Catalytic Microenvironment Research Articles

Ionomer and Membrane Designs for Low-temperature CO2 and CO Electrolysis.

Low-temperature electroreduction of CO2 and CO (CO(2)RR) into valuable chemicals and fuels offers a promising pathway to reduce greenhouse gas emissions and achieve carbon neutrality. Today's low-temperature CO(2)RR technology relies on the use of ionomers, polymers with ionized groups, primarily as catalyst layer (CL) additives. In the meantime, ionomers can assemble into ion-exchange membranes (IEMs), serving as important components of electrolyzers. According to the ion-exchange functions, ionomer additives are classified as cation-exchange ionomers (CEIs) and anion-exchange ionomers (AEIs); similarly, IEMs are divided into cation-exchange membranes (CEMs) and anion-exchange membranes (AEMs), as well as the multilayer polymer electrolytes (MPEs). Recent studies show that ionomer additives can regulate the catalytic microenvironment and thereby enhance performance towards desired products. This Review discusses the roles of ionomer additives and IEMs in CO2 and CO reduction reactions, highlighting the latest mechanistic insights and performance advances. It outlines challenges in designing ionomer additives and IEMs to improve product selectivity, energy efficiency (EE), and operational lifetime of CO(2)RR electrolyzers, while also providing perspectives on future research directions. The aim is to connect the current status of ionomer and membrane development with performance metrics analysis, offering insights for the advancement of commercially relevant low-temperature CO(2)RR electrolyzers.

Engineering Catalytic Microenvironment Enabling Direct Carbonate Electrolysis to Ethylene

Engineering Catalytic Microenvironment Enabling Direct Carbonate Electrolysis to Ethylene

Tailoring the local catalytic microenvironment of metal centers NH2 groups to enhance the CO2RR performance of Ni based catalysts

Efficient catalytic reduction of the main greenhouse gas CO2 into high value-added chemicals is an important measure to alleviate the greenhouse effect and energy depletion. Metal nitrogen (M-N4) macrocyclic complexes have attracted increasing attention in the field of electrocatalytic CO2 reduction (CO2RR) due to the precise adjustment of the catalytic active site according to the requirements and the flexible modification of the external ligand structure. Nevertheless, the poor activity and low selectivity of reduction products restrict their widespread application in electrocatalytic CO2RR. Herein, a combination of nanoscale and molecular level method has been developed to construct easily obtainable 4NH2-NiPc/NH2-CNT hybrid material, in which amino groups are connected to provide electrons toward the central Ni-N4 site to promote the electrocatalytic CO2RR catalytic activity. As a result, the catalyst 4NH2-NiPc/NH2-CNT mainly produces CO in the electrocatalytic CO2RR, which exhibits a Faradaic efficiency of CO (FECO) higher than 92 % within a wide overpotential range of −0.70 to −0.95 V vs. RHE, and provides excellent stability with a current density of 12 mA cm−2 at −0.80 V vs. RHE. In addition, 4NH2-NiPc/NH2-CNT reaches its maximum FECO value of 96 % at −0.8 V vs. RHE, which is approximately 3.1 times that of the original unmodified NiPc/CNT, demonstrating excellent promotion of electrochemical performance. Similarly, compared to NiPc/CNT without amino modification, the current density of 4NH2-NiPc/NH2-CNT exceeds it by more than twice. The research results indicate that promoting role of electron substituted amino groups in catalysis dispersion and electronic environment coordination. This study proposes a promising strategy of introducing amino groups into molecular catalysts and hybridizing with carbon nanotube to enhance the electrocatalytic conversion of CO2 to deep reduction products.

Molecularly Woven Cationic Covalent Organic Frameworks for Highly Selective Electrocatalytic Conversion of CO2 to CO.

Coupling carbon capture with electrocatalytic carbon dioxide reduction (CO2R) to yield high-value chemicals presents an appealing avenue for combating climate change, yet achieving highly selective electrocatalysts remains a significant challenge. Herein, two molecularly woven covalent organic frameworks (COFs) are designed, namely CuCOF and CuCOF+, with copper(I)-bisphenanthroline complexes as building blocks. The metal-organic helical structure unit made the CuCOF and CuCOF+ present woven patterns, and their ordered pore structures and cationic properties enhanced their CO2 adsorption and good conductivity, which is confirmed by gas adsorption and electrochemical analysis. In the electrocatalytic CO2R measurements, CuCOF+ decorated with extra ethyl groups exhibit a main CO product with selectivity of 57.81%, outperforming the CuCOF with 42.92% CO at the same applied potential of 0.8 VRHE. After loading Pd nanoparticles, CuCOF-Pd and CuCOF+-Pd performed increased CO selectivity up to 84.97% and 95.45%, respectively. Combining the DFT theoretical calculations and experimental measurements, it is assumed that the molecularly woven cationic COF provides a catalytic microenvironment for CO2R and ensures efficient charge transfer from the electrode to the catalytic center, thereby achieving high electrocatalytic activity and selectivity. The present work significantly advances the practice of cationic COFs in real-time CO2 capture and highly selective conversion to value-added chemicals.

Enhancing Biocatalysis through Chiral Supramolecular Scaffolds: Insights into the Structural Adaptability of Lipase.

How to maintain high catalytic activity and stability in the process of biocatalysis is crucial, inspiring strategies to construct an appropriate catalytic microenvironment. Considering the lipase's inherent chirality and the necessity for a delicate hydrophilic-hydrophobic equilibrium, we crafted a chiral, nonaqueous catalytic microenvironment via the in situ coassembly of Boc-FLFL-NHNH2 (Bfl) and lipase. Benefiting from the chirality and distinct Bfl-lipase interactions, the lipase@Bfl supramolecular hybrid amplifies biological functionalities and can serve as a versatile and highly efficient catalyst. Kinetic investigations and molecular docking simulations uncover the strong lipase-substrate affinity and lipase-Bfl interactions, explaining the enhanced biological effects, catalytic activity, and stability. Our study establishes a suitable microenvironment to address the chirality and hydrophobicity during catalysis and highlights the potential of artificial chiral scaffolds and catalytic medium for enhancing lipase activity.

The Hydrogen Evolution Reaction: Using Molecular Design in Transition Metal Complexes to Control Catalytic Microenvironments on Electrode Surfaces

AbstractHydrogen gas and its production from renewable power sources will be an important part of decreasing global reliance on fossil fuels and developing a sustainable energy economy. Efficient electrocatalysis, however, relies on the delivery of both protons and electrons; ideally in a concerted fashion to avoid high energy intermediates, prevent charge build‐up, and circumvent large kinetic barriers. While this can be achieved using ligand design in homogenous molecular transition metal catalysts (specifically incorporating proton shuttles in the secondary coordination sphere), heterogeneous systems are more desirable from an industrial perspective due to their ease of use and enhanced durability. Supporting transition metal catalysts on electrode surfaces is therefore a promising approach for developing next generation electrocatalysts that retain molecular level control in interfacial environments. This review will first cover key design principles from natural systems, such as hydrogenase enzymes, and then survey some representative examples of synthetic homogeneous hydrogen evolution electrocatalysts that incorporate these important features. We will then discuss transition metal species that have been supported on electrode materials, with a focus on recent advances in the field, and the major challenges that remain.

Hydrophobic-treated yolk-shell SnS2@CSs Z-scheme confinement reactor for solar-electro-driven hydrogen peroxide production in neutral media

The diffusion and adsorption properties of the O2/H2O corpuscles at active sites play a crucial role in the fast photo-electrocatalytic reaction of hydrogen peroxide (H2O2) production. Herein, SnS2 nanosheets with abundant interfacial boundaries and large specific areas are encapsulated into hollow mesoporous carbon spheres (CSs) with flexibility, producing a yolk-shell SnS2@CSs Z-scheme photocatalyst. The nanoconfined microenvironment of SnS2@CSs could enrich O2/H2O in catalyst cavities, which allows sufficient internal O2 transfer, improving the surface chemistry of catalytic O2 to O2− conversion and increasing reaction kinetics. By shaping the mixture of SnS2@CSs and polytetrafluoroethylene (PTFE) on carbon felt (CF) using the vacuum filtration method, the natural air-breathing gas diffusion photoelectrode (AGPE) was prepared, and it can achieve an accumulated concentration of H2O2 about 12 mM after a 10 h stability test from pure water at natural pH without using electrolyte and sacrificial agents. The H2O2 product is upgraded through one downstream route of conversion of H2O2 to sodium perborate. The improved H2O2 production performance could be ascribed to the combination of the confinement effect of SnS2@CSs and the rich triple phase interfaces with the continuous hydrophobic layer and hydrophilic layer to synergistically modulate the photoelectron catalytic microenvironment, which enhanced the transfer of O2 mass and offered a stronger affinity to oxygen bubbles. The strategy of combining the confined material with the air-breathing gas diffusion electrode equips a wide practical range of applications for the synthesis of high-yield hydrogen peroxide.

Tailoring the catalytic microenvironment of CuO with hydrophobic CuSA2 for selective CO2 electroreduction to C2+ products

Advancing the Faraday efficiency (FE) and current density of Cu catalyzed electrochemical CO2 reduction (ECR) reaction to produce C2+ products is important for its practical applications. Constructing a hydrophobic interface to regulate the local reaction environment is an effective method to improve the selectivity of C2+ products, but it is limited by the low reaction current density. In this work, we fabricated a novel hydrophobic and ECR active copper stearate (CuSA2) decorated CuO nanoparticle catalyst (CuO/CuSA2) for ECR reaction toward C2+ products. As a result, the CuO/CuSA2 catalyst achieved an FE of 61.33 % and a partial current density of 429.33 mA cm−2 for C2+ products. The CuSA2 and CuO nanoparticle cooperate very well for the formation of C2+ products. The in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and electrochemical adsorption experiment indicated that the hydrophobic CuSA2 regulated the local ECR reaction environment. The local ∗CO2.- and *CO adsorption were strengthened by hydrophobic CuSA2 modification while the H2O adsorption was inhibited. CuO nanoparticle promotes *CO coupling reaction and enhances C2 intermediates (*OCCOH and *OC2H5) adsorption. Hydrophobic CuSA2 and CuO nanoparticle synergistically promote the generation of C2+ products. This work provides new insights into the design of hydrophobic CO2 reduction electrocatalysts for the preparation of C2+ products.

Developing Isomeric Peptides for Mimicking the Sequence-Activity Landscapes of Enzyme Evolution.

Enzymes catalyze almost all material conversion processes within living organisms, yet their natural evolution remains unobserved. Short peptides, derived from proteins and featuring active sites, have emerged as promising building blocks for constructing bioactive supramolecular materials that mimic native proteins through self-assembly. Herein, we employ histidine-containing isomeric tetrapeptides KHFF, HKFF, KFHF, HFKF, FKHF, and FHKF to craft supramolecular self-assemblies, aiming to explore the sequence-activity landscapes of enzyme evolution. Our investigations reveal the profound impact of peptide sequence variations on both assembly behavior and catalytic activity as hydrolytic simulation enzymes. During self-assembly, a delicate balance of multiple intermolecular interactions, particularly hydrogen bonding and aromatic-aromatic interactions, influences nanostructure formation, yielding various morphologies (e.g., nanofibers, nanospheres, and nanodiscs). Furthermore, the analysis of the structure-activity relationship demonstrates a strong correlation between the distribution of the His active site on the nanostructures and the formation of the catalytic microenvironment. This investigation of the sequence-structure-activity paradigm reflects how natural enzymes enhance catalytic activity by adjusting the primary structure during evolution, promoting fundamental research related to enzyme evolutionary processes.

Bioinspired bimetallic metal–organic framework nanozyme with laccase-mimicking activity for detection and removal of phenolic contaminants

Laccase, despite its eco-friendly nature, faces constraints due to cost and inherent vulnerability, restricting its widespread application. Therefore, pursuing the development of a robust laccase mimetic displaying exceptional activity remains an ongoing endeavor. This research synthesized a bimetallic metal–organic framework nanozyme (Cu-Mn MOF) with enhanced laccase-mimicking activity via a one-step solvothermal method. The diverse Cu redox valence state of the nanozyme mimics the multi-copper active center of laccase, which endows Cu-Mn MOF with laccase-mimicking activity. Incorporating Mn introduces a novel metal center into the MOF, creating a catalytic microenvironment. Bimetallic Cu-Mn synergistic interplay accelerates the electron transfer rate, resulting in enhanced laccase-mimicking activity. The Michaelis constant of Cu-Mn MOF for 2,4-dichlorophenol (2,4-DP) registers at 0.080 mM, displaying remarkable stability and recyclability even under stringent conditions, thereby achieving a comprehensive surpass of laccase. Accordingly, Cu-Mn MOF was utilized to degrade phenolic compounds and design a smartphone sensing platform to facilitate portable and visual detection of phenol. Utilizing the occurrence of Cu-S coordination, which accelerates the electron transfer rate, a thiourea-enhanced Cu-Mn MOF was designed to improve the degradation rate. The limit of detection (LOD) for smartphone platform is 0.159 μM, with a linear detection range of 1–40 μM. The detection method was applied to determine the phenol in spiked samples with the spiked recoveries rate of 96.05–104.30 % and the relative standard deviations less than ± 4 %. The outcomes of these applications reveal the vast application potential of Cu-Mn MOF in environmental engineering.

Role of H2O in Catalytic Conversion of C1 Molecules.

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.

A Self-Adaptive Pyroptosis Inducer: Optimizing the Catalytic Microenvironment of Nanozymes by Membrane-Adhered Microbe Enables Potent Cancer Immunotherapy.

Pyroptosis has garnered increasing attention in cancer immunotherapy. Moreover, increasing plasma membrane damage by reactive oxygen species (ROS) is considered an effective strategy for promoting pyroptosis. However, the current tactics for enhancing membrane rupture in pyroptosis are limited by the inherent drawbacks of ROS and the immunosuppressive tumor microenvironment. Herein, a self-adaptive pyroptosis inducer (LPZ) is designed by integrating Lactobacillus rhamnosus GG (LGG) and an enzyme-like metal-organic framework to achieve potent pyroptosis immunotherapy. LPZ can adhere to cancer cell membranes through the interaction between the pili of LGG and the mucin of cancer cells. In particular, the adaptive formula can gradually enhance the ability of nanozymes to produce ROS by creating an acidic microenvironment through anaerobic respiration. These results verify that LPZ could generate high levels of ROS both on the membrane and within cancer cells, leading to pyroptotic cell death and strong antitumor immunity. Meanwhile, LGG are eventually killed by ROS in this process to halt their respiration and prevent potential biosafety concerns. Overall, this work provides new inspiration for the design of self-adaptive nanocatalytic drugs for cancer immunotherapy.

Efficient bionic nanozyme based on AuPt NPs@ZIF-90 used for cyclic catalysis multimodal tumor therapy.

Multimodal therapy based on nanozyme is expected to become a novel option for tumor treatment. However, the catalytic efficiency of nanozymes and the hypoxia microenvironment of tumors limit the therapeutic effect of nanozymes. Herein, we screened a small molecule of midazole-2-carboxaldehyde (ICA) to prepare ZIF-90 and embedded gold and platinum nanoparticles to obtain ZAAP. ZAAP possessed a multi-enzymatic cascade of catalytic processes including greatly enhanced peroxidase activity via a "bionic" catalytic microenvironment (enhanced 23-fold), catalase and glucose oxidase activities, resulting in glucose decomposition to continuously supply H2O2, peroxidases for the catabolism of H2O2 to generate ROS and peroxidase-induced oxygen generation for continuous oxidation of glucose. All the above processes built a catalysis cycle that greatly promotes the generation of ROS and oxygen as well as the consumption of glucose, leading to the chemical dynamic therapy function and alleviating tumor hypoxia. In addition to the photothermal effect of ZAAP, a synergistic treatment of chemical dynamic/photothermal/starvation therapy was achieved, and the tumor inhibition rate reached 96.4% within 2 weeks, indicating that ZAAP shows great potential in nanozyme-based synergistic multimodal tumor treatment.

Facile preparation of high-efficiency peroxidase mimics: modulation of the catalytic microenvironment of LDH nanozymes through defect engineering induced by amino acid intercalation.

Nanozymes have gained much attention as a replacement for natural enzymes duo to their unique advantages. Two-dimensional layered double hydroxide (LDH) nanomaterials with high physicochemical plasticity are emerging as the main forces for the construction of nanozymes. Unfortunately, high-performance LDH nanozymes are still scarce. Recently, defects in nanomaterials have been verified to play a significant role in modulating the catalytic microenvironment, thereby improving catalytic performances of nanozymes. Therefore, the marriage between defect engineering and LDH nanozymes is expected to spark new possibilities. In this work, twenty kinds of natural amino acids were separately inserted into the interlayer of CoFe-LDH to obtain defect-rich CoFe-LDH nanozymes. The peroxidase (POD)-like activity and catalytic mechanism of the as-prepared LDH nanozymes were systematically studied. The results showed that the intercalation of amino acids can effectively enhance the POD-like activity of LDH nanozymes owing to the increasing oxygen/metal vacancies. And l-cysteine intercalated LDH exhibited the highest catalytic activity ascribed to its thiol group. As a proof of concept, LDH nanozymes with superb POD-like activity were used in biosensing and antibacterial applications. This work suggests that modulating the catalytic microenvironment through defect engineering is an effective way to obtain high-efficiency POD mimics.

Porous reticular Co@Fe metal-organic gel: dual-function simulated peroxidase nanozyme for both colorimetric sensing and antibacterial applications.

Constructing metal-organic gels (MOGs) with enzyme-catalyzed activity and studying their catalytic mechanism are crucial for the development of novel nanozyme materials. In this study, a Co@Fe MOG with excellent peroxidase activity was developed by a simple and mild one-pot process. The results showed that the material exhibited almost a single peroxidase activity under optimal pH conditions, which allowed it to attract and oxidize the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). Based on the active electron transfer between the metal centers and the organic ligand in the synthetic material, the Co@Fe MOG-H2O2-TMB system was verified to be able to detect H2O2 and citric acid (CA). The catalytic microenvironment formed by the adsorption and the catalytic center accelerated the electron-transfer rate, which expedited the generation of hydroxyl radicals (˙OH, a kind of reactive oxygen species (ROS)) in the presence of H2O2. The persistence and high intensity of ˙OH generation were proven, which would endow Co@Fe MOG with a certain antibacterial ability, promoting the healing of bacteria-infected wounds. In conclusion, this study contributes to the development efforts toward the application systems of nanozymes for marker detection and antibacterial activity.

(Invited) The Liquid Sunlight Alliance: Solar-to-Chemical Energy Using Systems of Catalytic Microenvironments

The Liquid Sunlight Alliance’s science program is focused on codesigning systems that convert CO2 into useful fuels with high efficiency, selectivity and durability using sunlight as its sole source of energy. The function of the (photo)electrocatalytic reaction center is inextricably tied to the center’s connections to its surroundings, which govern the availability of reactants and charge carriers, and the removal of desired products. The intrinsic scale of these connections defines the catalytic microenvironment. This talk will describe our current understanding of key aspects of this microenvironment, with a specific focus on how both the catalyst nanostructure and the presence of liquid and solid electrolytes control the availability of dissolved anions, cations, water and CO2.

A Dual-Functional MXene-Based Bioanode for Wearable Self-Charging Biosupercapacitors.

As a reliable energy-supply platform for wearable electronics, biosupercapacitors combine the characteristics of biofuel cells and supercapacitors to harvest and store the energy from human's sweat. However, the bulky preparation process and deep embedding of enzyme active sites in bioelectrodes usually limit the energy-harvesting process, retarding the practical power-supply sceneries especially during the complicated in vivo motion. Herein, a MXene/single-walled carbon nanotube/lactate oxidase hierarchical structure as the dual-functional bioanode is designed, which can not only provide a superior 3D catalytic microenvironment for enzyme accommodation to harvest energy from sweat, but also offers sufficient capacitance to store energy via the electrical double-layer capacitor. A wearable biosupercapacitor is fabricated in the "island-bridge" structure with a composite bioanode, active carbon/Pt cathode, polyacrylamide hydrogel substrate, and liquid metal conductor. The device exhibits an open-circuit voltageof 0.48V and the high power density of 220.9 µW cm-2 at 0.5mA cm-2 . The compact conformal adhesion with skin is successfully maintained under stretching/bending conditions. After repeatedly stretching the devices, there is no significant power attenuation in pulsed output. The unique bioelectrode structure and attractive energy harvesting/storing properties demonstrate the promising potential of this biosupercapacitor as a micro self-powered platform of wearable electronics.

Catalytic microenvironment regulation by introducing biochar into MIL-101Fe derivative for enhanced persulfate activation: Efficient antibiotic removal and RSM optimization

Persulfate-based advanced oxidization process was widely investigated in antibiotic removal. MOFs-derived carbon was potential in activating persulfate, while the inevitable sintering and agglomeration effect of catalysts during carbonization resulted in reduced performance. Low-cost biochar was a desired carrier in designing functional composites. Herein, MIL-101Fe-derived carbon/biochar composites (MCB-900) were prepared via carbonizing MIL-101Fe/corn stalk composites. Biochar supporting achieved the dispersion of MIL-101Fe derivative avoiding the agglomeration effect, but also regulated the catalytic microenvironment with more accessible active sites, high porosity, and structural defects. Accordingly, MCB-900 exhibited more efficient norfloxacin (NOF) removal (96.44 %) than biochar (32.90 %) or MIL-101Fe-derived carbon (79.49 %) via exciting PDS by the transformation of Fe species and carbonyl groups. It was found that NOF degradation was ascribed to radical and non-radical oxidization (SO4•-, O2•-, and 1O2), involving two possible degradation pathways according to LC-MS. MCB-900/PDS system exhibited high anti-interference capability for pH (2–10) and anions (Cl-, HCO3–, H2PO4-), and was suitable for actual water matrixes and various organic pollutants removal. Further, with optimization by RSM, low dosages of PDS and MCB-900 could also reach high NOF removal (>95 %). Combining emerging MOFs with traditional biochar, this work provided an effective means and reference to design high-efficiency catalysts for antibiotic removal in water treatment.

Grafting amine-functionalized ligand layer on catalyst for electrochemical CO2 capture and utilization

Direct electrochemical CO2 capture and utilization from flue gas offers appealing route to closing the carbon cycle and avoiding the cost for CO2 purification. Yet, the low CO2 concentration in flue gas and competing oxygen reduction reaction (ORR) pose severe challenges for this process. Herein, we report 4-aminobutylphosphonic acid ligand layer capped Ag nanoparticles (NH2BPA-Ag) for high-efficiency conversion of simulated flue gas (SFG). The amino group in NH2BPA is available for CO2 capture and activation, while phosphonic acid groups inhibit ORR by desorbing *OOH intermediate. NH2BPA-Ag achieves 82% CO Faradaic efficiency (FECO) in H-cell for SFG reduction and enhances FECO 2.6 times over pristine Ag nanoparticles. In a membrane electrode assembly electrolyzer, NH2BPA-Ag shows 79.6% FECO and 38.1% full-cell energy efficiency at 48 mA cm-2 for SFG conversion. This study highlights the strategy of tailoring catalytic microenvironments at molecular level for realizing a highly selective performance.

Next Generation Noble Metal‐Engineered Catalysts: From Structure Evolution to Structure‐Reactivity Correlation in Water Splitting

AbstractNoble metal‐engineered catalysts (NMECs) play an important role in promoting the practical utilization of water‐splitting devices in hydrogen energy systems. While owing to the complicated catalytic centers, diverse support structures, and changing microenvironments, NMECs still face many challenges when it comes to designing and analyzing the precise catalytic sites and activity‐mechanism analyses, which are crucial for their future developments. Here, this cutting‐edge review systematically discusses recent advancements in designing NMECs for water electrolysis, including the structure evolution, microenvironment modulation, structure‐reactivity correlation, and new horizons. First, the fundamental advantages, mechanisms, and evaluation methods of NMECs for water splitting are outlined. Then, the strategies to modulate the catalytic microenvironments of NMECs are thoroughly summarized, such as crystal phase modulation, alloying effects, crystallization degrees, size effects, and substrate effects. In particular, there are valuable perspectives on bond interactions, theoretical calculations, and evaluation methods to disclose the catalytic mechanisms. Thereafter, a special emphasis is given on structure‐reactivity correlation, performances, and water‐splitting devices. Finally, a thorough discussion of the upcoming difficulties and new directions for developing next‐generation NMECs is presented. It is believed that the review will have a significant influence on creating noble metal‐based catalysts in the field of electrolytic water‐splitting.