Electrolytic Oxygen Research Articles

Nucleation bubble boundary layer theory for ultra-fast electrochemical polishing of additive manufacturing components

The application of electrochemical-based polishing techniques, including electrochemical polishing (ECP) and plasma electrolytic polishing (PEP), to improve the surface quality of additive manufacturing (AM) components is challenged by the high amplitudes and long spatial wavelengths of roughness, which cause pre-polishing procedures to be indispensable. In this study, a nucleation bubble boundary layer (NBBL) mechanism for enhanced electrochemical-based polishing performance is revealed to solve this problem, namely nucleation bubble electrochemical polishing (NBEP). The NBBL is constructed on the anode surface via electrolytic oxygen evolution and nucleate boiling, and is activated by regulating the temperature and electric potential. The experiments verify a model of NBBL consisting of an inner adherent layer and outer diffusion layer (ODL). Simulations and experiments demonstrate that the polishing mechanism is based on the combined current-limiting effect of individual adherent bubbles and the ODL, which differentiates the anodic dissolution rates at the peaks and valleys of a wide range of spatial wavelengths with their electrical resistance. The bubble dynamics also enhance mass transfer, further improving the polishing efficiency. The experimental results show that NBEP is capable of reducing the surface roughness of AM stainless steel 316 L from Ra of 10.22 μm to 0.71 μm, and eliminating the spatial wavelengths of 200–400 μm in 8 min, which cannot be achieved by either ECP or PEP. The polishing current density also increased from 0.25 (ECP) and 0.48 (PEP) to 2 A/cm2 in NBEP. Finally, a prediction model that accurately describes the ultimate roughness achieved by NBEP as a function of the minimum cavity size is established. The NBEP can be directly followed by PEP or ECP to achieve an optimal surface finish of Ra <70 nm for AM parts. The NBEP method considerably enhances the polishing performance of electrochemical-based systems for AM components, as well as expands the application range of electrochemical-based polishing techniques.

Investigating the Role of Byproduct Oxygen in UK-Based Future Scenario Models for Green Hydrogen Electrolysis

Water electrolysis for hydrogen production with renewable electricity is regularly studied as an option for decarbonised future energy scenarios. The inclusion of byproduct electrolytic oxygen capture and sale is of interest for parallel decarbonisation efforts elsewhere in the industry and could contribute to reducing green hydrogen costs. A deterministic hydrogen electrolysis system model is constructed to compare oxygen inclusion/exclusion scenarios. This uses wind and solar-PV electricity generation timeseries, a power-dependent electrolysis model to determine the energy efficiency of gas yield, and power allocation for gas post-processing energy within each hourly timestep. This maintains a fully renewable (and therefore low/zero carbon) electricity source for electrolysis and gas post-processing. The model is validated (excluding oxygen) against an existing low-cost GW-scale solar-hydrogen production scenario and an existing hydrogen production costs study with offshore wind generation at the multi-MW scale. For both comparisons, oxygen inclusion is then evaluated to demonstrate both the benefits and drawbacks of capture and utilisation, for different scenario conditions, and high parameter sensitivity can be seen regarding the price of renewable electricity. This work subsequently proposes that the option for the potential utilisation of byproduct oxygen should be included in future research to exemplify otherwise missed benefits.

Elevated temperature-driven coordinative reconstruction of an unsaturated single-Ni-atom structure with low valency on a polymer-derived matrix for the electrolytic oxygen evolution reaction.

A high-temperature pyrolysis-controlled coordination reconstruction resulted in a single-Ni-atom structure with a Ni-Nx-C structural unit (x = N atom coordinated to Ni). Pyrolysis of Ni-phen@ZIF-8-RF at 700 °C resulted in NiNP-NC-700 with predominantly Ni nanoparticles. Upon elevating the pyrolysis temperature from 700 to 900 °C, a coordination reconstruction offers Ni-Nx atomic sites in NiSA-NC-900. A combined investigation with X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and soft X-ray L3-edge spectroscopy suggests the stabilization of low-valent Niδ+ (0 < δ < 2) in the Ni-N-C structural units. The oxygen evolution reaction (OER) is a key process during water splitting in fuel cells. However, OER is a thermodynamically uphill reaction with multi-step proton-coupled electron transfer and sluggish kinetics, due to which there is a need for a catalyst that can lower the OER overpotentials. The adsorption energy of a multi-step reaction on a single metal atom with coordination unsaturation tunes the adsorption of each oxygenated intermediate. The promising OER activity of the NiSA-NC-900/NF anode on nickel foam was followed by the overall water splitting (OWS) using using NiSA-NC-900/NF as anode and Pt coil as the cathodic counterpart, wherein a cell potential of 1.75 V at 10 mA cm-2 was achieved. The cell potential recorded with Pt(-)/(+)NiSA-NC-900/NF was much lower than that obtained for other cells, i.e., Pt(-)/NF and NF(-)/(+)NF, which enhances the potentials of low-valent NiSAs for insightful understanding of the OER. At a constant applied potential of 1.61 V (vs.RHE) for 12 h, an small increase in current for initial 0.6 h followed by a constant current depicts the fair stability of catalyst for 12 h. Our results offer an insightful angle into the OER with a coordinatively reconstructed single-Ni-atom structure at lower valency (<+2).

Evaluation limit of O2 permeability in barrier films by electrolytic oxygen pump

Packaging foods, medicines, and electronic devices and shielding them with barrier films to protect them from oxidation and degradation are crucial technologies for their long-term preservation. In this paper, a new evaluation device and the evaluation limit of oxygen transmission rate (OTR) in barrier films were described. The device was based on an O2 pump, consisting of the cathode reaction of a fuel cell (absorbing O2) and the anode reaction of water electrolysis (generating O2). By shielding the cathode with barrier films, the reaction current was strictly determined by the permeated O2 through the barrier film. OTRs in typical polymer films such as silicon rubber, polyethylene, and polyester were evaluated to confirm the method was consistent with conventional methods. The detection limit for high barrier films was examined and found to be approximately 10 cc/m2/day/atm at the present stage. The strategies to improve the detection limit were discussed.

Magnetically-Induced Buoyancy for Efficient Electrochemical Oxygen Production in Microgravity

The realization of long-term space travels and the establishment of a lunar research platform are challenged by the lack of technological device architectures for efficient, stable and continuous oxygen production. One obstacle is that the near-absence of buoyancy in microgravity results in hindered gas bubble desorption at the electrode-electrolyte interface, causing lower efficiencies for electrolyser systems when operating in space.1,2 The significantly reduced buoyancy force also has severe complications for phase separation, which is a crucial process for a variety of space technologies also including heat transfer, fuel production and removal of carbon dioxide from cabin air. Multiple approaches have been studied in the past to induce phase separation such as creating centrifugal force fields. These approaches lack however efficiency, stability and robustness.3,4 In our recent work, we demonstrate the use of magnetic polarisation to artificially induce buoyancy in the electrolytic oxygen evolution half-cell reaction and thus significantly increasing the overall half-cell efficiency. This was carried out in a series of experiments at the Bremen Drop Tower, Center of Space Technology and Microgravity (ZARM, Germany), where short-term microgravity conditions of 9.2 s were achieved.5,6. Chronoamperometric and cyclic voltammetry measurements on high-activity RuOx electrocatalyst structures on a Ti substrate were undertaken with and without a magnet in close proximity to the electrode to closely monitor the electrochemical performance in a three-electrode potentiostatic arrangement and to demonstrate the magnetic effect on gas bubble desorption during free fall. It was observed that current densities for the electrodes at a potential of +1.49 V vs RHE were significantly higher in the presence of a magnet. We conclude that magnetic phase separation can be utilised in electrolytic systems in reduced gravitational environments to efficiently detach oxygen bubbles from the electrode surface and operate the devices at higher efficiencies, providing a key advancement for future oxygen production in space missions.2,3,5 References Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. (2018). Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Lett., 3, 1795−1800.Saravanabavan, S.; Coulthard, C. T.; Kaur, M.; Brinkert, K. (2022). Catalysis in Space Environments. doi.org/10.1002/9783527830909.ch7 In: Hessel V., Stoudemire J., H. Miyamoto & I. D. Fisk (Eds.). In Space Manufacturing and Resources.Wiley-VCH. ISBN: 978-3-527-83091-6Romero-Calvo, Á.; Akay, Ö.; Schaub, H.; Brinkert, K. (2022). Magnetic phase separation in microgravity. npj Microgravity 8 (32). doi.org/10.1038/s41526-022-00212-9.Harvey, A.; Ramshaw, C.; Reay, D. A. Process Intensification: Engineering for Efficiency. Sustainability and Flexibility. 2nd edition. Butterworth- Heinemann; 201Brinkert, K.; Richter, M. H.; Akay, Ö.; Liedtke, J.; Giersig, M.; Fountaine, K. T.; Lewerenz, H. J. (2018). Efficient solar hydrogen production in microgravity environment. Commun. 9(2527). doi: 10.1038/s41467-018-04844-yhttps://www.zarm.uni-bremen.de/fileadmin/user_upload/drop_tower/Users_Manual_0412.pdf

Robust electrolytic oxygen evolution at nanostructured NiFe LDH@ in-situ functionalized graphite felt

NiFe layered double hydroxide (LDH) is among the most effective electrocatalysts for oxygen evolution reaction (OER). Tailor-designed NiFe LDH with high electronic conductivity assists in facile hydrogen production with marked energy-saving. Graphite felt (GF), a 3-D porous substrate with excellent conductivity is used herein. However, its low hydrophilicity calls for pretreatment. Herein, the potential strength of electrochemistry is applied to enhance the hydrophilicity of GF surface during the deposition of homogenous uniform distributed NiFe LDH electrocatalyst. GF is sequentially modified by sweeping the potential from the oxidative to the reductive region in a solution containing 100 mM NiSO4 and 30 mM FeCl3. Carbon structure flaws are introduced at the positive potential region. whereas during the negative potential scan, hydrogen evolution occurs with simultaneous uniform and homogeneous deposition of NiFe LDH. SEM, HR-TEM, mapping EDX, XPS, XRD, and contact angle measurements are utilized to reveal the features of the functionalized GF with NiFe LDH deposits. Furthermore, FeOOH/GF and Ni(OH)2/GF electrodes are prepared to highlight the advantages of the binary NiFe LDH/GF electrode toward the OER. Interestingly, the NiFe LDH/GF enhances the OER in an alkaline medium by throwing up a low overpotential of 273 mV to support a current density of 10 mA cm−2 alongside a Tafel slope of 48.5 mV dec−1. Furthermore, the NiFe LDH shows marked stability for 24 h of ongoing electrolysis. Therefore, the designed catalyst can be worked as an efficient anode for water electrolysis.

Construction of an electrode with hierarchical three-dimensional NiFe-oxyhydroxides by two-step electrodeposition for large-current oxygen evolution reaction

Oxygen evolution reaction (OER) electrocatalysts are promised to be extremely important in hydrogen generation of water electrolysis as one of the renewable energy technologies. However, low efficiency and high cost are two crucial barriers that hinder its development and application. Herein, we developed highly efficient NiFe-based self-supported electrocatalysts by a facile two-step electrodeposition method focusing on the porosification of a nickel foam (NF) substrate. The porous nickel layer (PN/NF) formed in the first step by dynamic hydrogen bubble template electrodeposition proved to be effective in facilitating the mass transfer process, and the following second step of nickel-iron deposition (NiFe/PN/NF) continued to increase the intrinsic catalytic activity, with the two synergistically contributing to the excellent OER performance. As an oxygen evolution electrode, it exhibits high catalytic activity in alkaline water electrolysis, which requires only an overpotential of 211 mV to promote the oxidation reaction of water. The overpotentials for the OER at 100, 500 and 750 mA cm−2 are as low as 244, 297 and 326 mV in 1 M KOH, respectively. In 6 M KOH, the overpotentials for driving electrolytic oxygen production at 100, 500, 750 and 1000 mA cm−2 are even lowered spectacularly to 133 mV, 178 mV, 193 mV and 208 mV, respectively. In particular, the catalyst showed a catalytic stability of more than 40 h at a current density of 500 mA cm−2, which presents it as a highly promising candidate for future large-scale industrial applications.

Techno-economic analysis of sustainable methanol and ammonia production by chemical looping hydrogen generation from waste plastic

In this work, a techno-economic analysis on a novel plant configuration achieving the combined production of ammonia and methanol through chemical looping has been carried out. The innovative process presents advantages in terms of reduced dependency on market price fluctuations, thanks to the combined production of two chemicals, and optimal utilization of the chemical looping gases. The chemical looping plant is fed with recycled high density polyethylene to enhance the carbon circularity of the process. In this case, part of the captured CO2 is employed for methanol production along with hydrogen from chemical looping, while hydrogen from electrolysis is used for ammonia production by reaction with nitrogen from the air reactor. Renewable electric energy supply ensures a carbon free power to fuel conversion. Several sensitivity analyses were carried out to assess the optimum process parameters combination, i.e. fuel flow rate, steam flow rate, oxygen carrier inlet temperature. The final production rate is divided between 174 kg/h of methanol and 910 kg/h of ammonia. An economic analysis was then carried out. A capital cost of 27 M€ and an operating cost of 3 M€/y were computed. Sensitivity analyses on the impact of the electricity input cost, the electrolytic oxygen selling price, the electrolyser capital cost and the internal rate of return were carried out. The electricity demand was discovered to impact for the 68% of the total operating costs. For an electricity cost of 0.03 €/kWh, oxygen selling price of 0.07 €/kgO2 and internal rate of return of 8%, a final products cost of 0.76 €/kg was then determined. The process achieves specific CO2 emissions of 0.017 kgCO2/kgprd, which is significantly lower than the traditional processes (0.24 kgCO2/kgCH3OH and 1.66 kgCO2/kgNH3), and an energy intensity of 36 GJ/tprd. The final selling price of the products is still not competitive with the traditional processes but is comparable with ammonia production from electrolysis and air separation and methanol production from electrolysis and direct air capture.

Integrated Valve Product Fluid Simulation and Test Verification

The integrated valve product’s main function is to electrolytic oxygen generation subsystem to produce hydrogen and oxygen to realize automatic discharge, to maintain the space station astronauts in orbit around in comfort and safety, high reliability, easy maintenance, and the device should be easy replacement of human-computer ergonomics requirements to ensure long-term on-orbit operation station. Based on the above requirements, an integrated valve product based on environmental control and a health protection system is designed. The integrated product includes hydrogen normal and backup emission branches, oxygen normal and backup emission branches. Through fluid simulation and experimental verification, it is verified that the flow rate and other key indicators of the integrated valve product meet the requirements, which has certain reference and guiding significance for the design of similar integrated products in the future.

Production of Substitute Natural Gas Integrated with Allam Cycle for Power Generation

The accumulation of energy from non-programmable renewable sources is a crucial aspect for the energy transition. Using surplus electricity from renewable energy sources, power-to-gas plants allow to produce a substitute natural gas (SNG) that can be injected in the existing infrastructure for large-scale and long-term energy storage, contributing to gas grid decarbonisation. The plant layout, the method used for carbon dioxide capture and the possible cogeneration of electricity can increase the efficiency and convenience of SNG synthesis plants. In this work, a system for the simultaneous production of SNG and electricity starting from biomass and fluctuating electricity from renewables is proposed, using a plant based on the Allam thermodynamic cycle as the power unit. The Allam power cycle uses supercritical CO2 as evolving fluid and is based on the oxycombustion of gaseous fuels, thus greatly simplifying CO2 capture. In the proposed system, oxycombustion is performed using biomass syngas and electrolytic oxygen. The CO2 generated by means of oxycombustion is captured, and it is subsequently used together with renewable hydrogen for the production of SNG through thermochemical methanation. The system is also coupled with a solid oxide electrolyser and a biomass gasifier. The whole plant was analysed from an energy-related point of view. The results show overall plant efficiency of 67.6% on an LHV basis (71.6% on an HHV basis) and the simultaneous production of significant amounts of electricity and of high-calorific-value SNG, whose composition could be compatible with the existing natural gas network.

Design and economic analysis of an on-site electrolytic medical oxygen and solar electricity production system in a sunny country

The present work is focused on the technical and economic feasibility of on-site electricity and medical electrolytic oxygen production system. The system sized to satisfy an oxygen and electricity demand respectively close to 20 m3 per day and 600.5 kWh per day, consists of a 61 kW photovoltaic farm, a 17 kW alkaline main electrolyzer, a 15 kW auxiliary electrolyzer, and a 37 kW fuel cell used as a backup power source. The main energy source was sized with the objective to maintain the loss of load probability lower than 8 %. The net present value was used as the economic metric to perform the profitability analysis. The system sized was simulated under intermittent atmospheric conditions in a well-sunny country. An amount of oxygen around 39.8 m3/day and 15.3 m3/day are produced respectively during the sunniest and the least sunny day. Concerning hydrogen, an amount of 84.2 m3/day and 30.5 m3/day are output by electrolyzer respectively during the sunniest and the least sunny day. For economic analysis, the selling cost of oxygen and electricity was fixed at 8.31 $/m3 and 0.156$/kWh, the current market values in Cameroon. The profitability of the proposed system is expected 60 months after the start under the high-cost projection scenario and after 48 months under the median cost projection scenario. For an optimistic low-cost projection scenario, the NPV is positive after 20 months and a value of 457 k$ is recorded at the end of the lifetime. Finally, the impact of tax legislation and future electricity selling cost on system profitability was also assessed and discussed.

Green electricity and medical electrolytic oxygen from solar energy - A sustainable solution for rural hospitals

The objective of this paper is to design and simulate for rural areas isolated from the electricity grid, a system based on solar energy for the optimal supply of green electricity and medical oxygen to a hospital. The system sized to produce 20 Nm3/day is constituted of a 37.46 kW photovoltaic farm, a 15.47 kW electrolyzer, and a 15.47 kW fuel cell. The simulation of the Photovoltaic system is performed using the single diode model solved with the Lambert function defined in MATLAB Software. The daily production of oxygen and hydrogen during the sunniest day of the month is respectively 20.81 Nm3/day and 41.61 Nm3/day. The daily energy that can be stored is relevant to the hydrogen production and an electricity storage capacity of 124.89 kWh is feasible. During the least sunny day of the least sunny month, the daily production of oxygen and hydrogen is respectively, 7.72 Nm3/day and 15.44 Nm3/day. The recorded values prove that the system sized can constitute a viable solution to ensure the permanent supply a green electricity and oxygen to the hospital with good energy storage capacity.

Single-Step Synthesis of Fe-Doped Ni3S2/FeS2 Nanocomposites for Highly Efficient Oxygen Evolution Reaction.

Due to the sluggish kinetic reaction, the electrolytic oxygen evolution reaction (OER) is one of the obstacles in driving overall water splitting for green hydrogen production. In this study, we demonstrate a strategy to improve the OER performance of Ni3S2. The effect of addition of different FeCl2 contents during the hydrothermal process on the OER activity is systematically evaluated. We found that all samples upon the addition of FeCl2 produced Fe-doped Ni3S2 and FeS2 to form a nanocomposite. Their OER performances strongly depend on the amount of FeCl2, where the NSF-0.25 catalyst with 0.25 mmol FeCl2 added during the hydrothermal synthesis shows the best OER performance. Its overpotential was 230 mV versus RHE and it achieves a high current density of 100 mA·cm-2, which was much lower than that of pristine Ni3S2 (320 mV) or RuO2 (370 mV) as the benchmark OER catalyst. The postcharacterizations reveal that NSF-0.25 has gone through an in situ phase transformation into an Fe-NiOOH phase during the OER test. This study presents a simple method and a low-cost material to improve the OER performance with in situ formation of oxyhydroxide.

In situ generated oxygen distribution causes maturity differentiation during electrolytic oxygen aerobic composting

Electrolytic oxygen aerobic composting (EOAC) is an effective treatment with greater technical superiority and cost advantages for organic solid waste using in situ electrolytic oxygen as a feasible strategy to replace conventional aeration. However, the unclear effects of distribution and variation of in situ electrolytic oxygen on compost maturation in different depth zones of EOAC need further exploration. This study demonstrated that the humification of organic matter was faster at the bottom than in the middle and at the top. The main reason was that the higher oxygen content and lower moisture content in the bottom promoted microbial degradation and heat production, resulting in higher temperatures. The microbial analysis showed that the abundance of typical thermophilic bacteria (such as Cerasibacillus, Lactobacillus, and Pseudogracilibacillus) that could promote compost maturation was higher at the bottom than in the middle and at the top. The finding provided in-depth molecular insights into differentiated humification from bottom to top in EOAC and revealed its further practical engineering applications.

Deciphering the structural characteristics and molecular transformation of dissolved organic matter during the electrolytic oxygen aerobic composting process

Electrolytic oxygen aerobic composting (EOAC) effectively treats organic solid waste by using in-situ electrolytic oxygen for aeration. However, the fundamental mechanism of compost maturity is still unclear. Therefore, we comprehensively characterized dissolved organic matter (DOM) transformation closely related to compost maturity during EOAC. Excitation-emission matrix-parallel factor (EEM-PARAFAC) and Fourier transform infrared (FTIR) analysis confirmed that EOAC quickly decreased organic matter and increased humus substances, accelerating the compost humification process compared with conventional aerobic composting. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis reveals that the double bound equivalent and aromaticity index during EOAC are higher than in conventional aerobic composting (CAC), suggesting more aromatic compounds in EOAC. DOM's detailed transformation investigation suggested that low O/C and high H/C compounds were preferentially decomposed during EOAC. Our investigation firstly extends the in-depth molecular mechanisms of humification during EOAC, and reveals its practical engineering applications.

Construction of CoNiFe Trimetallic Carbonate Hydroxide Hierarchical Hollow Microflowers with Oxygen Vacancies for Electrocatalytic Water Oxidation

AbstractIt is of great challenge to design transition multimetallic carbonate hydroxides with delicate hollow features and defects for efficient electrolytic oxygen evolution reaction (OER). Here, a sequential self‐templating method to synthesize CoNiFe trimetallic carbonate hydroxide hierarchical hollow microflowers (CN‐xFe HMs) with oxygen vacancies (VO) is reported. The synergistic merits of hollow structure, Fe substitution, and VO endow the CN‐xFe HMs with high active‐site exposure density and increased electrical conductivity. Specially, the optimized CN‐xFe HMs validate the excellent OER performance with an overpotential of 258 mV to drive 10 mA cm−2 and a Tafel slope of 48.7 mV dec−1. Theoretical calculations reveal that Fe substitution and VO can synergistically regulate the electronic states to achieve near‐ideal adsorption/desorption capacity for oxygenated intermediates. Moreover, the successful synthesis of other six metals substituted CoNiM (M = Cu, Zn, Cr, Mo, Er and La) carbonate hydroxides provides a universal protocol to construct transition multimetallic electrocatalysts with hollow structures for gaining highly efficient energy conversion reactions.

Decarbonization of cement production in a hydrogen economy

The transition to net-zero emission energy systems creates synergistic opportunities across sectors. For example, fuel hydrogen production from water electrolysis generates by-product oxygen that could be used to reduce the cost of carbon capture and storage (CCS) essential in the decarbonization of clinker production in cement making. To assess this opportunity, a techno-economic assessment was carried out for the production of clinker using oxy-combustion in a natural gas-fueled plant coupled to CCS. Material and energy flows were assessed in a reference case for clinker production (oxygen from air, no CCS), and compared to oxy-combustion clinker production from either an air separation unit (ASU, 95% O2), or water electrolysis (100% O2), both coupled to CCS. Compared to the reference, air-combusted clinker plant, oxy-combustion increases thermal energy demand by 7% and electricity demand by 137% for ASU and 67% for electrolytic oxygen. The levelized cost of oxygen supply ranges from $49/tO2 for an on-site ASU to pipelined electrolytic O2 at $35/tO2 (200 km) or $13/t O2 (20 km). The cost of clinker for the reference plant without CCS increases linearly from $84/t clinker to $193/t clinker at a carbon price of $0/tCO2 to $150/tCO2, respectively. With oxy-combustion and CCS, the clinker production cost ranges from $119 to $122/t clinker, reflecting a breakeven carbon price of $39 to $53/tCO2 compared to the reference case. The lower cost for the electrolytic supply of by-product oxygen compared to ASU oxygen must be balanced against the reliability of supply, the pipeline transport distance and the charges that may be added by the hydrogen producer.

Boosting electrocatalysis of oxygen reduction and evolution reactions with cost-effective cobalt and nitrogen-doped carbons prepared by simple carbonization of ionic liquids

Development of cost-effective, bi-functional carbon electrocatalysts via direct carbonization of ionic liquids (bis(cholinium) tetrachlorocobaltate(II) ([Ch] 2 [CoCl 4 ]) and bis(1-butyl-3-methylimidazolium) tetrachlorocobaltate(II) ([Bmim] 2 [CoCl 4 ])) is reported herein for the first time. Carbon electrocatalysts, dual-doped with cobalt and nitrogen, were tested for oxygen reduction (ORR) and oxygen evolution (OER) reactions. Both materials show high bi-functional catalytic activity and excellent stability due to synergistic effects arising from the presence of nitrogen and cobalt. Electrocatalyst prepared by carbonization of [Ch] 2 [CoCl 4 ] show exceptional activity and selectivity toward ORR. Conversely, electrocatalyst prepared from [Bmim] 2 [CoCl 4 ] showed a slightly better OER performance indicating that different catalytic sites are responsible for O 2 reduction and H 2 O oxidation. Parent CoO particles with graphitic nitrogen boost activity for ORR, while elemental Co supported by nitrogen atoms is responsible for OER activity. Finally, energy consumption during electrolytic oxygen production was calculated revealing energy saving when using two materials as anode electrocatalysts. • Co,N dual-doped carbons are prepared by direct carbonization of ionic liquids. • A next-level of bi-functional electrocatalysts are developed for ORR and OER. • C Ch shows superior electrocatalytic performance for ORR with transfer of 4 e−. • Materials display high OER efficiencies with Tafel slope as low as 115 mV dec −1 . • Different highly active catalytic sites are responsible for efficient ORR and OER.

Mechanistic Insights into the Interplay between Ion Intercalation and Water Electrolysis in Aqueous Batteries.

Improving electrolyte stability to suppress water electrolysis represents a basic principle for designing aqueous batteries. Herein, we investigate counterintuitive roles that water electrolysis plays in regulating intercalation chemistry. Using the NaxFe[Fe(CN)6]∥NaTi2(PO4)3 (x < 1) aqueous battery as a platform, we report that high-voltage overcharging can serve as an electrochemical activation approach to achieving concurrent Na-ion intercalation and an electrolytic oxygen evolution reaction. When the cell capacity is intrinsically limited by deficient cyclable Na ions, the electrolytic water oxidation on the cathode allows for extra Na-ion intercalation from the electrolyte to the NaTi2(PO4)3 anode, leading to a major increase in cyclable Na ions and specific capacity. The parasitic oxygen generation and potential transition-metal dissolution, as proved by our synchrotron and imaging tools, can be significantly mitigated with a simple reassembling approach, which enables stable electrochemical performance and sheds light on manipulating ion intercalation and water electrolysis for battery fast charging and recycling.

Predicting the efficiency of oxygen-evolving electrolysis on the Moon and Mars

Establishing a permanent human presence on the Moon or Mars requires a secure supply of oxygen for life support and refueling. The electrolysis of water has attracted significant attention in this regard as water-ice may exist on both the Moon and Mars. However, to date there has been no study examining how the lower gravitational fields on the Moon and Mars might affect gas-evolving electrolysis when compared to terrestrial conditions. Herein we provide experimental data on the effects of gravitational fields on water electrolysis from 0.166 g (lunar gravity) to 8 g (eight times the Earth’s gravity) and show that electrolytic oxygen production is reduced by around 11% under lunar gravity with our system compared to operation at 1 g. Moreover, our results indicate that electrolytic data collected using less resource-intensive ground-based experiments at elevated gravity (>1 g) may be extrapolated to gravitational levels below 1 g.