations) and surface flooding on the TSS concentration in outlet runoff of the catchment. The Pilgrim and Cordery rainfall distribution defines a first-quartile storm (the most severe) and results in the highest peak discharge and TSS concentration at the outlet but the lowest outlet TSS load because of the highest TSS flood loss (32.3%). The simulated TSS pollutograph resulting from the Keifer and Chu rainfall distribution (with r = 0.5) is almost identical to that resulting from the alternating block rainfall distribution. Under the same rainfall hyetograph, simulated peak discharge and outlet TSS load are positively correlated (R2 = 0.95) to the rainfall depth as a function of the return period.

Assessing the Hydrological Response of Ayamama Watershed from Urbanization Predicted under Various Landuse Policy Scenarios

This study investigated the effects of urbanization predicted using the SLEUTH urban growth model (an acronym taken from Slope, Landuse, Exclusion, Urban extent, Transportation and Hillshade) under four landuse policy scenarios on the hydrological response of Ayamama watershed using the Hydrologic Engineering Center Release 1 (HEC-1) hydrological model. The SLEUTH model was calibrated based on the Brute Force Monte Carlo iteration technique using the urban extents of Istanbul in 1987, 2000, 2009 and 2013 and was verified by considering Kappa coefficient as evaluation criteria. HEC-1 was calibrated and verified using observed rainfall-runoff event and based on the coefficient of determination (R2), Nash-Sutcliffe coefficient of efficiency (CE) and percentage of bias (PBIAS) as performance indicators. The urbanization prediction results showed that the urban extent of Ayamama watershed would reach 50.3 km2, 44 km2, 63 km2 and 60 km2 under Scenarios 1, 2, 3 and 4, respectively, in 2050. The hydrological simulation results under these urban extents showed that the urban extent of Ayamama watershed under Scenario-3, a scenario that allows unrestricted growth with the implementation of Project Canal Istanbul (PCI), resulted in the highest peak discharge and the shortest time to peak. Such an increase in the peak discharge and reduction in the time to peak will increase the risk of flooding and, therefore, extreme care needs to be taken before and during the implementation of PCI.

Co(II)1-xCo(0)x/3Mn(III)2x/3S Nanoparticles Supported on B/N-Codoped Mesoporous Nanocarbon as a Bifunctional Electrocatalyst of Oxygen Reduction/Evolution for High-Performance Zinc-Air Batteries.

Rechargeable Zn-air battery is an ideal type of energy storage device due to its high energy and power density, high safety, and economic viability. Its large-scale application rests upon the availability of active, durable, low-cost electrocatalysts for the oxygen reduction reaction (ORR) in the discharge process and oxygen evolution reaction (OER) in the charge process. Herein we developed a novel ORR/OER bifunctional electrocatalyst for rechargeable Zn-air batteries based on the codoping and hybridization strategies. The B/N-codoped mesoporous nanocarbon supported Co(II)1-xCo(0)x/3Mn(III)2x/3S nanoparticles exhibit a superior OER performance compared to that of IrO2 catalyst and comparable Zn-air battery performance to that of the Pt-based battery. The rechargeable Zn-air battery shows high discharge peak power density (over 250 mW cm(-2)) and current density (180 mA cm(-2) at 1 V), specific capacity (∼550 mAh g(-1)), small charge-discharge voltage gap of ∼0.72 V at 20 mA cm(-2) and even higher stability than the Pt-based battery. The advanced performance of the bifunctional catalysts highlights the beneficial role of the simultaneous formation of Mn(III) and Co(0) as well as the dispersed hybridization with the codoped nanocarbon support.

Morphology controlled La2O3/Co3O4/MnO2–CNTs hybrid nanocomposites with durable bi-functional air electrode in high-performance zinc–air energy storage

In this paper, both primary and rechargeable Zn–air batteries are constructed using La2O3/Co3O4/MnO2–CNTs hybrid nanocomposites as air electrodes for high-performance energy storage and conversion. The air electrode hybrid catalysts with controlled morphology are prepared by a facile hydrothermal self-assembly process, which exhibits highly bi-functional catalytic activity for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) during discharge and charge processes in a rechargeable Zn–air battery. When these catalysts are integrated into a practical primary Zn–air battery, a high open circuit voltage of 1.5V is achieved along with a high discharge peak power density of 295mWcm−2. The specific capacity normalized to the mass of consumed Zn is 821mAhg−1, corresponding to a high energy density of 970Whkg−1, which shows this zinc–air battery’s performance is higher than any battery currently commercially available to meet the requirements of high-power electric equipment. More specifically, the electrochemically rechargeable Zn–air battery incorporating by this bifunctional catalyst exhibits an unprecedented small charge–discharge voltage polarization, high reversibility and high stability, suggesting this battery can be used as a power source for portable electronics, armamentarium and electrical vehicles. Furthermore, a flexible, rechargeable Zn–air battery as a wholly solid-state energy storage device, and exhibiting good peak power density and decent stability, should be viable in other practical applications such as smart electronics and wearable electronic devices.