Electrolysis Conditions Research Articles

(Invited, Digital Presentation) Regulating the Dynamic Surface Reconstruction of a Layered Cobalt Oxide Electrocatalyst for Water Oxidation

Water electrolysis conditions accelerate the dissolution and corrosion of electrocatalysts, changing their surface and/or bulk composition/structure from the original states. This dynamic reconstruction process redefines the catalytically active species. However, rational control of the in-situ surface reconstruction for electrocatalysts is tremendously challenging. Here, we proposed a novel redox-tuning method to precisely modulate the surface reconstruction and to favor the water oxidation activity. For a category of layered transition metal oxide (AMO2: A = alkaline metal, M = transition metal), redox of transition metal during the alkaline OER was in-situ tuned to engineer the catalyst leaching potential, manipulate the cation leaching amount, and redirect the dynamic catalyst reconstruction. Specifically, Cl doping lowered the cobalt valence state of LiCoO2 and the further OER potential for its in-situ cobalt oxidation triggering Li leaching. Operando XAFS and DFT calculations confirmed that such modulation bypassed the less favorable surface reconstruction by forming Li1-xCo2O4-type spinel structure, transforming the surface of LiCoO1.8Cl0.2 into a more catalytically-active (oxy)hydroxide phase. The proposed method could be potentially generalized to manipulate the surface reconstruction of other pre-catalysts.

Ex-Situ Investigation of Membrane Swelling in an Electrolyzer Using X-Ray Tomography

In this contribution, we focus on the membrane swelling of a catalyst coated Nafion© 212 in the compound of a polymer electrolyte membrane electrolyzer. So far, the swelling of the catalyst coated membrane (CCM) is mostly investigated isolated from the surrounding components as porous transport layers (PTL) and the flow field plates[1-4]. To explore the swelling, ex-situ tests were carried out, using a special device [5] to control contact pressure and compression and computer tomography. This allowed the swelling of the CCM to be studied at different positions in the structure and at different compression pressures as well as the interaction of the different components. Figure 1 shows a comparison of the dry (a) and (c) and flooded (b) and (d) state of the CCM. The black lines indicate the surface of the CCM. In the flooded state, the thickness of the CCM increases by 20 % from about 50 µm to 60 µm, while the distance of the expanded metal sheets stays constant. This means, that the thickness increase of the CCM results in a decrease of at least one PTL thickness. One main goal of the experiment was to show, whether the swelling of the membrane is dependent or independent of the compression pressure and therefore may cause a different water uptake, which might give an explanation of the decreasing high frequency resistance with increasing pressure [4, 6].[1] Ito, H., Maeda, T., Nakano, A., & Takenaka, H. (2011). Properties of Nafion membranes under PEM water electrolysis conditions. International journal of hydrogen energy, 36(17), 10527-10540[2] Budinski, M. K., & Cook, A. (2010). Osmotic pressure of water in Nafion®. Tsinghua Science & Technology, 15(4), 385-390[3] Kusoglu, A., Kienitz, B. L., & Weber, A. Z. (2011). Understanding the effects of compression and constraints on water uptake of fuel-cell membranes. Journal of the Electrochemical Society, 158(12), B1504[4] Borgardt, E., Giesenberg, L., Reska, M., Müller, M., Wippermann, K., Langemann, M., Lehnert, W., & Stolten, D. (2019). Impact of clamping pressure and stress relaxation on the performance of different polymer electrolyte membrane water electrolysis cell designs. International journal of hydrogen energy, 44(42), 23556-23567[5] Hoppe, E., Janßen, H., Müller, M., & Lehnert, W. (2021). The impact of flow field plate misalignment on the gas diffusion layer intrusion and performance of a high-temperature polymer electrolyte fuel cell. Journal of Power Sources, 501, 230036[6] Stähler, M., Stähler, A., Scheepers, F., Carmo, M., Lehnert, W., & Stolten, D. (2020). Impact of porous transport layer compression on hydrogen permeation in PEM water electrolysis. International journal of hydrogen energy, 45(7), 4008-4014 Figure 1

(Invited) Anion Exchange Membrane and Ionomer Development for Electrochemical CO2 Reduction

Recent developments have proven the economic potential of electrochemical reduction of CO2 to value added chemicals, where single cells are now capable of achieving high energetic efficiencies at industrially relevant current densities. 1 These advances are in no small part due to the increased ionic conductivity, hydroxide stability and commercial availability of anion exchange membranes (AEMs). However, there currently exists little understanding as to how these materials affect the efficiency of CO2 conversion devices because the research community is only now beginning to understand the variety and complexity of the transport processes involved. 2 In collaboration with Ionomr Innovations Inc. and the National Research Council of Canada, and as part of the Energy for Clean Materials Challenge Program, we have made advances in the understanding of how AEM properties affect device performance and how we can develop materials tailor-made for CO2 electrolyser technology.Here, we demonstrate the development of a zero-gap single cell design, utilizing first generation Aemion® materials for the conversion of CO2 to CO with an energetic efficiency of 40% at 200 mA cm-2. 3 Despite the initially high energetic efficiency, we demonstrate how the crossover of carbonate dianions results in the reduction of anolyte pH and deconvolute how this results in a diminished cell efficiency over extended operation. From this, we show how functionalization of the polymer electrolyte structure can reduce this degradation mechanism while retaining high energetic efficiencies.In addition, we demonstrate how under milder electrolysis conditions, the total cell efficiency has a significant dependency on the flux of alkali metal cationic species from the supporting anolyte to the cathode. We show that due to the large promotion effect of cations for the electrochemical CO2 reduction, AEM design not only influences ohmic resistances in the cell, but also greatly affects the charge transfer resistance (RCT) of the cathode to a much greater extent than other electrochemical conversion devices. We thus make correlations between water permeability and perm-selectivity of AEMs to the overall CO2 conversion efficiency.We then discuss the incorporation of anion exchange ionomers in the cathode catalyst layer of CO2 electrolysis cells and how the ionomer parameters define the efficiency and selectivity of Ag catalysts towards electrochemical CO2 reduction. Through this work, we demonstrate the influencing factors of AEM and ionomer materials on the efficiency of electrochemical CO2 conversion and conclude that further advances are paramount for the adoption of this promising technology, which is integral in closing the carbon loop of the petrochemical industry and meeting our wider climate change targets.

Cu As Co-Catalyst for the Photo-Electrochemical CO Reduction on Multi-Junction Photoabsorbers

Substantial research effort has been dedicated to the electrochemical reduction of CO2 (CO2R) to higher carbon products throughout the recent years, baring the promise of a production pathway for green fuels and chemicals.1 However, only little progress has been achieved in the light driven heterogeneous CO2R catalysis, especially considering selective processes towards C2+ products. This arises from the additional complexity of photo-electrochemical reactions, which means that not only the sluggish reaction kinetics, high overpotentials and low selectivity of CO2R, but also the insufficient voltage and sensitivity towards harsh electrolyte conditions of photoabsorbers have to be encountered. Considering CO2R as multi-step process with CO as intermediate mitigates some issues of the process, e.g. the necessary overpotential is reduced and a higher selectivity towards valuable products can be achieved.2 Multi-junction solar stacks can provide operating voltages >2 V, which is sufficient for reducing CO2 to CO with high efficiencies or even produce multi-carbon products from CO while oxidizing water as anode reaction.3 In this work, we designed a process for photo-electrochemical CO reduction with multi-junction photoabsorbers. We start out by showing photo-electrochemical modelling of tandem photoabsorbers that emphasizes the advantages of CO as reactant compared to CO2. Further, we focus on the preparation of a nano-structured Cu catalyst, the most common material for reducing CO to C2+. Therefore, the electrochemical deposition and surface characterization using SEM, EDX and XPS of the catalyst on a dark model electrode coated with a sputter deposited TiO2 protection layer will be presented. Moreover, the CO reduction performance of the model at different potentials are characterized. In addition, the light transmission of the model electrode is reported, baring the possibility of illuminating the photoelectrode from the catalyst front side in mind. Lastly, the transfer of the model catalyst to a photoabsorber as well as the design of a photo-electrochemical flow-cell are discussed. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Rev. 119, 7610–7672 (2019)1.Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catal. 8, 7445–7454 (2018)Seger, B., Hansen, O. & Vesborg, P. C. K. A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. RRL 1, e201600013 (2017). Figure 1

Dual Functional High Donor Electrolytes for Lithium–Sulfur Batteries under Lithium Nitrate Free and Lean Electrolyte Conditions

Dual Functional High Donor Electrolytes for Lithium–Sulfur Batteries under Lithium Nitrate Free and Lean Electrolyte Conditions

Electrochemical Detection and Analysis of Various Current Responses of a Single Ag Nanoparticle Collision in an Alkaline Electrolyte Solution.

A single silver (Ag) nanoparticle (NP) collision was observed and analyzed in an alkaline solution using the electrocatalytic amplification (EA) method. Previously, the observation of a single Ag NP collision was only possible through limited methods based on a self-oxidation of Ag NPs or a blocking strategy. However, it is difficult to characterize the electrocatalytic activity of Ag NPs at a single NP level using a method based on the self-oxidation of Ag NPs. When using a blocking strategy, size analysis is difficult owing to the edge effect in the current signal. The fast oxidative dissolution of Ag NPs has been a problem for observing the staircase response of a single Ag NP collision signal using the EA method. In alkaline electrolyte conditions, Ag oxides are stable, and the oxidative dissolution of Ag NPs is sluggish. Therefore, in this study, the enhanced magnitude and frequency of the current response for single Ag NP collisions were obtained using the EA method in an alkaline electrolyte solution. The peak height and frequency of single Ag NP collisions were analyzed and compared with the theoretical estimation.

Cobalt-embedded 3D conductive honeycomb architecture to enable high-sulphur-loading Li-S batteries under lean electrolyte conditions

Cobalt-embedded 3D conductive honeycomb architecture to enable high-sulphur-loading Li-S batteries under lean electrolyte conditions

Effectively engineering in situ coupled cobalt-cobalt phosphide nanoparticles with nitrogen-doped carbon materials for advanced bifunctional oxygen electrocatalysts in rechargeable Zn-air batteries

Constructing efficient and inexpensive bifunctional catalysts with oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) is urgently requisite for advanced Zn-air batteries. Herein, a composite material consisting of cobalt-cobalt phosphide nanoparticles in situ coupled with N-doped carbon (Co-Co2P @ NC) is conveniently engineered via a facile all-in-one carbonization/phosphorization process. Specifically, Co-Co2P @ NC implements unprecedented bifunctional catalytic activities with a positive ORR half-wave potential of 0.858 V and a low OER potential of 1.598 V at 10 mA cm−2, outperforming the benchmark catalysts and is on a par with recently reported non-precious metal-based catalysts. These impressive electrocatalytic performances are attributable to the synergistic coupling effects between metallic Co, Co2P and NC, extraordinary specific surface area, rich active species and conductive carbon frameworks. Prominently, a rechargeable aqueous ZAB with Co-Co2P @ NC as an air cathode catalyst delivers an ultra-long term cycling stability of more than 2000 h (over continuous 6000 cycles) with a small change of charge-discharge voltage gap from 0.841 V to 0.890 V at 2 mA cm−2. Beyond that, both button-like and foldable quasi-solid-state ZABs also exhibit admirable performance even under the limited electrolyte condition, evidently indicating the wide adaptability and feasibility in practical energy conversion and storage.

Electrochemical discharge machining of microchannels in glass using a non-Newtonian fluid electrolyte

The gas film plays a key role in electrochemical discharge machining (ECDM). However, the impact force of the electrochemical discharge affects the gas film and hence can lower the machining performance. To improve the stability of the gas film, a novel ECDM approach based on a non-Newtonian fluid electrolyte, i.e. the mixture of Polyacrylamide and KOH is proposed in this study. The experimental results show that, compared to the traditional Newtonian fluid KOH electrolyte, the non-Newtonian fluid electrolyte can significantly weaken the effect of the impact force on the gas film, and thus the gas film was more stable. The theoretical model and experimental results both show that stable electrochemical discharge and a lower critical voltage can be achieved with a non-Newtonian fluid electrolyte condition for its’ gas film is thinner and more stable than with the KOH electrolyte. With the non-Newtonian fluid electrolyte, the heat-affected zone and entrance overcut of the microchannels were both smaller than with the KOH electrolyte. In this study, a complex microchannel with a depth of 100 µm and a spacing of 30 µm was successfully fabricated. This is the smallest spacing reported so far in the literature for a microchannel fabricated in glass using ECDM. Moreover, a smoother machining surface with Ra 0.45 µm was obtained with the non-Newtonian fluid electrolyte. It can be concluded that using the non-Newtonian fluid electrolyte is a simple and effective way to enhance the stability of gas film and thus, improve the micromachining performance of ECDM.

Phosphorus-doping promotes the electrochemical etching of metals to nanoporous electrodes for efficient and durable overall water splitting

Electrocatalysts play a central role in electrochemical water splitting to store renewable energy in the chemical fuel of hydrogen. Nanoporous metal electrodes are promising to boost hydrogen production efficiency while challenging in synthesis. Here, a phosphorus-doping assisted electrochemical etching strategy is developed to construct highly nanoporous surfaces on metal electrodes, leading to a remarkable catalytic performance for overall water splitting under lab-level or industrial electrolysis conditions. Specifically, the nanoporous FeCoNiCu foil shows 46 times higher electrochemical surface area, lowering the overpotentials by 102 mV for oxygen evolution reaction and 157 mV for hydrogen evolution reaction. The viability of the strategy is further demonstrated in the prevailing industrial electrodes of nickel meshes, enabling a cell voltage of only 1.931 V under the harsh industrial electrolytic condition (80 °C, 30 wt% KOH, and a current density of 500 mA cm−2). It is 126 mV lower than that of a bare nickel mesh-based electrolyzer and corresponds to a ∼4% improvement in energy-conversion efficiency. This work offers a facile and ease-to-scale-up approach for the upgrading of widespread metal electrodes, possessing great prospects in energy conversion and storage devices including electrolyzers, fuel cells, batteries, and supercapacitors.

Synergism of Flame‐Retardant, Self‐Healing, High‐Conductive and Polar to a Multi‐Functional Binder for Lithium–Sulfur Batteries

AbstractIn this work, a multifunctional binder with self‐healing, flame retardant, high conductivity, and abundant polar groups is prepared by the free radical polymerization method and applied to lithium–sulfur (Li‐S) batteries to achieve high safety and exceptional electrochemical performance. The self‐healing characteristic of binder induced by intermolecular hydrogen bonds and SS dynamic covalent bonds can repair volume expansion cracks. The polar groups and excellent conductivity endue binder with strong chemisorption on polysulfides and fast charge transportation, which can effectively inhibit the shuttle effect and accelerate polysulfides redox kinetics. More important, the considerable flame retardant performance of binder can improve the safety of the LiS batteries. As a result, the LiS cells using FHCP binder deliver an outstanding cycle stability of a high‐capacity retention rate of 85% after 100 cycles at 0.2 C, and a high reversible area specific capacity of 5.25 mAh cm–2 at a sulfur loading of 4.72 mg cm–2 and a correspondingly lean electrolyte condition (E/S ratio = 6 µL mg–1).

Mechanical–electrochemical coupling theory of bacterial cells

The environmental adaption, growth, motion, and other dynamic behaviors of bacteria are closely associated with the coupled mechanical–electrochemical properties of their subcellular structures, but the underlying regulatory mechanisms remain unclear. The mechanical responses of bacteria are difficult to elucidate by traditional models without considering the mechanical, chemical, and electric coupling effects. In this paper, a mechanical–electrochemical theory is constructed to investigate the deformation behavior of bacterial cells. A bacterium is treated as a bilayer structure consisting of a negatively charged polysaccharide capsule and an elastic envelope subjected to turgor pressure. This model is used to reveal the regulating roles of the electrostatic double-layer force and osmosis under different electrolyte conditions. Good agreement is found between the theoretical predictions and the experimentally observed three-stage nanoindentation responses of Klebsiella pneumoniae (K. pneumoniae) bacterial cells. Furthermore, we investigate the mechanical–electrochemical coupling mechanisms in the compression resistance of the bacterial capsule. The results reveal that the osmosis induced by ionic imbalance and polysaccharide–solvent aggregates plays a significant role in the compression resistance of the capsule. The present model not only deepens our understanding of the mechanical–electrochemical coupling mechanisms of bacterial cells at the subcellular scale, but also holds promise for applications in characterizing their mechanical properties.

High-performance prelithiated Si-S full cell enabled by trifluorobenzene modified diluted high-concentration electrolyte

Silicon-sulfur (Si-S) full cells show significant potential in energy storage due to their high theoretical energy density compared to commercial lithium-ion batteries. Nevertheless, a majority of electrolytes reported for Si-S full cells still cannot meet the requirements of stable long-duration cycling. Herein, we report a high-areal-capacity Si-S full cell consisted with prelithiated SiO, thick Li2S-Se0.05S0.95@pPAN electrode and a trifluorobenzene (F3B) modified and diluted high-concentration electrolytes. This novel electrolyte can effectively mitigate the volume expansion of the prelithiated SiO anode and enhance the utilization of active S in the cathode, showing excellent compatibility with electrodes. The assembled Si-S full cell using modified electrolyte displays remarkable cyclability over 100 cycles at 0.1C, exhibiting higher capacity retention (54.0% vs. 17.5%) than the pristine electrolyte without F3B. More importantly, a full cell with a thick sulfur cathode (16 mg/cm2) exhibits a superior initial areal capacity of 8.34 mAh/cm2 and high-capacity retention of 52% after 80 cycles, even at a lean electrolyte condition (2 μL/mg). This work provides guidance for the achievement of high-performance Si-S full cells under lean electrolytes.

Phase-transition tailored nanoporous zinc metal electrodes for rechargeable alkaline zinc-nickel oxide hydroxide and zinc-air batteries

Secondary alkaline Zn batteries are cost-effective, safe, and energy-dense devices, but they are limited in rechargeability. Their short cycle life is caused by the transition between metallic Zn and ZnO, whose differences in electronic conductivity, chemical reactivity, and morphology undermine uniform electrochemical reactions and electrode structural stability. To circumvent these issues, here we propose an electrode design with bi-continuous metallic zinc nanoporous structures capable of stabilizing the electrochemical transition between metallic Zn and ZnO. In particular, via in situ optical microscopy and electrochemical impedance measurements, we demonstrate the kinetics-controlled structural evolution of Zn and ZnO. We also tested the electrochemical energy storage performance of the nanoporous zinc electrodes in alkaline zinc-nickel oxide hydroxide (NiOOH) and zinc-air (using Pt/C/IrO2-based air-electrodes) coin cell configurations. The Zn | |NiOOH cell delivers an areal capacity of 30 mAh/cm2 at 60% depth of discharging for 160 cycles, and the Zn | |Pt/C/IrO2 air cell demonstrates 80-hour stable operation in lean electrolyte condition.

Ion-regulating Hybrid Electrolyte Interface for Long-life and Low N/P Ratio Lithium Metal Batteries

Practical lithium metal batteries (LMBs) require full and reversible utilization of limited metallic Li anodes at a solid/quasi-solid electrolyte condition. This leads to a challenging issue, i.e., how to create compatible interphases to regulate interfacial ionic transport and protect the reactive metal. Herein, to address this issue, we report a robust cellulose-based composite gel electrolyte (r-CCE) capable of stabilizing ion deposition via compositing bacterial cellulose (BC) skeleton with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles. Benefiting from the decoupled segment structure of cellulose and additional ionic channels of LLZTO, r-CCE not only achieves high ionic conductivity (1.68 × 10−3 S/cm) with a remarkable Li-ion transfer number (∼0.92) and a wide window of electrochemical stability (∼5.3 V), but also helps stabilize the Li anode. Utilizing ultrathin lithium metal anodes (15 μm), ultra-stable symmetric Li/Li cells that are armed with r-CCE demonstrate a highly stable plating/stripping process. Furthermore, a high areal capacity of ∼4.2 mAh/cm2, and 100 cycles with improved stability of the full Li metal batteries with n/p ratio of ∼0.74 are achieved.

Development of Core-Shell Rh@Pt and Rh@Ir Nanoparticle Thin Film Using Atomic Layer Deposition for HER Electrocatalysis Applications

The efficiency of hydrogen gas generation via electrochemical water splitting has been mostly limited by the availability of electrocatalyst materials that require lower overpotentials during the redox reaction. Noble metals have been used extensively as electrocatalysts due to their high activity and low overpotentials. However, the use of single noble metal electrocatalyst is limited due to atomic aggregation caused by its inherent high surface energy, which results in poor structural stability, and, hence, poor electrocatalytic performance and long-term stability. In addition, using noble metals as electrocatalysts also causes the cost to be unnecessarily high. These limitations in noble metal electrocatalysts could be enhanced by combining two noble metals in a core-shell structure (e.g., Rh@Ir) as a thin film over a base substrate. This could significantly enhance electrocatalytic activity due to the following: (1) the modification of the electronic structure, which increases electrical conductivity; (2) the optimization of the adsorption energy; and (3) the introduction of new active sites in the core-shell noble metal structure. The current state-of-the-art employs physical vapor deposition (PVD) or other deposition techniques to fabricate core-shell noble metals on flat 2D substrates. This method does not allow 3D substrates with high surface areas to be used. In the present work, atomic layer deposition (ALD) was used to fabricate nanoparticle thin films of Rh@Ir and Rh@Pt in a core-shell structure on glassy carbon electrodes. ALD enables the fabrication of nanoparticle thin film on three-dimensional substrates (a 2D functional film on a 3D substrate), resulting in a significantly increased surface area for a catalytic reaction to take place; hence, improving the performance of electrocatalysis. The Rh@Pt (with an overpotential of 139 mV and a Tafel slope of 84.8 mV/dec) and Rh@Ir (with an overpotential of 169 mV and a Tafel slope of 112 mV/dec) core-shell electrocatalyst exhibited a better electrocatalytic performances compared to the single metal Rh electrocatalyst (with an overpotential of 300 mV and a Tafel slope of 190 mV/dec). These represented a 54% and a 44% improvement in performance, respectively, illustrating the advantages of core-shell thin film nanostructures in enhancing the catalytic performance of an electrocatalyst. Both electrocatalysts also exhibited good long-term stability in the harsh acidic electrolyte conditions when subjected to chronopotentiometry studies.

Syngas mediated microbial electrosynthesis for CO2 to acetate conversion using Clostridium ljungdahlii

Carbon dioxide valorization through microbial electrosynthesis (MES) is promising due to it's potential for mild operating conditions and stable long-term performance. Previous MES studies have typically shown poor organic production rates using direct electron transfer mechanisms, prompting the use of electrochemically generated H2 to provide reducing equivalents for improved carbon utilization via metabolisms like the Wood-Ljungdahal pathway. Still, CO is a more favorable electron donor than H2 as it provides more thermodynamic reducing power for conversion of CO2 into valuable products. Here, we incorporated highly selective cobalt phthalocyanine catalysts into new planar 2D and porous 3D MES cathodes to produce syngas rather than H2 and boost the overall bioconversion rates of CO2 into value-added products (i.e. acetate and ethanol). Both the 2D and 3D systems were able to consistently generate syngas for over 250 h using microbial media electrolyte, demonstrating excellent stability in challenging electrolyte conditions. However, the 2D planar cathodes required a larger potential to maintain similar current densities as the 3D porous cathodes (-1.8 V vs. -1.2 V vs. Ag/AgCl) and showed a slow decline in CO production (0.23 ml/min–0.09 ml/min) and increase in H2 (0.01 ml/min–0.13 ml/min) production after 250 h. In comparison, the 3D porous electrodes allowed for more stable CO (0.08–0.06 ml/min) and H2 (0.16–0.06 ml/min) generation that also led to higher maximum acetate (5.1 vs. 3.8 g/L) and ethanol (1.2 vs. 0.9 g/L) titers. Demonstration of these new cathode materials shows significant progress towards more stable and effective MES operations and delivers useful insight on syngas mediated electron transfer and utilization in bioelectrochemical systems.

Optimization of the membrane electrode assembly for an alkaline water electrolyser based on the catalyst-coated membrane

This study deals with the preparation and characterisation of catalyst-coated membranes for an alkaline water electrolysis process. For this purpose, a chloromethylated anion-selective block copolymer of styrene-ethylene-butylene-styrene with 1,4-diazabicyclo[2.2.2]octane functional groups was used both as an alkaline polymer electrolyte membrane and as an ionomer binder. Non-PGM catalysts (platinum group metals), specifically NiCo2O4 and NiFe2O4, were used on the anode and cathode side of the membrane, respectively. Air-brush deposition or computer-controlled ultrasonic dispersion of the catalytic ink were used to deposit the catalyst layers. The influence of the composition of the catalyst layer on its stability and the resulting electrolysis cell performance was investigated under typical membrane alkaline water electrolysis conditions (1–15 wt.% KOH, 45 °C). The optimal catalyst-to-binder ratio in the catalyst layer was identified as 93/7 using a catalyst loading of 2.5 mg cm-2 on each side of the membrane. The membrane electrode assembly prepared under optimal conditions showed high stability over 140 h at a current density of 250 mA cm-2. At this current load, the cell exhibited a voltage of 2.025 ± 0.010 V. The increase in cell voltage observed during the stability test did not exceed 1 μV h-1.

Caustic aqueous phase electrochemical reforming (CAPER) of ethanol for process intensified compressed hydrogen production

The Caustic Aqueous Phase Electrochemical Reforming (CAPER) process can convert aqueous-phase ethanol to high-pressure and high-purity hydrogen (H2) at lower cell operating temperatures and voltages than traditional methods. Additionally, any carbon dioxide (CO2) produced by the ethanol electrochemical oxidation is captured by the caustic electrolyte solution. Without using a membrane, the only gas-phase species is H2. The CAPER process achieves process intensification for compressed and pure H2 production by eliminating the need for downstream separation and external compression steps. All the compression is performed on the liquid-phase reactants to circumvent less efficient gas-phase compression. This study uses a high-pressure batch electrochemical reactor to demonstrate the capability of the CAPER reforming process and investigates catalytic behavior under operating conditions. Our Tafel analysis showed that both palladium and platinum nanoparticles on carbon supports have high activity for ethanol electrooxidation under the caustic electrolyte condition (exchange current density (i0) > 1 × 10−5 A cm−2), while non-noble nanoparticles on carbon supports showed poor activity. The only gas phase product was pressurized H2 and its faraday efficiency was determined as 100%. The exchange current density was not affected by high-pressure operation. The carbon selectivity toward unwanted byproduct acetate on the anode increased from 17% to 63% as the applied anode potential increased from −500 mV to −200 mV vs. Ag/AgCl.

Early Failure of Lithium-Sulfur Batteries at Practical Conditions: Crosstalk between Sulfur Cathode and Lithium Anode.

Lithium–sulfur (Li–S) batteries are one of the most promising next‐generation energy storage technologies due to their high theoretical energy and low cost. However, Li–S cells with practically high energy still suffer from a very limited cycle life with reasons which remain unclear. Here, through cell study under practical conditions, it is proved that an internal short circuit (ISC) is a root cause of early cell failure and is ascribed to the crosstalk between the S cathode and Li anode. The cathode topography affects S reactions through influencing the local resistance and electrolyte distribution, particularly under lean electrolyte conditions. The inhomogeneous reactions of S cathodes are easily mirrored by the Li anodes, resulting in exaggerated localized Li plating/stripping, Li filament formation, and eventually cell ISC. Manipulating cathode topography is proven effective to extend the cell cycle life under practical conditions. The findings of this work shed new light on the electrode design for extending cycle life of high‐energy Li–S cells, which are also applicable for other rechargeable Li or metal batteries.