Oxygen Evolution Electrode Research Articles

Highly Active Nano-Porous Thin-Films for Water Electrolysis Using an Automated Print Technology Based on Spark Ablation

Accelerating hydrogen (H2) deployment via renewable electricity is a key G7 strategy for sustainable transitions in hard-to-decarbonize sectors (e.g., circular-plastics, -steel, -fertilizers,shipping, and aviation) therefore, Alkaline (AWE) and Polymer Electrolyte Membrane water electrolysis (PEMWE) play a crucial role amongst low-temperature power-to-X technologies for establishing a hydrogen network. Assuming all hydrogen will be green by 2030 (with ca. 150 million metric tons), a significant increase in electrolyser capacity to 3,000 gigawatts is necessary, given the current capacity of 0.3 gigawatts. However, the adoption of electrolysers faces a bottleneck due to scarce platinum group materials (PGMs) used as catalyst, specifically Iridium and Platinum. The commercial PGM loading per membrane electrode assembly (MEA) is at 3 mg/cm2, requiring substantial efforts to redesign electrocatalyst materials through a nano-architecture, necessitating a thousandfold increase in surface area (µm to nm scale) and a tenfold reduction in mass loading (mg to µg). The realization of this objective is conceivable through innovative surface engineering and manufacturing techniques, exemplified by. VSPARTICLE is actively advancing its manufacturing technology for green H2, bridging academia and industry . We developed a unique nano-printing technology which utilizes spark ablation for generating nano-porous electrocatalyst thin films across diverse elements and alloys. Unlike traditional methods, it eliminates the need for chemical precursors or binders, reducing waste and extra pre- / post-process steps. The VSP-P1 nano-printer serves as a crucial R&D tool for dry-synthesis, enabling both the production of complex electrocatalyst layers and also sample arrays high-throughput screening. This accelerates the discovery of new catalysts, fostering the creation and application of novel nanomaterials in specialized setups. Our oral presentation will unveil the latest findings concerning oxygen evolution electrodes, employing Ir-based and Ni-based catalysts produced through the innovative VSP-P1 nano-printing technology, which exhibit notable activity in acidic and alkaline water electrolysis, respectively, even at low loadings, such as 0.4 mg/cm2. Therefore, our oral presentation aims to show the latest findings on accelerated electrocatalysts discovery concerning oxygen evolution reaction (OER) produced through the innovative VSP-P1 nano-printing technology. In parallel to comprehensive flow-cell experiments, meticulous control tests and characterization techniques (XRD, XRF, HR-SEM) on proxy samples were conducted, leveraging the versatility of VSP-P1 to create identical nano-porous films on various substrates such as Si-wafer, conductive glass, and glassy carbon disks. The scalability of this dry manufacturing process, coupled with the rapid iteration capability for tuning material parameters and test-beds, promises a tenfold acceleration in electrocatalyst utilization. In summary, this presentation intends to reveal a methodology that not only shows an efficient strategy for catalyst utilization through nano-printed layers, but also shortens the time required to bring novel materials to market. Figure 1

Facile top-down fabrication of integrated amorphous NiFe-based electrocatalytic electrodes for high current and long-life oxygen evolution

Developing an industrially relevant electrode with high catalytic activity, stability, and tunable composition/size for large-scale water electrolysis is a significant challenge. We have created an integrated electrode (NFM30-N) for the oxygen evolution reaction (OER) using a facile top-down approach that combines arc melting with dealloying-oxidation. Due to the dealloying-oxidation effect, the as-derived porous amorphous M–O, M–OH, and M–OOH (M = Ni, Fe) nanocones cover the basic NiFeMn alloy. This integrated design enables NFM30-N to exhibit outstanding OER performance at high current densities, requiring low overpotentials of only 282 and 323 mV to achieve large current densities of 100 and 500 mA cm−2, respectively. It also displays a small Tafel slope of 44.1 mV dec−1 and remarkable stability for over 100 h at 100 and 500 mA cm−2. When used as an anode, a two-electrode electrolyzer cell with NFM30-N at 500 mA cm−2 only requires a cell voltage of 1.619 V and exhibits excellent stability, with almost no performance degradation after continuous chronopotentiometry test for each 100 h at 500 and 100 mA cm−2. This exceptional OER electrocatalytic performance is attributed to the integrated structure providing high electrical conductivity and stability, the presence of numerous active sites due to dealloying and the amorphous structure, and the promotion of the OER process by M–O, M–OH, and M–OOH species. This work offers a novel idea for fabricating integrated, industrially relevant electrocatalytic electrodes through traditional metallurgy combined with dealloying-oxidation.

Impact of applied potential range on corrosion behavior of stainless steel oxygen evolution electrode under potential cycle loading

We investigated the corrosion behavior of 310S stainless steel anode for alkaline water electrolyzer under various triangle-wave potential cycle loadings by changing the lower (x) and higher (y) vertex potentials to simulate the power fluctuation characteristics of renewable energy sources. The anode was subjected to the loadings of x = 0.5–1.5 and y = 1.8–2.5 V in 7 M KOH solution. The dissolution of Fe and Cr into the electrolyte depended significantly on x. Notably, under conditions of x ≥ 1.35 V, the total dissolution amounts of Fe and Cr after the 20,000 potential cycles decreased to approximately 7 % of the condition where x = 0.5 V. Conversely, y had less influence on the total dissolution amounts. Interestingly, the molar ratios of the eluted Fe and Cr into the electrolyte depended on both x and y, suggesting distinct corrosion behaviors of the stainless steel induced by the potential cycles of x ≤ 1.35 and y = 1.8 V, compared to those at x ≥ 1.35 and y = 2.5 V. These findings suggest the importance of precise potential control of the stainless steel anode in alkaline water electrolysis for preventing potential fluctuation-induced corrosion.

NiFeCo alloy nanoparticles composited with phosphorus-doped vacancies-abundant carbon substrates as electrocatalyst for oxygen evolution reaction

Transition metal alloy nanoparticles are cost-effective electrocatalysts for oxygen evolution reactions. Preparing alloy catalysts with flexible controllability, high activity, and long-term stability is a challenge. By adjusting the proportion of metal atoms and engineering vacancies through their composite with a carbon substrate, we can enhance electron transfer and modulate the adsorption capacity of reaction intermediates. Herein, we synthesized a hybrid catalyst using Prussian blue analogs (PBAs) as the precursor, doped with Fe and Ni atoms, and subjected them to a defective engineering and phosphatization process. As an efficient alkaline OER electrocatalyst, the formation of the alloy increases the number of active sites, while the defect-rich phosphorus-doped carbon substrate improves internal electron transfer and mass transfer channels. The synthesized NiFeCoPC-1.5 electrocatalyst exhibits excellent catalytic activity with an overpotential of 211 mV at 10 mA cm−2 and a Tafel slope of 59 mV dec−1, and demonstrates good stability up to 1000 CV cycles. This work will expand the application of alloy nanoparticles in oxygen evolution electrodes.

Self-supporting nanosheet electrode for efficient oxygen evolution in a wide pH range: engineering electronic structure of Co3O4 by Fe doping

Self-supporting nanosheet electrode for efficient oxygen evolution in a wide pH range: engineering electronic structure of Co3O4 by Fe doping

In-Site Growth of Efficient NiFeOOH/NiFe-LDH Electrodes: A Streamlined One-Step Methodology

Oxygen evolution reactions (OER) are often the decisive step in determining the water electrolysis rate. The first row of transition metals and their derivatives, represented by Ni and Fe, have attracted much attention due to their excellent OER performance. Here, we develop a one-step strategy for preparing oxygen-evolving electrodes, in which the NiFeOOH-modified NiFe layered double hydroxide (NiFe-LDH) nanosheet is supported by nickel foam. At 100 mA·cm−2, the overpotential of NiFeOOH-NiFe-LDH was just 227 mV, and the duration times were over 200 h in 1 mol·L−1 KOH. Furthermore, the co-existence of LDH and hydroxyl oxides helps the oxygen evolution reaction. These results suggest the potential for this synthesis strategy to provide a low-cost, highly active OER electrocatalyst for industrial water splitting.

Nickel and Commercially Available Nickel‐Containing Alloys as Electrodes for the Electrochemical Oxygen Evolution

AbstractWater electrolysis is a crucial technology for independency on fossil fuels. However, water splitting is limited by the sluggish kinetics of oxygen evolution reaction (OER). While many studies report highly active, non‐precious metal‐based electrocatalysts for alkaline OER, applicability under industrial conditions is often omitted. Such conditions require catalysts being applied on nickel or nickel‐containing alloys in elevated electrolyte concentrations. In contrast to the rather inert substrates often used in scientific studies, such industrially applied substrates exhibit significant OER activity themselves and show dynamic behaviour. Therefore, it is crucial to understand the OER behaviour of such substrates. Here, nickel and seven commercially available nickel‐containing alloys are investigated as anodes in alkaline OER and their elemental compositions correlated to their corresponding activities. Repeated potential cycling across the Ni(II)/Ni(III)‐redox couple is established as activity‐enhancing procedure. Overall, the nickel‐base alloy Hastelloy® X exhibits the highest activity due to its Fe‐, Cr‐, Mo‐ and Co‐content. Though, the activity gain differs significantly for the various materials. Comparing Ni and Hastelloy® X as least and most active materials, the positive impact of activation on both activity and stability becomes evident. While untreated Ni suffers from poor OER stability, the activity‐enhancing procedure also significantly increases electrode stability in 24 h chronopotentiometry.

Fe-Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media.

NiFe-based oxo-hydroxides are highly active for the oxygen evolution reaction but require complex synthesis and are poorly durable when deposited on foreign supports. Herein we demonstrate that easily processable, Earth-abundant and cheap Fe-Ni alloys spontaneously develop a highly active NiFe oxo-hydroxide surface, exsolved upon electrochemical activation. While the manufacturing process and the initial surface state of the alloys do not impact the oxygen evolution reaction performance, the growth/composition of the NiFe oxo-hydroxide surface layer depends on the alloying elements and initial atomic Fe/Ni ratio, hence driving oxygen evolution reaction activity. Whatever the initial Fe/Ni ratio of the Fe-Ni alloy (varying between 0.004 and 7.4), the best oxygen evolution reaction performance (beyond that of commercial IrO2) and durability was obtained for a surface Fe/Ni ratio between 0.2 and 0.4 and includes numerous active sites (high NiIII/NiII capacitive response) and high efficiency (high Fe/Ni ratio). This knowledge paves the way to active and durable Fe-Ni alloy oxygen-evolving electrodes for alkaline water electrolysers.

Ni/Fe based electrocatalyst for highly-efficient anion exchange membrane water electrolysis

Anion exchange membrane water electrolysis (AEMWE) is a feasible pathway to industrial-scale production of hydrogen due to the use of low cost, non-precious metal catalysts. In this study, we demonstrate a stable NiFe2O4 anodic oxygen evolution reaction (OER) catalyst to achieve durable and efficient AEMWE via a simple strategy combining hydrothermal and thermal reduction reactions. The prepared NiFe2O4-50 catalyst, with polyhedral-sphere hybrid morphology and abundant oxygen vacancies, exhibits an overpotential of 280 mV at 50 mA cm−2 and a Tafel slope of only 44.6 mV dec−1 for OER. Moreover, its use as oxygen evolution electrode in AEMWE cell assembled with a Pt/C cathode show excellent water electrolysis performance with a current density of high to 4 A cm−2 at 1.89 V, a cell voltage of only 1.64 V at 1 A cm−2, as well as good long-term stability over >1000 h of continuous water electrolysis under a current density of 1 A cm−2. The newly developed NiFe2O4 catalyst demonstrates excellent AEMWE performance and has a potential application for practical large-scale hydrogen production.

The Structure-Performance Relation for Alkaline OER Electrocatalyst Investigated Using Analytical Electron Microscopy

Water electrolysis technology plays a key role in reducing carbon emission by converting renewable energy to clean hydrogen. Among various types of electrolyzers, anion exchange membrane water electrolyzer (AEMWE) receives growing effort of research due to its potential of comparable power density as its counterpart, proton exchange membrane water electrolyzer (PEMWE), while offering less corrosive environment on the oxygen evolution electrode which permits the use of non-noble metal catalysts [1].Nickel-iron oxides/hydroxides are among the most active electrocatalysts for oxygen evolution reaction (OER) in alkaline environment [2]. Recently, aerogel-like Ni-Fe oxides developed at Los Alamos National Laboratory have shown promising performance in AEMWE. The modified sol-gel approach followed by drying under supercritical condition produces high-surface-area oxides which likely contributes to high OER activity with enhanced number of active sites compared to other synthesis methods [3].In this work, we aim to elucidate the structure-performance relation for aerogel-like Ni-Fe oxides. Analytical electron microscopy methods, namely, energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) are used to investigate the distribution of Fe in the oxides and the oxidation states of Ni and Fe. The effect of annealing temperature in air on the oxide structure and OER activity has been investigated. Moreover, the structural changes before and after catalyst activation and long-term operation at OER potentials have been studied. Finally, results from analytical electron microscopy have been correlated with X-ray absorption spectroscopy and 57Fe Mossbauer spectroscopy to obtain a comprehensive picture of the oxide composition, especially the chemical environment of Fe.

(Invited) Impact of Phenyl Adsorption of Various Ionomers on the Performance of Anion Exchange Membrane Water Electrolyzers

In this presentation, design principals of ionomeric binders for anion exchange membrane water electrolysis (AEMWE) will be discussed. The crucial impact of phenyl adsorption on AEMWE performance is highlighted with poly(terphenylene), poly(fluorene), poly(aryl piperidinium), or polynorbonene ionomers. Adsorption energies to hydrogen oxidation catalyst surfaces, calculated by density functional theory, demonstrate the utility in the phenyl free ionomer structure wherein lower adsorption energies yield improved AEMWE performance.1,2 Polarization curves with higher adsorption energy ionomers show a nonlinear transition to mass transport limited behavior at cell potentials above 1.68 V. Alternatively, mass transport limitations are absent when using the phenyl free ionomer, polynorbonene.3 Furthermore, polarization curves in 1 M NaOH of all studied systems begin to overlap suggesting that the phenyl oxidation on the oxygen evolution catalyst may be a primary influence on the transition to mass transport limits in AEMWE. Recent progress in both ionomer and AEM development at LANL for improved performance and durability of AEMWE, specifically with regard to limiting phenyl oxidation, will be discussed.1 Matanovic, I. et al. Adsorption of Polyaromatic Backbone Impacts the Performance of Anion Exchange Membrane Fuel Cells. Chemistry of Materials 31, 4195-4204, doi:10.1021/acs.chemmater.9b01092 (2019).2 Motz, A. R. et al. Performance and durability of anion exchange membrane water electrolyzers using down-selected polymer electrolytes. Journal of Materials Chemistry A 9, 22670-22683, doi:10.1039/D1TA06869E (2021).3 Huang, G. et al. Ionomer Optimization for Water Uptake and Swelling in Anion Exchange Membrane Electrolyzer: Oxygen Evolution Electrode. Journal of The Electrochemical Society 167, 164514, doi:10.1149/1945-7111/abcde3 (2020).

Catalyst Application in Three-Dimensional Porous Electrodes for Alkaline Electrolysis

Hydrogen is critical in the green transition, and a key system for producing green hydrogen is through alkaline electrolysis. Although the alkaline electrolyzers are mature and commercially available, vast improvements are still expected in the future 1.Traditional and most commercially applied alkaline electrolyzer electrodes are made from massive nickel plates (or nickel-plated steel plates) with some scattered perforation. With the ongoing development of thin alkaline ion‐conducting membranes with low internal resistance, the benefit of three‐dimensional porous electrodes becomes obvious. With such electrodes, there will be no blind spots and the active catalytic area can be increased significantly. Today, most groups developing such 3D electrodes use commercial nickel foam as substrate. This limits the options to what is available in the market, moreover the purchase cost is high.The present work aims at developing high‐performing three‐dimensional hydrogen and oxygen evolution electrodes for alkaline electrolysis. The focus will be on the application of nanostructured electrocatalysts into three‐dimensional electrode structures, similar to nickel foams.The results obtained, so far, show homogeneous formation of nanoparticles on the surface. The analysed samples show mechanical flexibility as soon as the particles are deposited but samples become rigid after testing in a half cell setup with KOH 1 M electrolyte. Further analysis will explore changes to the microstructure. The roughness factor calculated by non-faradaic cyclic voltammetry is in the range of 75 cm2 ECSA / cm2geometric, showing higher value than the commercial Nickel foam.Initial experiments are carried out on as-prepared samples, but more advanced catalysts are also explored based on state-of-the-art materials. [1] IRENA - Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5 °C Climate Goal, International Renewable Energy Agency, Abu Dhabi (2020)

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.

Fabrication of Nanostructured Catalyst Layers on Stainless Steel and Its Application to the Oxygen Evolution Electrode for Alkaline Water Electrolysis

Fabrication of Nanostructured Catalyst Layers on Stainless Steel and Its Application to the Oxygen Evolution Electrode for Alkaline Water Electrolysis

Electronically Conductive, Multifunctional Polymer Binder for Highly Active, Stable, and Abundant Composite Electrodes for Oxygen Evolution

The electrolysis of water to form hydrogen and oxygen is a promising method to store renewable energy. This method requires electrodes that convert water into protons, electrons, and oxygen. We report a multifunctional polymer that conducts electrons and ions and may coreact with the electrocatalyst in the oxygen evolution reaction (OER). The electrodes were prepared in two steps from off-the-shelf reagents. They operate with low loadings of abundant catalysts and are among the most active (100 mA cm-2 at 1.43 V vs RHE (1.41 V, iR-corrected)) and stable electrodes, reported to date under harsh conditions (85 °C, 6 M KOH, 120 h (0.69% loss over the first 14.5 h and then 0.61% loss over 105.5 h)). Control experiments on glassy carbon electrodes showed that the polycarbazole system significantly outperformed a Nafion system of the same catalyst loading. This simple strategy can be applied to other types of electrodes.

Wood‐Derived, Monolithic Chainmail Electrocatalyst for Biomass‐Assisted Hydrogen Production

AbstractThe chainmail catalyst by encapsulating an active species within the carbon support is a well‐established concept to endorse extraordinary stability for catalytic reactions under harsh conditions. Conventional chainmail catalysts inevitably suffer from poor accessibility to active sites, leading to extra voltage to compensate the sluggish diffusion kinetics in electrocatalysis. Herein, the naturally abundant wood material is converted into a monolithic chainmail electrocatalyst by encapsulating cobalt nanoparticles within N‐doped carbonized wood. Such a monolithic chainmail catalyst is employed directly as electrode for hydrogen evolution (HER), oxygen evolution (OER), and monosaccharide oxidation reactions (MOR) with benchmark performance. By coupling the HER with MOR, the electrolyzer equipped with the monolithic chainmail catalyst allows hydrogen production at a current density of 100 mA cm−2 with a full cell voltage of only 1.36 V. Such design of wood‐derived chainmail catalyst provides a promising way to fabricate robust electrocatalysts for future production of hydrogen and value‐added chemicals.

Suppression of Catalyst Layer Detachment by Interfacial Microstructural Modulation of the NiCo2O4/Ni Oxygen Evolution Electrode for Renewable Energy-Powered Alkaline Water Electrolysis.

Alkaline water electrolysis (AWE) is a large-scale hydrogen production technology. A major degradation mode of AWE when using fluctuating power derived from renewable energies is the detachment of the catalyst layer (CL). Here, this study investigates the CL detachment mechanism of NiCo2O4-CL-coated Ni (NCO/Ni) electrodes under an accelerated durability test (ADT) simulating a fluctuating power and the effect of post-annealing on detachment behavior. Microstructural analysis reveals that detachment begins at the nanoscale gaps between the stacked CLs and between CL and the substrate. Post-annealing at 400 °C removes the degradation starting point in CL, and a composition gradient Co-doped NiO interlayer and NiO(111)/Ni(111) epitaxial interface form between CL and the Ni substrate, nearly suppressing CL detachment. Although the electrode performance of the annealed sample is initially lower than that of the as-prepared sample, the overpotential is significantly reduced during ADT due to the formation of the NiCo hydroxide active surface layer. These results demonstrate that interfacial microstructural modulation by post-annealing is a powerful approach to realizing durable electrodes for green hydrogen production by renewable energy-powered AWE.

Self-adhesive ionomers for alkaline electrolysis: Optimized oxygen evolution electrode

Self-adhesive ionomers for alkaline electrolysis: Optimized oxygen evolution electrode

Plasma nitrided CoCrFeNiMn high entropy alloy coating as a self-supporting electrode for oxygen evolution reaction

Noble metal electrocatalytic electrodes used in water electrolysis for hydrogen production are expensive and non-noble metal nanoparticle catalysts are not conducive to large-scale production. In this paper, the CoCrFeNiMn high entropy alloy (HEA) coating was prepared by high-velocity oxygen fuel (HVOF) spraying on the surface of stainless steel as a self-supporting oxygen evolution electrode, and the electrocatalytic activity of the electrode was further improved by plasma nitriding. The results show that the CoCrFeNiMn coating is mainly composed of FCC solid solution phase and MnCr2O4 spinel phase, and the thickness of the coating is approximately 100 μm. After nitriding, the surface of the coating is reshaped from the original semi-molten morphology to cauliflower-like structure, and the N atoms are mainly enriched in the MnCr2O4 phase. In addition, the binding energies of Co, Cr, and Ni to O in the nitrided coating decrease by 0.7 eV, while the binding energies of Fe and Mn to O are not significantly affected. The overpotential of the nitrided CoCrFeNiMn coating decreases from 363 mV to 309 mV at the current density of 10 mA cm−2, and it has a smaller Tafel slope and charge transfer resistance, and larger double-layer capacitance compared to the CoCrFeNiMn coating. Both the CoCrFeNiMn coated electrodes with and without nitriding show good long-term stability during the 60 h stability test. The high entropy alloy coating coupled with plasma nitriding technique provides a new research idea for the eletrocatalytic field of the water splitting.

In situ self-assembled macroporous interconnected nanosheet arrays of Ni-1,3,5-benzenetricarboxylate metal − organic framework on Ti mesh as high-performance oxygen evolution electrodes

Highly efficient metal–organic framework (MOF)-based oxygen evolution reaction (OER) catalysts are desirable for water splitting, but their development remains challenging due to poor accessibility of coordinatively unsaturated metal (cum) sites and low intrinsic activity. A large-area three-dimensional (3-D) macroporous interconnected nanosheet array of Ni-1,3,5-benzenetricarboxylate has been in situ self-assembled on Ti mesh (TM) by using ethanol as the solvent and high-affinity oxide layer on TM to promote in situ nucleation. The obtained nanoarchitecture exhibits much superior catalytic activity compared to most reported catalysts including MOF-based catalysts, other precious-metal-free ones, and Ir/Ru-based ones. Additionally, this electrode undergoes no current decay after 300 cyclic voltammetry (CV) cycles and can maintain at 250 mA cm−2 for over 266 h. The excellent catalytic performance is mainly due to the 3-D macroporous and interconnected nanosheet array structure improving cum site exposure and charge transport and in situ activated cum cations enhancing OH− adsorption. This work not only develops a facile and economical approach to synthesize 3-D macroporous interconnected MOF nanosheet arrays to simultaneously increase the number, exposure, and intrinsic activity of active sites and facilitate charge transport for high-performance eletrocatalysis, but provides scientific insights into the mechanisms for self-assembly of this unique nanoarchitecture and for the high OER performance.