Metal bond strength regulation enables large-scale synthesis of intermetallic nanocrystals for practical fuel cells.

Structurally ordered L10-PtM (M = Fe, Co, Ni and so on) intermetallic nanocrystals, benefiting from the chemically ordered structure and higher stability, are one of the best electrocatalysts used for fuel cells. However, their practical development is greatly plagued by the challenge that the high-temperature (>600 °C) annealing treatment necessary for realizing the ordered structure usually leads to severe particle sintering, morphology change and low ordering degree, which makes it very difficult for the gram-scale preparation of desirable PtM intermetallic nanocrystals with high Pt content for practical fuel cell applications. Here we report a new concept involving the low-melting-point-metal (M' = Sn, Ga, In)-induced bond strength weakening strategy to reduce Ea and promote the ordering process of PtM (M = Ni, Co, Fe, Cu and Zn) alloy catalysts for a higher ordering degree. We demonstrate that the introduction of M' can reduce the ordering temperature to extremely low temperatures (≤450 °C) and thus enable the preparation of high-Pt-content (≥40 wt%) L10-Pt-M-M' intermetallic nanocrystals as well as ten-gram-scale production. X-ray spectroscopy studies, in situ electron microscopy and theoretical calculations reveal the fundamental mechanism of the Sn-facilitated ordering process at low temperatures, which involves weakened bond strength and consequently reduced Ea via Sn doping, the formation and fast diffusion of low-coordinated surface free atoms, and subsequent L10 nucleation. The developed L10-Ga-PtNi/C catalysts display outstanding performance in H2-air fuel cells under both light- and heavy-duty vehicle conditions. Under the latter condition, the 40% L10-Pt50Ni35Ga15/C catalyst delivers a high current density of 1.67 A cm-2 at 0.7 V and retains 80% of the current density after extended 90,000 cycles, which exceeds the United States Department of Energy performance metrics and represents among the best cathodic electrocatalysts for practical proton-exchange membrane fuel cells.

Constructing Gradient Orbital Coupling to Induce Reactive Metal-Support Interaction in Pt-Carbide Electrocatalysts for Efficient Methanol Oxidation.

Reactive metal-support interaction (RMSI) is an emerging way to regulate the catalytic performance for supported metal catalysts. However, the induction of RMSI by the thermal reduction is often accompanied by the encapsulation effect on metals, which limits the mechanism research and applications of RMSI. In this work, a gradient orbital coupling construction strategy was successfully developed to induce RMSI in Pt-carbide system without a reductant, leading to the formation of L12-PtxM-MCy (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) intermetallic electrocatalysts. Density functional theory (DFT) calculations suggest that the gradient coupling of the d(M)-2p(C)-5d(Pt) orbital would induce the electron transfer from M to C covalent bonds to Pt NPs, which facilitates the formation of C vacancy (Cv) and the subsequent M migration (occurrence of RMSI). Moreover, the good correlation between the formation energy of Cv and the onset temperature of RMSI in Pt-MCx systems proves the key role of nonmetallic atomic vacancy formation for inducing RMSI. The developed L12-Pt3Ti-TiC catalyst exhibits excellent acidic methanol oxidation reaction activity, with mass activity of 2.36 A mgPt-1 in half-cell and a peak power density of 187.9 mW mgPt-1 in a direct methanol fuel cell, which is one of the best catalysts ever reported. DFT calculations reveal that L12-Pt3Ti-TiC favorably weakens *CO absorption compared to Pt-TiC due to the change of the absorption site from Pt to Ti, which accounts for the enhanced MOR performance.

Introducing Electron Buffers into Intermetallic Pt Alloys against Surface Polarization for High-Performing Fuel Cells.

Surface polarization under harsh electrochemical environments usually puts catalysts in a thermodynamically unstable state, which strictly hampers the thermodynamic stability of Pt-based catalysts in high-performance fuel cells. Here, we report a strategy by introducing electron buffers (variable-valence metals, M = Ti, V, Cr, and Nb) into intermetallic Pt alloy nanoparticle catalysts to suppress the surface polarization of Pt shells using the structurally ordered L10-M-PtFe as a proof of concept. Operando X-ray absorption spectra analysis suggests that with the potential increase, electron buffers, especially Cr, could facilitate an electron flow to form a electron-enriched Pt shell and thus weaken the surface polarization and tensile Pt strain. The best-performing L10-Cr-PtFe/C catalyst delivers superb oxygen reduction reaction (ORR) activity (mass activity = 1.41/1.02 A mgPt-1 at 0.9 V, rated power density = 14.0/9.2 W mgPt-1 in H2-air under a total Pt loading of 0.075/0.125 mgPt cm-2, respectively) and stability (20 mV voltage loss at 0.8 A cm-2 after 60,000 cycles of accelerated durability test) in a fuel cell cathode, representing one of the best reported ORR catalysts. Density functional theory calculations reveal that the optimized surface strain by introducing Cr on L10-PtFe/C accounts for the enhanced ORR activity, and the durability enhancement stems from the charge transfer contribution of Cr to the Pt shells and the increased kinetic energy barrier for Pt dissolution/Fe diffusion.

Trace Selenium Doping for Improving the Reaction Kinetics of ZnS Cathode for Aqueous Zn-S Batteries.

Aqueous Zinc-sulfur (Zn-S) batteries are promising for the field of energy storage due to their low cost, high theoretical capacity, and safety. However, the large volume expansion and the inherently poor conductivity of sulfur would result in electrode cracking and sluggish reaction kinetics, limiting the practical application of Zn-S batteries. Herein, commercial zinc sulfide (ZnS) is employed instead of S as cathode and proposed a doping modification strategy to solve the above problems. The designed ZnS0.93Se0.07 cathode shows good cycle stability and much-improved reaction kinetics, which is due to the smaller bandgap of ZnS0.93Se0.07 (1.40 eV) compared to ZnS (1.86 eV). As a result, the obtained ZnS0.93Se0.07 cathode exhibits a high specific capacity of 552 mAh g-1 (1672.6 mAh g-1 based on S) at 0.1 A g-1 and 330 mAh g-1 (1000 mAh g-1 based on S) at 2 A g-1. Moreover, the ZnS0.93Se0.07 cathode can provide a high areal capacity of 3.8 mAh cm-2 at a high mass loading of 10 mg cm-2 and limited electrolyte (4 µL mg-1). This work provides a simple and effective cathode modification strategy, which is conducive to promoting the practical application of Zn-S batteries.

In Operando Monitoring the Stress Evolution of Silicon Anode Electrodes during Battery Operation via Optical Fiber Sensors.

Silicon (Si) anode has attracted broad attention because of its high theoretical specific capacity and low working potential. However, the severe volumetric changes of Si particles during the lithiation process cause expansion and contraction of the electrodes, which induces a repeatedly repair of solid electrolyte interphase, resulting in an excessive consuming of electrolyte and rapid capacity decay. Clearly known the deformation and stress changing at µÎµ resolution in the Si-based electrode during battery operation provides invaluable information for the battery research and development. Here, an in operando approach is developed to monitor the stress evolution of Si anode electrodes via optical fiber Bragg grating (FBG) sensors. By implanting FBG sensor at specific locations in the pouch cells with different Si anodes, the stress evolution of Si electrodes has been systematically investigated, and Δσ/areal capacity is proposed for stress assessment. The results indicate that the differences in stress evolution are nested in the morphological changes of Si particles and the evolution characteristics of electrode structures. The proposed technique provides a brand-new view for understanding the electrochemical mechanics of Si electrodes during battery operation.

Engineering Li Metal Anode for Garnet-Based Solid-State Batteries.

ConspectusThe past 30 years have witnessed the great achievements of Li-ion batteries (LIBs) based on a graphite anode and liquid organic electrolytes. Yet the limited energy density of a graphite anode and unavoidable safety risks caused by flammable liquid organic electrolytes hinder further developments of LIBs. To reach higher energy density, Li metal anodes (LMAs) with high capacity and low electrode potential are a promising choice. However, LMAs suffer from more serious safety concerns than the graphite anode in liquid LIBs. The dilemma of safety and energy density remains an inevitable obstacle in the way of LIBs.Solid-state batteries (SSBs) offer new opportunities to simultaneously achieve intrinsic safety and high energy density. Among all types of SSBs that are based on oxides, polymers, sulfides, or halides, garnet-type SSBs seem to be one of the most attractive choices due to garnet's merits in high ionic conductivities (10-4-10-3 S/cm at room temperature), wide electrochemical windows (0-6 V), and intrinsically high safety. However, garnet-type SSBs are faced with large interfacial impedance and short-circuit problems caused by Li dendrites. Recently, engineered Li metal anodes (ELMAs) have shown unique advantages in tackling interface issues and attracted extensive research interest.In this Account, we focus on fundamental understandings and provide an in-depth review of ELMAs in garnet-based SSBs. Considering the limited space, we mainly discuss the recent progress made in our groups. First, we introduce the design guidelines for ELMAs and emphasize the unique role of theoretical calculation in predicting and optimizing ELMAs. Then we discuss the interface compatibility of ELMAs with garnet SSEs in details. Specifically, we have demonstrated the advantages of ELMAs in enhancing interface contact and suppressing Li dendrite growth. Next, we attentively analyze the gaps between laboratory and practical applications. We strongly recommend establishing a unified testing standard, with a practically desired areal capacity per cycle (>3.0 mAh/cm2) and a precisely controlled Li capacity excess. Finally, novel chances to enhance ELMAs' processability and fabricate thin Li foils are highlighted. We believe that this Account will offer an insightful analysis of ELMAs' recent advancements and push forward their practical applications.

Less is more: a perspective on thinning lithium metal towards high-energy-density rechargeable lithium batteries.

Lithium (Li) metal, owing to its high specific capacity and low redox potential as a Li+ ion source in rechargeable lithium batteries, shows impressive prospects for electrochemical energy storage. However, engineering Li metal into thin foils has historically remained difficult, owing to its stickiness and fragility upon mechanical rolling. Consequently, using thick Li in battery systems betrays the original target for achieving higher energy density, results in material waste, and creates illusions on evaluating modification strategies for taming the highly reactive Li metal anode. Being apprehensive of this, in the tutorial review, we illustrate the argument of applying thin Li (<50 µm, preferably ≤30 µm) to achieve more realistic and advanced battery systems. A brief overview of Li is sketched first to help understand its role in batteries. Then, the reasons for pursuing thin Li are critically analyzed. Next, seminal technologies enabling the fabrication of thin Li are summarized and compared, which calls for the participation of experts from mechanical engineering, metallurgy, electrochemistry, and other fields. Subsequently, the possible applications of thin Li in batteries are presented. With the deployment of thin Li, there are new challenges and opportunities to encounter and an outlook is afforded thereof. Holy-grail Li metal anodes, combined with the subtraction operation in thickness and compatible modification strategies, would bring about a truly great leap forward in electrochemical energy storage.

Tailoring Zirconia Supported Intermetallic Platinum Alloy via Reactive Metal-Support Interactions for High-Performing Fuel Cells.

Developing efficient and anti-corrosive oxygen reduction reaction (ORR) catalysts is of great importance for the applications of proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel approach to prepare metal oxides supported intermetallic Pt alloy nanoparticles (NPs) via the reactive metal-support interaction (RMSI) as ORR catalysts, using Ni-doped cubic ZrO2 (Ni/ZrO2) supported L10-PtNi NPs as a proof of concept. Benefiting from the Ni migration during RMSI, the oxygen vacancy concentrations in the support are increased, leading to an electron enrichment of Pt. The optimal L10-PtNi-Ni/ZrO2-RMSI catalyst achieves remarkably low mass activity (MA) loss (17.8 %) after 400,000 accelerated durability test cycles in a half-cell and exceptional PEMFC performance (MA=0.76 A mgPt -1 at 0.9 V, peak power density=1.52/0.92 W cm-2 in H2-O2/-air, and 18.4 % MA decay after 30,000 cycles), representing the best reported Pt-based ORR catalysts without carbon supports. Density functional theory (DFT) calculations reveal that L10-PtNi-Ni/ZrO2-RMSI requires a lower energetic barrier for ORR than L10-PtNi-Ni/ZrO2 (direct loading), which is ascribed to a decreased Bader charge transfer between Pt and *OH, and the improved stability of L10-PtNi-Ni/ZrO2-RMSI compared to L10-PtNi-C can be contributed to the increased adhesion energy and Ni vacancy formation energy within the PtNi alloy.

Enhancing the Initial Coulombic Efficiency of Sodium-Ion Batteries via Highly Active Na2 S as Presodiation Additive.

Recently, sodium-ion batteries (SIBs) have received considerable attention for large-scale energy storage applications. However, the low initial Coulombic efficiency of traditional SIBs severely impedes their further development. Here, a highly active Na2 S-based composite is employed as a self-sacrificial additive for sodium compensation in SIBs. The in situ synthesized Na2 S is wrapped in a carbon matrix with nanoscale particle size and good electrical conductivity, which helps it to achieve a significantly enhanced electrochemical activity as compare to commercial Na2 S. As a highly efficient presodiation additive, the proposed Na2 S/C composite can reach an initial charge capacity of 407 mAh g-1 . When 10 wt.% Na2 S/C additive is dispersed in the Na3 V2 (PO4 )3 cathode, and combined with a hard carbon anode, the full cell achieves 24.3% higher first discharge capacity, which corresponds to a 18.3% increase in the energy density from 117.2 to 138.6 Wh kg-1 . Meanwhile, it is found that the Na2 S additive does not generate additional gas during the initial charging process, and under an appropriate content, its reaction product has no adverse impact on the cycling stability and rate performance of SIBs. Overall, this work establishes Na2 S as a highly effective additive for the construction of advanced high-energy-density SIBs.

Insights into Reversible Sodium Intercalation in a Novel Sodium-Deficient NASICON-Type Structure:Na3.40 □0.60 Co0.5 Fe0.5 V(PO4 )3.

The rational design of novel high-performance cathode materials for sodium-ion batteries is a challenge for the development of the renewable energy sector. Here, a new sodium-deficient NASICON phosphate, namely Na3.40 □0.60 Co0.5 Fe0.5 V(PO4 )3 , demonstrating the excellent electrochemical performance is reported. The presence of Co allows a third Na+ to participate in the reaction thus exhibiting a high reversible capacity of ≈155 mAh g-1 in the voltage range of 2.0-4.0 V versus Na+ /Na with a reversible single-phase mechanism and a small volume shrinkage of ≈5.97% at 4.0 V. 23 Na solid-state nuclear magnetic resonance (NMR) combined with ex situ X-ray diffraction (XRD) refinements provide evidence for a preferential Na+ insertion within the Na2 site. Furthermore, the enhanced sodium kinetics ascribed to Co-substitution is also confirmed in combination with electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT), and theoretical calculation.

Decoupling of the anode and cathode ultrasonic responses to the state of charge of a lithium-ion battery.

An ultrasonic method for lithium-ion battery (LIB) state of charge (SoC) estimation is a promising emerging technology which may largely improve the SoC estimation accuracy. Previously, it was unknown whether the SoC change induced ultrasonic signal change originated from the anode or the cathode, because the thicknesses of cathodes, anodes and separators are much smaller than the ultrasonic wavelength, which makes it impossible to decouple the anodic and cathodic influence. To quantitatively solve the above problem, we have designed a special half-cell architecture with an extra-thick separator (675 µm) to study the reflected ultrasonic signal. The thickened separator would significantly delay the reflection of ultrasonic waves from the counter-electrode (Li), so that the influence of the working electrode (LiFePO4 or graphite) on the ultrasonic wave can be studied separately. As a result, in the Gr anode, the time of flight (ToF) of the ultrasonic wave decreases with SoC, the changing rate coefficient of which is in the range of -110 to -70 ps µmGr thickness-1, depending on the compact density. A lower compact density electrode leads to a more significant ultrasonic ToF decrease and intensity increase while in the LFP cathode, the ToF increases with SoC, the changing rate coefficient of which is in the range of 15-43 ps µmLFP thickness-1. The ToF change of the transmitted ultrasound through multilayered LIB matches very well with the sum of the ToF change in each electrode measured with our half-cells.

How Mortality Salience and Self-Construal Make a Difference: An Online Experiment to Test Perception of Importance of COVID-19 Vaccines in China.

To better understand why Chinese residents' COVID-19 perceptions of the importance of vaccination change dramatically over time, this research used an online lab-like experiment to test the antecedents of individuals' perception of the importance of COVID-19 vaccines. We find that participants who view themselves as separate from others (i.e. independent self-construal) perceive COVID-19 vaccines as more important than Hepatitis B vaccines (i.e. control group), regardless of how salient mortality is for them. In contrast, among participants who view themselves as a part of their social groups (i.e. interdependent self-construal), awareness of death (i.e. mortality salience) plays a moderating role. Specifically, when mortality is salient, COVID-19 vaccines are considered more important than Hepatitis B vaccines; when morality is not salient, vaccine type does not make a difference on perceptions of vaccine importance.

Inducing Covalent Atomic Interaction in Intermetallic Pt Alloy Nanocatalysts for High-Performance Fuel Cells.

The harsh working environments of proton exchange membrane fuel cells (PEMFCs) pose huge challenges to the stability of Pt-based alloy catalysts. The widespread presence of metallic bonds with significantly delocalized electron distribution often lead to component segregation and rapid performance decay. Here we report L10 -Pt2 CuGa intermetallic nanoparticles with a unique covalent atomic interaction between Pt-Ga as high-performance PEMFC cathode catalysts. The L10 -Pt2 CuGa/C catalyst shows superb oxygen reduction reaction (ORR) activity and stability in fuel cell cathode (mass activity=0.57 A mgPt -1 at 0.9 V, peak power density=2.60/1.24 W cm-2 in H2 -O2 /air, 28 mV voltage loss at 0.8 A cm-2 after 30 000 cycles). Theoretical calculations reveal the optimized adsorption of oxygen intermediates via the formed biaxial strain on L10 -Pt2 CuGa surface, and the durability enhancement stems from the stronger Pt-M bonds than those in L11 -PtCu resulted from Pt-Ga covalent interactions.

Electrochemical Reactivation of Dead Li2 S for Li-S Batteries in Non-Solvating Electrolytes.

The use of non-solvating, or as-called sparingly-solvating, electrolytes (NSEs), is regarded as one of the most promising solutions to the obstacles to the practical applications of Li-S batteries. However, it remains a puzzle that long-life Li-S batteries have rarely, if not never, been reported with NSEs, despite their good compatibility with Li anode. Here, we find the capacity decay of Li-S batteries in NSEs is mainly due to the accumulation of the dead Li2 S at the cathode side, rather than the degradation of the anodes or electrolytes. Based on this understanding, we propose an electrochemical strategy to reactivate the accumulated Li2 S and revive the dead Li-S batteries in NSEs. With such a facile approach, Li-S batteries with significantly improved cycling stability and accelerated dynamics are achieved with diglyme-, acetonitrile- and 1,2-dimethoxyethane-based NSEs. Our finding may rebuild the confidence in exploiting non-solvating Li-S batteries with practical competitiveness.

Solid/Quasi-Solid Phase Conversion of Sulfur in Lithium-Sulfur Battery.

The lithium-sulfur (Li-S) battery is considered as one of the most promising options because the redox couple has almost the highest theoretical specific energy (2600 Wh kg-1 ) among all solid anode-cathode candidates for rechargeable batteries. The "solid-liquid-solid" mechanism has become a dominating phase transformation process since it was first reported, although this cathode mode suffers from a tough "shuttle" phenomenon due to the dissolution of the soluble intermediate polysulfides generated during the charging-discharging process, which causes rapid loss of energy-bearing material and shortened lifespan. For decades, tremendous efforts have been made to restrict the shuttle effect. Changing sulfur conversion to "solid-solid" mode or "quasi-solid" mode, which successfully exceed the limit of the dissolution of the intermediates, and may address the root of the problem. In this review, the main focus is on the fundamental chemistry of the "solid-solid" and "quasi-solid" phase transformation of the sulfur cathode. First, the strategies of sulfur immobilization in "solid-liquid-solid" multi-phase conversions as well as the pivotal influence factors for the electrochemical conversion process are briefly introduced. Then, the different routes are summarized to realize the "solid-solid" and "quasi-solid" redox mechanisms. Finally, a perspectives on building high-energy-density Li-S batteries are provided.

In Situ Constructing Coordination Compounds Interphase to Stabilize Zn Metal Anode for High-Performance Aqueous Zn-SeS2 Batteries.

Aqueous zinc (Zn) metal batteries have been regarded as the most promising aqueous batteries due to their low redox potential, high theoretical capacity, and abundant Zn resources. Unfortunately, Zn dendrite growth and serious side reactions drastically curtail the cycle life, severely affecting their large-scale application. Herein, a multifunctional ordered Zn-aminotrimethylene phosphonic acid (Zn-ATMP) film is in situ modified on the surface of metal Zn via a facile etching process. The modified layer can not only retard the side reactions and suppress the corrosion rate, but also lower the Zn nucleation overpotential and accelerate diffusion and homogenize deposition of Zn2+ due to the strong Zn affinity. Consequently, the as-prepared Zn-ATMP@Zn anode in the symmetric cell enables long-term lifespan (over 1000 h) at 10.0 mA cm-2 with a high areal capacity of 5 mAh cm-2 . Furthermore, when assembled with a SeS2 -based cathode, a long lifespan for over 280 cycles at 2 C can be achieved for the aqueous Zn-SeS2 battery. This work provides a reliable strategy for constructing stabilized Zn anode and accelerating the development of an aqueous energy storage system.

Fast Li-ion Conductor of Li3HoBr6 for Stable All-Solid-State Lithium-Sulfur Battery.

Rare-earth (RE) solid-state halide electrolytes have been extensively studied recently in the field of lithium (Li) ion all-solid-state batteries (ASSBs) due to their excellent electrochemical performances. Herein, a new RE-based solid halide electrolyte Li3HoBr6 (LHB) has been synthesized and exhibits high Li ion conductivity up to mS cm-1 at room temperature. Theoretical calculations have identified four different Li ion migration pathways, in which the out-of-plane pathways are much more favorable than the direct in-plane pathways. In addition, LHB has a wider electrochemical window in comparison to a sulfide solid electrolyte and good deformability. The LHB-based Li-sulfur ASSB assembled by cold pressing can exhibit good cycling stability with high Coulombic efficiency, which shows that LHB has potential application in ASSBs.

Thermally Aged Li-Mn-O Cathode with Stabilized Hybrid Cation and Anion Redox.

Though low-cost and environmentally friendly, Li-Mn-O cathodes suffer from low energy density. Although synthesized Li4Mn5O12-like overlithiated spinel cathode with reversible hybrid anion- and cation-redox (HACR) activities has a high initial capacity, it degrades rapidly due to oxygen loss and side-reaction-induced electrolyte decomposition. Herein, we develop a two-step heat treatment to promote local decomposition as Li4Mn5O12 → 2LiMn2O4 + Li2MnO3 + 1/2 O2↑, which releases near-surface reactive oxygen that is harmful to cycling stability. The produced nanocomposite delivers a high discharge capacity of 225 mAh/g and energy density of over 700 Wh/kg at active-material level at a current density of 100 mA/g between 1.8 to 4.7 V. Benefiting from suppressed oxygen loss and side reactions, 80% capacity retention is achieved after 214 cycles in half cells. With industrially acceptable electrolyte amount (6 g/Ah), full cells paired with Li4Ti5O12 anode have a good retention over 100 cycles.

High-Capacity and Long-Life Zinc Electrodeposition Enabled by a Self-Healable and Desolvation Shield for Aqueous Zinc-Ion Batteries.

Artificial interfaces can alleviate the side reactions and the formation of the metallic (e.g., Li, Na, and Zn) dendrites. However, the traditional ones always breakdown during the repeated plating/stripping and fail to regulate the electrodeposition behaviors of the electrodes. Herein, a self-healable ion regulator (SIR) is designed as a desolvation shield to protect the Zn electrodes and guide the Zn electrodeposition. Benefiting from the intermolecular hydrogen bonds, SIR shows a superb capability to in situ repair the plating/stripping-induced cracks. Besides, the results of theoretical calculations and electrochemical characterizations show that the coating reduces water molecules in the solvated sheath of hydrated Zn2+ and restrains the random Zn2+ diffusion on the Zn surface. Even with a coating layer of only 360 nm, the SIR-modified Zn electrode exhibits excellent long-term stability for >3500 h at 2 mAh cm-2 and >950 h at an ultrahigh areal capacity of 20 mAh cm-2 .

Rationally Designing Efficient Electrocatalysts for Direct Seawater Splitting: Challenges, Achievements, and Promises.

Directly splitting seawater to produce hydrogen provides a promising pathway for energy and environmental sustainability. However, current seawater splitting faces many challenges because of the sluggish kinetics, the presence of impurities, membrane contamination, and the competitive chloride oxidation reaction at the anode, which makes it more difficult than freshwater splitting. This Review firstly introduces the basic mechanisms of the anode and cathode reactions during seawater splitting. We critically analyze the primary principles for designing catalysts for seawater splitting in terms of both the hydrogen and oxygen evolution reactions, including with noble metal, noble metal free, and metal-free catalysts. Strategies to design effective catalysts, such as active site population, synergistic effect regulation, and surface engineering, are discussed. Furthermore, promises, perspectives, and challenges in developing seawater splitting technologies for clean hydrogen generation are summarized.