Electrodes For Oxygen Evolution Reaction Research Articles

MOF nanosheet array-derived NiS with Co, N-doped carbon layer: A highly efficient oxygen evolution electrocatalyst

The development of the hydrogen industry from electrolytic water is confined in great measure to the slow kinetics of oxygen evolution reaction (OER), which means the rational design of a stabilized and efficient OER electrode is the key. The construction of easily accessible hydroxide ion (OH−) adsorption sites can effectively accelerate the kinetics of the OER. Herein, the NiS/CoNC electrocatalysts, which can effectively adsorb OH− and exhibited excellent OER performance in an alkaline environment, were obtained by pyrolysis and sulfidation of NiCo-MOF nanosheets on nickel foam (NF). In particular, the optimized NiS/CoNC electrocatalyst achieved an overpotential of 46/106 mV at 10/100 mA cm−2 and Tafel slope of 57.41 mV dec−1, which is superior to most reported materials. The outstanding function of OER results from the NiOOH/CoOOH active component generated by surface reconstruction after activation of the NiS/CoNC catalyst and the excellent charge transfer capability of the NiS component. This work offers a scheme to construct the electrocatalysts derived from MOF with excellent OER performance.

Wet Gas Water Feed of Polymer Electrolyte Membrane Electrolyzer for Simultaneous Hydrogenation of Organic Chemical Hydride Energy Carrier and Water Decomposition

To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition using proton exchange membrane (PEM) electrolysis. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation.As shown in Figure 1, anode reaction produces oxygen and proton, and proton transports cathode electrocatalyst layer through the PEM with water molecular. Water inhibits toluene transportation to reaction side and hydrogen evolution occurs as side reaction. We have reported electrolyzers that has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction, and sulfuric acid solution feeds as anolyte that is not only reactant but also for water management. Water back diffusion from cathode to anode enhances with sulfuric acid concentration. In addition, current efficiency with mesh type anode was higher than that with sintered fiber sheet type anode. The mesh shape of electrode makes current distribution that affects mass transfer pass distribution to improve current efficiency, although sheet type anode is lower overpotential because of large surface area [1 – 3]. As practical system, water transportation from anode to cathode should be supressed without sulfuric acid utilization, and electrochemical surface- area of anode should extend to reduce overpotential.In this study, we have investigated wet gas water feed for PEM electrolysis to reduce water transfer to cathode, because water transfer would control by relative humidity of wet gas that feed to anode for oxygen evolution reaction. Here, PEM water electrolysis type anode catalyst layer with ionomer was employed to reduce anode overpotential and to maintain ionic conduction in catalyst layer.Figure 1 shows the schematic drawing of toluene direct hydrogenation electrolyzers with water splitting. Figure 1 (a) is our conventional electrolyzer of H2SO4 solution feed, and Figure 1 (b) is wet air feed in this study. The anode side for wet air feed had polymer electrolyte fuel cell type serpentine gas flow channel. Anode catalyst layer was 1.0 mg cm-2 of IrOx (TKK) with Nafion ionomer. The porous transport layer was platinum plated sintered titanium sheet. PEM was Nafion 117 (Du Point), cathode catalyst layer was 0.5 mg cm-2 of PtRu/C with Nafion ionomer supported on a porous flow field of a carbon paper that was loaded 0.02 mg cm-2 platinum for chemical reaction of toluene and hydrogen.5 mL min-1 of toluene or 10% toluene – methylcyclohexane and 1.0 L min-1 of wet air fed to cathode and anode, respectively. Operation temperature was 80oC. After the 100 % RH feed electrolysis, there is no product except methylcyclohexane in the liquid phase and water transportation from anode to cathode reduced one twentieth from the conventional electrolyzer fed 1 M H2SO4 operation at 60oC. In this condition, IR free cell voltage of the wet gas fed electrolyzer was significantly smaller than that of the conventional one because of high surface area anode. Internal resistance of the wet gas feed determined by AC impedance method was about two times higher than that of the conventional, and current efficiency maintained in the low current density region. The internal resistance increased in the high current density region where the membrane and ionomer dry up with electro osmosis water. In this region, current efficiency also decreases.In summary, wet gas feed water electrolysis for electrohydrogenation of toluene using a PEM electrolyzer is an interesting technology that combines water electrolyzer with water purification system and manages water feed to reduce water transportation to cathode to maintain current efficiency of with accurate control of relative humidity and gas feed amount.AcknowledgementThis study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).References Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitsushima, J Power Sources, 439, 227070 (2019).Oi, K. Nagasawa, T. Takamura, Y. Misu, K. Matsuoka, S. Mitsushima, ECS Meeting s, MA2021-02, 1737 (2021).Mitsushima, Y. Sugita, J. Koike, Y. Kuroda, K. Matsuoka, Y. Sato, K. Nagasawa, ECS Meeting s, MA2020-02, 2494 (2020). Figure 1

Understanding Performance and Durability with KOH and DI-Water Fed Anion Exchange Membrane Electrolyzers

Anion Exchange Membrane electrolyzers (AEMELs) have increased in popularity in recent years due to their potential to combine the benefits from proton exchange membrane electrolyzers and traditional alkaline electrolyzers – namely, high current density operation, pressurized H2 discharge and lowering cost by utilizing low-cost earth abundant electrocatalysts and inexpensive component materials. In the AEMEL, the oxygen evolution reaction (OER) electrode plays a critical role dictating the overall efficiency of the cell due to sluggish OER activity and species transport. In our previous study, we optimized the OER electrode structure by investigating the effects of catalyst loading, catalyst type, the porous transport substrate and additive carbon [1] – resulting in an excellent performance of 1.55 V operation at 1.0 A/cm2.Though that study led to high performance, all of those gains were made using KOH electrolyte being fed to the cell, not deionized (DI) water. The use of DI water complicates AEMEL operation as the liquid phase can no longer be relied on to carry any of the ionic charge – this possibly can reduce the electrochemically active surface area (ECSA) [2]. It has also been stated that pure water operation may have negative consequences on cell durability. Therefore, to allow for AEMELs to operate efficiently on DI water, it is important to understand how the ion transport and charge transfer resistance change as cells are transitioned from KOH to DI water operation. It is also important to understand what effects even trace amounts of KOH can have on behavior. Lastly, the effect of the ionomer properties on the OER anode performance should be well-understood.In this study, we investigate the role of alkaline feed pH on the performance and durability of AEMELs. When shifting from alkaline feed to DI water, it will be shown that there is an increase in ohmic and charge transfer resistance, resulting in significant voltage loss. Because the alkaline feed enhances electrode conductivity by connecting catalyst active sites to the conductive ionomer and AEM [2-3], new electrode structures are needed that allow for enhanced ECSA and lower resistances with DI water feeds. In this work, that was accomplished by creating a four-layer electrode structure as well as manipulating the cell operating conditions. Lastly, our team enabled the use of a high IEC ionomer in the anode catalyst layer by introducing a cross-linker and introducing smaller, cryo-milled ionomer particles. This was important to overcome adhesion issues that can come from high water uptake and swelling in high-IEC ionomers [4-5]. This paper will focus not only on performance, but also longevity, with several cells being stably operated for more than 500 hours continuously.

Role of Ionomer Dispersion in the Design of Microstructure of Catalyst Layers: Oxygen and Hydrogen Evolution Reactions

Green hydrogen production is importance in the upcoming hydrogen economy era. Proton exchange membrane (PEM) water electrolysis is one of the most important technology to produce the green hydrogen that requires only water and extra electricity supplied from renewable energy. Main component, i.e., membrane electrode assembly (MEA), is a key part consisting of polymer electrolyte membrane and two electrodes which are oxygen evolution reaction (OER) electrode and hydrogen evolution (HER) electrode. Both electrode should be coated on the surface of membranes for better performance and mass production. Catalyst layers for OER and HER electrodes are composed of an electrocatalyst (Pt/C) and proton conducting ionomer. In the previous literature, proton conducting ionomer directly affects their performance and durability. Thus, the optimized design of the microstructure of the catalyst layers is essential. In this study, for the reduction of hydrogen production cost, highly dispersed ionomers were introduced to develop the optimized catalyst layers for OER and HER. The effect of dispersing solvents for ionomers on the performance and durability of catalyst layers was mainly investigated. Developed ionomer dispersions showed higher performance and durability in PEM water electrolysis, which result was made by the electrochemical characterization such as I-V polarization, voltage increasing rate during durability test, and so on as well as the microscopic characterization such as SEM and TEM were carried out to evaluate the effect of ionomer dispersions on the performance and durability of HER electrode in PEM water electrolysis. Acknowledgments This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT ＆ Future Planning (NRF-2019M3E6A1063677) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Metal-Coordinated Hydrogels As Efficient Oxygen Evolution Electrocatalysts

Conductive polymer hydrogels have large surface area and high conductivity. Their properties can easily be tailored further by functionalizing them with metals and nonmetals. However, the potential of metal-conjugated hydrogels for electrocatalysis has rarely been investigated. In this work, we report the synthesis of transition metals-conjugated polyaniline-phytic acid (PANI-PA) hydrogels that show efficient electrocatalytic properties for the oxygen evolution reaction (OER). Among many transition metals studied, Fe is accommodated by the hydrogel the most because of the favorable affinity of the PA groups in the hydrogel for Fe. Meanwhile, those containing both Fe and Co are found to be the most effective for electrocatalysis of OER. The most optimized such hydrogel, NF@Hgel-Fe0.3Co0.1, which has 3:1 ratio of Fe and Co, needs an overpotential of only 280 mV to catalyze OER with a current density of 10 mV cm-2 in 1 M KOH solution. Furthermore, these metal-doped PANI-PA hydrogels can easily be loaded on nickel foam and carbon cloth via a simple soak-and-dry method to form free-standing electrodes. Overall, the work demonstrates a facile synthesis and fabrication of sustainable OER electrocatalysts and electrodes that are composed of easily processable hydrogels conjugated with various earth-abundant transition metals.Figure R. Schematic illustration of the synthesis of PA-PANI-Metal (Hgel-M x ) hydrogels for electrocatalysis of OER. Figure 1

Gas-Liquid Interfacial Plasma engineering under dilute nitric acid to improve hydrophilicity and OER performance of nickel foam

The world has been moving rapidly to find new eco-friendly energy sources. Water electrolysis consists of two reactions of Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER), whereas the OER is considered the rate-limiting step. The most commercialized electrode for OER in the alkaline electrolyte is Ni foam, but its original surface is hydrophobic. It is possible to accelerate the adsorption and desorption process of reactants and products during OER by adding hydrophilic functional groups such as –OH on the surface of Ni foam. In this study, a novel Gas-Liquid Interfacial Plasma (GLIP) engineering at room temperature was successfully applied to modify the Ni foam surface dilute (1 ​M) HNO3 solution. At a current density of 400 ​mA ​cm−2, GLIP-treated Ni foam electrodes at 1 ​M HNO3 concentrations showed OER overpotentials of 458 ​mV. Among all, GLIP with 1 ​M HNO3 treatment of 30 ​min showed 129 ​mV less overpotential than the nickel foam before treatment. In summary, GLIP can be justified as an environmentally friendly and efficient surface treatment to improve the wettability and OER performance of Ni-based electrodes in water electrolysis.

Fe doped NiSe2 nanoarrays to boost electrocatalytic oxygen evolution reaction

• Fe doped NiSe 2 on carbon cloth (CC) catalysts were synthesized by a two-step hydrothermal method. • Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . • Doping engineering strategy makes Ni 0.8 Fe 0.2 Se 2 /CC manifest a superb performance for OER. • Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which serves as “real” active phase. Transition metal selenides (TMSes) have attracted increasing attention for electrocatalysts due to fascinating properties, such as low cost, intrinsic metallic properties, and high catalytic activities. In addition, bimetallic selenides exhibit more excellent performance in the oxygen evolution reaction (OER) process than monometallic selenides via synergistic effect. Herein, we synthesized Fe doped NiSe 2 on carbon cloth (CC) employed as electrodes for boosting OER by a facile two-step hydrothermal method. These electrodes display excellent electrocatalytic activity for OER in alkaline electrolytes, in which Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . The synthesized three-dimensional structure with the aid of carbon cloth helps for the mass and charge transfer. Furthermore, Fe doping not only induces stronger electron interaction but tunes electronic structure, thus improving the OER performance. After a long-term OER process, Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which may serve as “real” active phase. Doping engineering strategy makes TMSes manifest a superb performance for OER and expands ways for designing effective OER electrodes. Herein, we synthesized Fe doped NiSe 2 on carbon cloth (CC) employed as electrodes for boosting OER by a facile two-step hydrothermal method. These electrodes display excellent electrocatalytic activity for OER in alkaline electrolytes, in which Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . Fe doping not only induces stronger electron interaction but enlarges Ni 3+ /Ni 2+ ratio, thus improving the OER performance. Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which serve as “real” active phase in OER process.

Ferric ions leached from Fe-based catalyst to trigger the dynamic surface reconstruction of nickel foam for high-efficient OER activity

The understanding of the interactions between catalyst and support is very important in heterogeneous catalysis of water splitting; however, it is still lacking. Herein, a Fe-based material of rod-like Fe2OF4 is fabricated as the oxygen evolution reaction (OER) electrocatalyst. Strikingly, Fe2OF4 loaded on nickel foam support can exhibit high-efficient OER activity with low overpotential and Tafel slope. Furthermore, we reveal that partial ferric ions within Fe2OF4 can leach out into electrolyte; and then the ferric ions are electrochemically adsorbed on the surface of nickel foam, triggering dynamic surface reconstruction to generate highly active FeNi-oxyhydroxides under alkaline OER condition. Further, based on our findings, a promising approach is successfully proposed to prepare a large-size, low-cost and high-performance OER electrode via surface reconstruction on NF with ferric ions, showing remarkable performance. This work provides new insights into catalyst-support interactions, and proposes a straightforward surface reconstruction strategy for the scaling-up of electrocatalysts.

Binary Layered Double Hydroxide Electrode Array Synthesized via Metal Alloy Corrosion for Oxygen Evolution Reaction

Developing highly efficient and cost-effective anodic electrodes is one of the major challenges in hydrogen evolution via water electrolysis technology. We demonstrate that the chloride corrosion can transform commercial Ni–Fe alloy (invar) into an electrode, revealing a high-efficiency oxygen evolution reaction (OER). The corroded electrode consisted of a dense vertical array of NiFe layered double hydroxide (LDH) nanosheets on the invar foil surface. We discovered that the corrosion rate difference between metallic components of the binary metal serves the growth of the NiFe LDH at the invar surface. This NiFe LDH electrode required an overpotential of 211 mV at a current density of 10 mA/cm2 in 1 M KOH, outperforming the commercial IrO2 catalyst by 47 mV. This electrode showed excellent activity against OER owing to their high intrinsic electrical conductivity of direct growth and high electrochemical surface area of NiFe LDH nanosheets. Furthermore, this electrode exhibited excellent electrochemical stability without decay in performance for 7 days at the current density of 50 mA/cm2. This study provides rationally designed electrocatalysts with high and stable catalytic activity to obtain a convenient route to the large-scale production of OER electrodes.

Metal–organic framework derived CoS2/FeS-MOF with abundant heterogeneous interface as bifunctional electrocatalyst for electrolysis of water

Highly active and stable non-precious metal dual-functional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are very important for the industrialization of water electrolysis. Herein, a three-dimensional (3D) porous CoS2/FeS-MOF with adjustable Co/Fe molar ratio are in-stiu grown on a nickel foam (NF) to get a binder-free electrocatalyst electrode for HER and OER (CoS2/FeS-MOF@NF). It should be emphasized that the MOFs precursor forms abundant heterogeneous interfaces through in-situ sulfidation. Moreover, the open skeleton and ordered porous structure of MOFs will not be destroyed due to the low temperature. The redistribution of electrons at the heterogeneous interfaces will produce more catalytic active centers, providing more active sites for reactant molecules or intermediates, thus availably promoting the electrocatalytic activity of the composite. Therefore, the optimized catalyst CoS2/FeS-MOF@NF-1 displays high OER activity. The overpotential is only 136 mV at 10 mA cm−2. At the same time, the CoS2/FeS-MOF@NF-1 also shows good HER catalytic activity. Therefore, the assembled corresponding symmetric electrolyzer CoS2/FeS-MOF@NF-1||CoS2/FeS-MOF@NF-1 achieves a low cell voltage of 1.5 V at 10 mA cm−2 with long time stability for 24 h. This work provides a simple and convenient strategy for the synthesis of transition metal sulfides dual-function electrocatalysts.

MoS 2 nanosheets as bifunctional electrode for oxygen evolution reaction and electrochemical supercapacitor

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Compositional modulation by elemental leaching and chronoamperometric aging of 4J36 INVAR alloy for facile and efficient oxygen evolution reaction

A commercially available INVAR alloy was subjected to the electrochemical conditionings including Fe-leaching and chronopotentiometric aging, to modulate surface composition and stabilize electrocatalysts for efficient and facile oxygen evolution reaction (OER). Owing to the complexing function of KSCN during Fe-leaching for the optimum Ni/Fe ratio and the stabilization of Fe-doped (oxy)hydroxides under the adequately higher current density within alkaline media, the OER electrode composed solely of 4J36 INVAR alloy as substrate needs an overpotential of only 250 mV to attain 10 mA cm −2 in 1 M KOH, besides its performance stability at two different current densities. This simple and cost-effective fabrication of OER electrode, which is binder-free, self-supporting and matrix-rejuvenating, will open a new door to the cutting-edge design of electrocatalyst for water splitting.

In-situ etching of stainless steel: NiFe2O4 octahedral nanoparticles for efficient electrocatalytic oxygen evolution reaction

The development of non-noble metal electrocatalysts for oxygen evolution reaction (OER) has attracted widespread attention in the field of energy. Herein, we report a facile in-situ etching method to convert commercial stainless steel felt (SSF) into NiFe 2 O 4 octahedral nanoparticles as an efficient and robust OER electrode. This preparation method of NiFe 2 O 4 is different from the conventional ones, both nickel and iron elements come from the substrate itself without extra addition of precursors, as well as NiFe 2 O 4 octahedral nanoparticles are self-grown directly on the substrate without binder. The treated SSF shows good water oxidation properties with low overpotential, small Tafel slope, and durable stability at 500 mA cm −2 for 200 h. Moreover, the effect of NaNO 3 in the etchant is studied carefully, which plays the function of removal of chromium and promoting the formation of octahedral nanoparticles, resulting in the enhancement of conductivity and catalytic activity. This study presents a new preparation method for producing NiFe 2 O 4 octahedral nanoparticles with the characteristic of low cost, simple process, wide raw material sources, and favorable OER activity, which demonstrates a good application prospect in the field of large-scale hydrogen production. • Low cost NiFe 2 O 4 octahedral nanoparticles are prepared by a facile in-situ etching of stainless steel felt. • The prepared NiFe 2 O 4 octahedral nanoparticles exhibit high catalytic activity and good long-term stability for OER. • NaNO 3 is proved to have the function of removing Cr and promoting the formation of octahedral nanoparticles.

Electronically regulated FeOOH/c-NiMoO4 with hierarchical sandwich structure as efficient electrode for oxygen evolution and hybrid supercapacitors

Electronic regulation via interface engineering is an effective strategy to promote electrochemical performances of nanomaterials. This work reported a facile method to prepare sandwich-like FeOOH/c-NiMoO4 with FeOOH as the mid-layer and the composite of NiMoO4-Ni(OH)2 nanosheets on both sides of FeOOH. Benefiting from the novel hierarchical porous structures and compositional features, the obtained FeOOH/c-NiMoO4 showed excellent electrochemical performances as electrodes for oxygen evolution reaction (OER) and hybrid supercapacitors (HSCs). It demonstrates excellent OER performances with an overpotential of 254 mV to reach the current density of 10 mA cm−2, a Tafel slope of 58 mV dec−1, and a low applied potential difference of 1.51 V at 10 mA cm−2 for overall water splitting and yields a high specific capacity of 1137 C g−1 (specific capacitance of 2273 F g−1) at 1 A g−1 for SCs in an alkaline electrolyte. First-principle calculations were employed to explore the origin. This work manifests the feasibility of rational design of multi-functional materials via electronic modulation for overall water splitting and energy-storage devices.

(Invited, Digital Presentation) Nanostructured Thin Film (NSTF) Iridium Catalyst Powder for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) are electrochemical devices which generate hydrogen (H2) gas from water and electrical energy feedstocks. PEMWEs produce H2 renewably and carbon-free when the electricity is from renewable sources, and are a pathway to enable deep decarbonization across multiple industrial and energy sectors[1]. However, commercial deployment of PEMWEs is currently limited to megawatt-scale due to relatively higher H2 production costs and capital costs than hydrocarbon reforming [2]. The higher costs are due in part to the use of significant quantities of expensive materials (Pt and Ir electrocatalysts and perfluorinated ionomers), insufficient operating performance and durability, and high manufacturing costs. Additionally, commercial PEMWEs additionally use high Ir loadings [3] for the oxygen evolution reaction (OER), and the limited abundance of Ir [4] may limit PEMWE annual deployment of those technologies to gigawatt (GW) scale.3M Nanostructured Thin Film (NSTF) PEMWE OER powder catalysts and electrodes are a unique approach to address the cost and Ir utilization barriers noted above. NSTF catalysts [5] are comprised of nm-scale catalyst metal thin films on a high aspect ratio inert support (Fig. A). NSTF Ir OER catalysts enable high efficiency and high durability due to high OER mass activity and intrinsic resistance to dissolution, imparted by the unique agglomerated thin film catalyst structure. NSTF OER electrodes [6] consist of a dispersed matrix of NSTF catalyst powder particles within a perfluorosulfonic acid (PFSA) ionomer binder (Fig. B), which have high catalyst utilization due to the high electronic conductivity of the primary catalyst particles.One of the key challenges associated with development of OER catalysts and electrodes is the lack of qualified accelerated stress tests (ASTs) to enable rapid assessments of durability under conditions relevant for end-use. The challenge is in part magnified by the long lifetime requirements of 80,000 hours and low required decay rates of single microvolts per hour, which traditionally has required long testing times and multiple replicates to obtain needed statistical significance. Additionally, evaluations of durability have often occurred under steady state testing with fixed current densities, which do not reflect anticipated use profiles when integrated with renewables such as wind and solar with significant power production variability over time. Lastly, operation at increased stack power densities is considered a key strategy to reduce stack capital costs and Ir requirements on a gram per kW basis.In this paper, we will report recent work on our durability assessment of NSTF OER powder catalysts and electrodes under aggressive testing protocols with low catalyst loadings relevant for PEM electrolyzers at large scale. Assessments included steady state durability tests, an accelerated stress test, and a protocol intended to simulate integration with a wind variable renewable energy (VRE) load profile. An example of results from the wind VRE protocol are summarized in Figs. C and D. The wind VRE protocol generated by Alia et al. [7] was modified from voltage control to current control and the maximum current density was scaled to 4.5A/cm2. The protocol was applied to a 3M laboratory CCM comprising a 0.20 mg/cm2 of 78wt% Ir/NSTF powder catalyst OER electrode, 0.09 mg/cm2 of 78wt% Pt/NSTF powder hydrogen evolution reaction (HER) electrode, and a 100 micron thick PEM (800EW 3M PFSA). After 500 hours of the wind VRE protocol, the cell performance was essentially unchanged (1mV voltage decrease at 2A/cm2). S. Dept. of Energy “H2@Scale”, https://www.energy.gov/eere/fuelcells/h2scale.S. Dept. of Energy H2USA Model, Current Forecourt Hydrogen Production v. 3.101.Ayers et al., Catalysis Today 262 121-132 (2016).Babic et al., Electrochem. Soc. 164 F387 (2017).Debe et al., ECS Trans. 45(2) 47-68 (2012).Steinbach et al., 2019 U.S. DOE Annual Merit Review, Project ta026.Alia et al., Electrochem. Soc. 166 F1164 (2019). Figure 1

Ionomer Dispersion for IrO2 Based Oxygen Evolution Reaction Electrode with for Decal Process Application

Green hydrogen production is of importance in the upcoming hydrogen economy era. Proton exchange membrane (PEM) water electrolysis is one of the most important technology to produce the green hydrogen, which requires only water and extra electricity supplied from renewable energy. Main component, i.e., membrane electrode assembly (MEA), is a key part consisting of polymer electrolyte membrane and two electrodes which are oxygen evolution reaction (OER) electrode and hydrogen evolution (HER) electrode. Both electrode should be coated on the surface of membranes for better performance and mass production. HER could be coated by spraying or decal processes since Pt/C electrocatalysts allow to be dispersed in diluted (for spraying) and concentrated (for decal) catalyst inks. However, OER electrode mainly uses IrO2 black electrocatalyst which only allows diluted catalyst inks due to low surface area of IrO2. Thus, OER is generally coated by a spray method. For a decal process for OER electrode, high concentration or high viscosity of catalyst ink should be prepared. In this study, high viscosity ionomer dispersions were prepared using commercially available ionomer dispersions in water and alcohol mixture by substituting water and alcohol solvents into high viscosity solvent (propylene glycol in this study). High viscosity solvent-based ionomer dispersion was investigated for high concentration or high viscosity catalyst ink. The OER electrodes using high viscosity ionomer dispersions were evaluated by electrochemical characterization such as I-V polarization and activation rate. Acknowledgment This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT ＆ Future Planning (NRF-2019M3E6A1063677) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Failure Analysis of Nickel-Coated Anodes in Zinc-Air Hybrid Flow Batteries

A zinc-air flow battery system pumps "fuel” (a zinc particle/KOH slurry) from a fuel tank to a fuel cell stack, where the zinc particles are combined with oxygen from the air to form zincate ions and produce electricity. The zincate-rich electrolyte is then returned to the fuel tank. During the charging cycle, the electrolyte is passed to the zinc regenerator, where electricity (from renewable sources such as solar or wind) is utilized to convert the zincate ions to zinc particles. The regenerated fuel is pumped back into the fuel tank for the discharge process.Nickel is considered for use as the anode during zinc regeneration as it has been shown to be an active catalyst for the oxygen evolution reaction (OER). However, nickel electrodes pose manufacturing challenges due to machinability issues. Alternatively, nickel can be coated on a machinable metal substrate to improve scalability. These electrodes are subjected to open circuit voltage (OCV), OER, and the hydrogen evolution reaction (HER) during operation of zinc-air flow batteries. The electrodes have been observed to fail during prolonged voltage cycling due to nickel coating delamination, which manifests itself as blistering, flaking, and discoloration. It is hypothesized that this may be due to electrolyte penetration into the pores of the nickel coating during operation. The present work is aimed at analyzing and mitigating the coating delamination process through characterization of various Ni coating recipes. As-fabricated and cycled electrodes are characterized using various microstructural techniques, including optical microscopy, x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and x-ray tomography. Coated electrodes are also evaluated electrochemically and the results are correlated with the microstructural analysis. The overall goal of the work is to understand the failure mechanisms and apply the knowledge to fabricate improved coatings for OER electrodes.

Low Cost Electrodes for Alkaline Water Electrolysis

To succeed with the green transition, one must have cheap and reliable ways to store intermittent renewable energy. It is believed that hydrogen will play a key role in this regard, preferably through electrochemical water splitting. Alkaline water electrolysis is a mature technology, using nickel materials in most key components. Although Ni and Ni-S are active materials towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, it is desirably to develop more active, durable and cheaper electrodes through a simple activation procedure of low-Ni containing materials. Moureaux et al. [1, 2] and Schäfer et al. [3] have shown that cheap stainless steel electrodes can be activated through electrooxidation in high pH electrolytes creating a nickel enriched surface.In this work we have employed a similar activation procedure, activating SS316 at 1.7 V for 18 hours at room temperature in a 3-electrode electrochemical cell using electrolytes with various KOH concentrations. The surface composition was analyzed with XPS and GD-OES before and after activation, and revealed that the Ni content in the surface increased with increasing KOH, at the expense of Fe and Cr. The composition converged to 73% Ni and 27% Fe for KOH concentration of 7.5 and higher. This composition showed the best OER performance of all surfaces prepared, including pure Ni electrodes. A similar enrichment of Ni was observed for SS304, reaching the same surface composition as SS316. However, the Ni content in the surface after activation changed less and was lower than SS316 and SS304 after activation for plate materials with higher nominal Ni bulk composition (Inconel718, Incoloy800 and NiFe 50:50 alloy). Hence, the surface composition can be tuned by selecting an electrode material and pH of the activation electrolyte.Furthermore, we have tested the activated SS316 electrodes at relevant operating conditions in a single cell alkaline water electrolyzer test rig (30wt% KOH, 80°C and 9 bar) and compared it with Ni and as-received SS316 electrodes. The activated SS316 electrodes outperformed the other electrodes and showed a stable performance during 255 hours operation at 0.8 A cm-2. The OER electrode activation procedure was successfully attempted in-situ in the alkaline single cell water electrolyzer test rig. However, the application of high currents needed for the activation led to high cell voltages (3 V) and hence harmful conditions.Finally, the effect of the activation procedure on the HER performance was also investigated and tied to the purity of the electrolyte. Deposition of Cu and Fe metal impurities was observed on the HER electrode, which increased with a lower grade of the KOH electrolyte. HER activity was observed to increase after activation in low grade KOH, which was attributed to an increased surface area and higher Fe to Cu ratio in the deposit.[1] F. Moureaux, P. Stevens, G. Toussaint, M. Chatenet, J. Power Sources 229 (2013) 123-132.[2] F. Moureaux, P. Stevens, G. Toussaint, M. Chatenet, Appl. Catal. B-Environ 258 (2019) 117963.[3] H. Schäfer, D.M. Chevrier, P. Zhang, J. Stangl, K. Müller‐Buschbaum, J.D. Hardege, K. Kuepper, J. Wollschläger, U. Krupp, S. Dühnen, Adv. Funct. Mater. 26 (2016) 6402-6417.

Low‐cost Trimetallic Ni‐Fe‐Mn Oxides/(Oxy)hydroxides Nanosheets Array for Efficient Oxygen Evolution Reaction

AbstractThe development of low‐cost, efficient, and stable water oxidation electrocatalyst is of great importance for hydrogen production. Herein, we report an approach to convert commercial stainless steel plate (SSP) into trimetallic Ni‐Fe‐Mn oxides/hydroxides nanosheets (NiFeMnOxHy‐SSP) as an oxygen evolution reaction (OER) electrode. The NiFeMnOxHy‐SSP exhibits excellent OER performance with an overpotential of 232 mV at 10 mA cmgeo−2, a Tafel slope of 37.6 mV dec−1, and long‐term stability (100 h) in 1.0 M KOH aqueous solution. The electrochemical results reveal that the Mn plays a significant role in reducing overpotential and improving stability at 500 mA cmgeo−2 for OER. This work provides a facile way to fabricate OER electrodes by surface modification of SSP towards industrial water splitting.

Molecular Regulation Based on Functional Trimetallic Metal-Organic Frameworks for Efficient Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) as classic crystalline porous materials have attracted great interest in the catalytic field. However, how to realize molecular regulation of the MOF structure to achieve a remarkable oxygen evolution reaction (OER) electrocatalyst is still a challenge. Herein, we designed several series of special MOF materials to explore the relationship between the structure and properties as well as the related reactive mechanism. First, various metal centers, including Fe, Co, Ni, Zn, and Mg, were utilized to construct the first series of trimetallic MOF materials, namely, M3-MOF-BDC, where BDC = 1,4-benzenedicarboxylic acid, also known as terephthalic acid. Among of them, Fe3-MOF-BDC shows the best OER performance and only needs an overpotential of 312 mV at 10 mA cm-2. Then, functional BDC-X ligands (X = NH2, OH, NO2, DH) with various characteristic groups were selected to construct a new series, namely, Fe3-MOF-BDC-X, to further improve its OER electrocatalytic performance. As expected, Fe3-MOF-BDC-NH2 exhibited a greatly enhanced OER performance with ultralow Tafel slopes of 45 mV dec-1 and overpotentials of 280 mV at 10 mA cm-2 when the BDC-NH2 ligand was adopted, even superior to commercial IrO2 (323 mV) and most of the reported pristine MOFs as OER electrodes. Much higher structural stability was proven. The detailed structure-property relationship and mechanism are discussed. In a word, this work provides a very important theoretical basis for the design and exploration of new MOF electrocatalysts.