Direct Seawater Research Articles

CrOx Modified Nickel Phosphides Electrocatalyst for Stable Hydrogen Evolution Reaction in Neutral Media

AbstractThe development of efficient and long‐term stable electrodes for hydrogen evolution reaction (HER) in seawater is highly desirable for hydrogen generation but remains challenging. In this work, a highly active CrOx@Ni2P‐Ni5P4/NF electrode is developed and investigated its dynamic reconstruction for HER in neutral electrolytes. The combination of in situ Raman spectra and electrochemical measurements revealed the dynamic surface reconstruction of the catalyst during HER. The CrOx modification not only effectively facilitates water dissociation but also stabilizes the structure post‐reconstruction, enabling rapid and stable hydrogen generation in neutral media. Remarkably, CrOx@Ni2P‐Ni5P4/NF exhibits overpotentials of 109 and 263 mV at current densities of 10 and 100 mA cm−2 in 1 m PBS, respectively. Concurrently, it exhibits stable operation for 500 h in 1 m PBS and 140 h in natural seawater at current densities of 50 and 100 mA cm−2, respectively. The proposed catalytic electrode and the mechanistic insights present a significant stride toward the realization of metal phosphides for direct seawater splitting.

Geochemistry of cherts from the northern Jiangxi region, South China: Implication for paleoenvironment

The extensive bedded cherts deposited during the Ediacaran–Cambrian (E–C) transition period play a crucial role in understanding the geological evolution of this period, yet the origin of these cherts remains disputed. Here, we present new geochemical data for cherts of the Piyuancun (PYC) Formation deposited during the Late Ediacaran and the Hetang (HT) Formation deposited during the Early Cambrian in northern Jiangxi region, Lower Yangtze region, South China. The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments, while the HT cherts lack siliceous organism evidence. Major and trace element analysis, coupled with discriminant diagrams, indicate a possible shift in redox conditions of seawater during the E–C transition in the northern Jiangxi region. The shift suggests a change from weakly–moderately restricted euxinic conditions to strongly restricted euxinic conditions. Furthermore, the location of both cherts are distant from the source area of siliceous organisms. Fossil evidence, as well as the values of Fe/Ti and Fe/(Mn+Ti), Eu anomalies, Post-Archean Australian Shale (PAAS) normalized REE+Y patterns, and various discriminant diagrams, support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation, with the PYC cherts exhibiting weak hydrothermal evidence. Upwelling contributes to the formation of HT cherts and organic matter (OM) accumulation. Ocean acidification, triggered by OM degradation and biodegradation processes during the E–C transition period, leads to the extensive silica precipitation and preservation. These results enhance our understanding of the geological processes during the E–C transition.

Enabling direct seawater electrolysis by redox-inactive amphiphilic amines via chloride sequestration

Sustainable hydrogen production requires large amounts of treated freshwater and precious metals. Direct electrolysis of seawater without additional electrolytes can be a practical approach to address these limitations, however, it usually suffers from kinetically favored chlorine evolution reaction (CER), which is detrimental to an electrolysis system. We report that organocatalytic amphiphilic diamines play a crucial role in preventing the generation of chlorine gas. The feasibility of direct seawater electrolysis was demonstrated with pH-responsive organic amines, which can self-assemble under neutral and acidic conditions. Electrochemical analysis of our electrolysis in saline solutions revealed that (electro)chemical stability of amphiphilic diamines was responsible for preventing CER and hypochlorite formation. Our findings may have significant implications for the chemical industry and energy sectors as the world transitions towards renewable energy sources.

In-situ direct seawater electrolysis using floating platform in ocean with uncontrollable wave motion

Direct hydrogen production from inexhaustible seawater using abundant offshore wind power offers a promising pathway for achieving a sustainable energy industry and fuel economy. Various direct seawater electrolysis methods have been demonstrated to be effective at the laboratory scale. However, larger-scale in situ demonstrations that are completely free of corrosion and side reactions in fluctuating oceans are lacking. Here, fluctuating conditions of the ocean were considered for the first time, and seawater electrolysis in wave motion environment was achieved. We present the successful scaling of a floating seawater electrolysis system that employed wind power in Xinghua Bay and the integration of a 1.2 Nm3 h−1-scale pilot system. Stable electrolysis operation was achieved for over 240 h with an electrolytic energy consumption of 5 kWh Nm−3 H2 and a high purity (>99.9%) of hydrogen under fluctuating ocean conditions (0~0.9 m wave height, 0~15 m s−1 wind speed), which is comparable to that during onshore water electrolysis. The concentration of impurity ions in the electrolyte was low and stable over a long period of time under complex and changing scenarios. We identified the technological challenges and performances of the key system components and examined the future outlook for this emerging technology.

Recent Advances in High‐Performance Direct Seawater Electrolysis for “Green” Hydrogen

Electrocatalytic water splitting through the electrolyzer is the most promising strategy for hydrogen production. Recently, water electrolysis is mainly based on high‐purity freshwater, which not only consumes a large number of freshwater resources but also improves the overall cost due to the extra water purification system. Hence, direct electrolysis of seawater is more desirable for large‐scale hydrogen generation. As is known, the dominant rate‐determining step of overall water splitting is the anodic oxygen evolution reaction (OER), which involves four‐electron transfer and owns a much larger overpotential than cathodic hydrogen evolution reaction. The large challenge for the design of OER catalysts in the seawater media is the competition reaction between OER and chloride oxidation reaction, which greatly influences energy efficiency. Hence, except for the activity and stability, selectivity is another key point for seawater splitting. Herein, after a brief introduction of two half reactions for water splitting, the latest metal hydr(oxide) electrocatalysts with different crystalline structures are summarized according to the previous reports. Moreover, the advantages and disadvantages of three common water electrolyzers are compared. Finally, the perspectives of seawater electrolysis for hydrogen production are outlined for practical applications.

Is Direct Seawater Splitting Realistic with Conventional Electrolyzer Technologies?

Is Direct Seawater Splitting Realistic with Conventional Electrolyzer Technologies?

In Situ Phase Separation-Induced Self-Healing Catalyst for Efficient Direct Seawater Electrolysis.

Direct seawater electrolysis technology for sustainable hydrogen production has garnered significant attention, owing to its abundant resource supply and economic potential. However, the complex composition and high chloride concentration of seawater have hindered its practical implementation. In this study, we report an in situ-synthesized dual-phase electrocatalyst (HPS-NiMo), comprising an amorphous phosphide protective outer phase and a crystalline alloy inner phase with supplementary sulfur active sites, to improve the kinetics of direct seawater electrolysis. The HPS-NiMo exhibits long-term stability, remaining stable for periods exceeding 120 h at 200 mA cm-2; moreover, it lowers the required operating voltage to ∼1.8 V in natural seawater. The chlorine chemistry, corrosion during direct natural seawater electrolysis, and mechanism behind the high-performing catalysts are discussed. We also investigated the possibility of recovering the anode precipitates, which inevitably occurs during seawater electrolysis.

Unraveling the competition between the oxygen and chlorine evolution reactions in seawater electrolysis: Enhancing selectivity for green hydrogen production

Selective oxidation of water without production of chlorine during the electrolysis of seawater is a critical impediment towards obtaining green hydrogen. Indeed, understanding the complex competitive mechanisms of oxygen and chlorine formation at the anode is an analytic challenge. An argument for direct seawater electrolysis is presented with a dissection of the complications that arise at the anode in the presence of seawater ionic constituents such as the chloride ion. Electrolyser system durability and the impact on the current and voltage efficiencies are discussed. Critical challenges at the anode under the acidic conditions of proton exchange membrane water electrolysis interrelate the thermodynamic and kinetic constraints of the oxygen evolution reaction (OER) and the chlorine evolution reaction (CER) to elucidate the heterogenous mechanisms of the OER and the CER and the crucial stability predicament under selective OER electrocatalysis. The selectivity circumstances resolved by Density Functional Theory computations shed insight onto the reaction conditions that select for the preferred OER adsorbate chemisorption on the surface and substantiates the observed overpotentials required for the OER and CER; experimental rotating ring disk electrode analysis further indicate competitive adsorption of OER and CER reactants under an assumed Langmuir isotherm model. Identifying the rate determining step and breaking the scaling relationship of the AEM OER pathway may both improve the stability of the catalyst and achieve lower OER overpotentials. Critical insight is given into designing the heterogeneous electrocatalyst structure with selective facets, additional point defects, and augmented active site density through single atom catalysts. An argument for the utilization of ruthenium for its high natural ubiquity and modulable valence states that can facilitate atomic configurations with optimal active site d-band center energies to promote selective adsorbate binding is presented. Studies of in-situ filtration of the chloride ion under acidic conditions highlight the utility of manganese oxide and silica; the augmentation of the conductivity through manipulation of polaronic interactions; and the design of heterogeneous electrocatalysts with self-healing characteristics demonstrated in select molecular catalysts that may decrease the overpotential of the OER and achieve selectivity. It is with the hope that these design strategies provide insights into future research efforts to uncover an electrocatalytic surface selective for OER evolution under the perilous acidic conditions and reveal an effective solution as serendipitous as the abundancy of a natural resource such as seawater.

Coordination Engineering of Carbon Dots and Mn in Co-Based Phosphides for Highly Efficient Seawater Splitting at Ampere-Level Current Density.

Direct electrolysis of seawater to generate hydrogen is an attractive approach for storing renewable energy. However, direct seawater splitting suffers from low current density and limited operating stability, which severely hinders its industrialization. Herein, a promising strategy is reported to obtain a nano needle-like array catalyst-CDs-Mn-CoxP on nickel foam, in which the Mn─O─C bond tightly binds Mn, Carbon dots (CDs), and CoxP together. The coordination engineering of CDs and Mn not only effectively regulates the electronic structure of CoxP, but also endows the as-prepared catalyst with selectivity and marked long-term stability at ampere-level current density. Low overpotentials of 208 and 447mV are required to achieve 1000mA cm-2 for hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER) in simulated seawater, respectively. Cell potentials of 1.78 and 1.86V are needed to reach 500 and 1000mA cm-2 in alkaline seawater along with excellent durability for 350h. DFT studies have verified that the introduction of Mn and CDs effectively shifts the d-band center of Co-3d toward higher energy, thereby strengthening the adsorption of intermediates and enhancing the catalytic activity. This study sheds light on the development of highly effective and stable catalysts for large-scale seawater electrolysis.

Small Molecule Oxidation Facilitated Seawater Splitting for Hydrogen Production: Opportunities and Challenges

Direct seawater splitting is an environment‐friendly and promising technology to replace freshwater electrolysis for hydrogen production. The challenge of seawater electrolysis lies in the competition between chloride oxidation reaction (CER) and oxygen evolution reaction (OER), as well as electrode corrosion and poisoning caused by chloride. Some small molecules have lower anodic electrocatalytic oxidation potentials compared to OER and CER, making them possible to substitute OER and/or CER in coupled electrolyzers not only to eliminate the electrode corrosion problem but also to significantly enhance the energy efficiency of seawater electrolysis. This article reviews the progress of such small molecule oxidation facilitated seawater electrolyzer. Starting with an overview of the key challenges in seawater electrolysis, this review introduces the fundamentals and advantages of the coupled seawater electrolyzers and discusses the strategies for anodic small molecule oxidation and cathodic hydrogen evolution reaction, including utilizing Cl‐ as a reactive medium, value‐added chemical synthesis, pollutants electrooxidation, and optimizing electrolyzers. Finally, the challenges and prospects of small molecule oxidation facilitated seawater splitting are summarized, aiming to provide impetus for research and development on coupled seawater electrolysis technologies.

Solidophobic Surface for Electrochemical Extraction of High-Valued Mg(OH)2 Coupled with H2 Production from Seawater.

A significant challenge in direct seawater electrolysis is the rapid deactivation of the cathode due to the large scaling of Mg(OH)2. Herein, we synthesized a Pt-coated highly disordered NiCu alloy (Pt-NiCu alloy) electrode with superior solidophobic behavior, enabling stable hydrogen generation (100 mA cm-2, >1000 h durability) and simultaneous production of Mg(OH)2 (>99.0% purity) in electrolyte enriched with Mg2+ and Ca2+. The unconventional solidophobic property primarily stems from the high surface energy of the NiCu alloy substrate, which facilitates the adsorption of surface water and thereby compels the bulk formation of Mg(OH)2 via homogeneous nucleation. The discovery of this solidophobic electrode will revolutionarily simplify the existing techniques for seawater electrolysis and increase the economic viability for seawater electrolysis.

Optimized Transition Metal Phosphides for Direct Seawater Electrolysis: Current Trends.

Seawater electrolysis presents a viable route for sustainable large-scale hydrogen production, yet its practical application is hindered by several technical challenges. These include the sluggish kinetics of hydrogen evolution, poor stability, cation deposition at the cathode, electrode corrosion, and competing chloride oxidation at the anode. To overcome these obstacles, the development of innovative electrocatalysts is crucial. Transition metal phosphides (TMPs) have emerged as promising candidates owing to their superior catalytic performance and tunable structural properties. This review provides a comprehensive analysis of recent progress in the structural engineering of TMPs tailored for efficient seawater electrolysis. We delve into the catalytic mechanisms underpinning hydrogen and oxygen evolution reactions in different pH conditions, along with the detrimental side reactions that impede hydrogen production efficiency. Several methods to prepare TMPs are then introduced. Additionally, detailed discussions on structural modifications and interface engineering tactics are presented, showcasing strategies to enhance the activity and durability of TMP electrocatalysts. By analyzing current research findings, our review aims to inform ongoing research endeavors and foster advancements in seawater electrolysis for practical and ecologically sound hydrogen generation.

A Dual-Cation Exchange Membrane Electrolyzer for Continuous H2 Production from Seawater.

Direct seawater splitting (DSS) offers an aspirational route toward green hydrogen (H2) production but remains challenging when operating in a practically continuous manner, mainly due to the difficulty in establishing the water supply-consumption balance under the interference from impurity ions. A DSS system is reported for continuous ampere-level H2 production by coupling a dual-cation exchange membrane (CEM) three-compartment architecture with a circulatory electrolyte design. Monovalent-selective CEMs decouple the transmembrane water migration from interferences of Mg2+, Ca2+, and Cl- ions while maintaining ionic neutrality during electrolysis; the self-loop concentrated alkaline electrolyte ensures the constant gradient of water chemical potential, allowing a specific water supply-consumption balance relationship in a seawater-electrolyte-H2 sequence to be built among an expanded current range. Even paired with commercialized Ni foams, this electrolyzer (model size: 2 × 2 cm2) continuously produces H2 from flowing seawater with a rate of 7.5 mL min-1 at an industrially relevant current of 1.0 A over 100 h. More importantly, the energy consumption can be further reduced by coupling more efficient NiMo/NiFe foams (≈6.2 kWh Nm-3 H2 at 1.0 A), demonstrating the potential to further optimize the continuous DSS electrolyzer for practical applications.

Interface Engineering of Electrocatalysts for Efficient and Selective Oxygen Evolution in Alkaline/Seawater

Electrochemical water splitting is regarded as an effective technology for producing green hydrogen, which is crucial for addressing energy and environmental challenges. In particular, direct seawater splitting offers significant economic and environmental advantages. However, its efficiency is hindered by the high overpotential required for the oxygen evolution reaction (OER) and the competition from chloride oxidation. This review highlights the potential of interface engineering to overcome these limitations and develop efficient OER electrocatalysts. We comprehensively explore recent advancements in interface engineering for OER in both alkaline and seawater environments. We begin by introducing the mechanisms of freshwater and seawater electrolysis, emphasizing key considerations for OER catalyst design. Subsequently, we review the recent progress made in various interface engineering strategies, analyzing their impact on OER performance in both electrolytes. Finally, we outline promising future directions for developing efficient seawater oxidation catalysts through interface engineering.

Bipolar Membrane Seawater Splitting for Hydrogen Production: A Review.

The growing demand for clean energy has spurred the quest for sustainable alternatives to fossil fuels. Hydrogen has emerged as a promising candidate with its exceptional heating value and zero emissions upon combustion. However, conventional hydrogen production methods contribute to CO2 emissions, necessitating environmentally friendly alternatives. With its vast potential, seawater has garnered attention as a valuable resource for hydrogen production, especially in arid coastal regions with surplus renewable energy. Direct seawater electrolysis presents a viable option, although it faces challenges such as corrosion, competing reactions, and the presence of various impurities. To enhance the seawater electrolysis efficiency and overcome these challenges, researchers have turned to bipolar membranes (BPMs). These membranes create two distinct pH environments and selectively facilitate water dissociation by allowing the passage of protons and hydroxide ions, while acting as a barrier to cations and anions. Moreover, the presence of catalysts at the BPM junction or interface can further accelerate water dissociation. Alongside the thermodynamic potential, the efficiency of the system is significantly influenced by the water dissociation potential of BPMs. By exploiting these unique properties, BPMs offer a promising solution to improve the overall efficiency of seawater electrolysis processes. This paper reviews BPM electrolysis, including the water dissociation mechanism, recent advancements in BPM synthesis, and the challenges encountered in seawater electrolysis. Furthermore, it explores promising strategies to optimize the water dissociation reaction in BPMs, paving the way for sustainable hydrogen production from seawater.

Electron‐Donating Cu Atoms Induced High Proton Supply and Anti‐Poisoning Ruthenium Clusters for Superior Direct Seawater Hydrogen Production

AbstractDirect seawater hydrogen production via electrolysis would be a transformative technology for large‐scale pathways for future sustainable energy systems. However, prohibiting the formation of insoluble hydroxides and promoting proton supply at the electrode‐seawater interface are extremely desirable but remain challenging. Herein, inspired by the dual‐metal pair sites in natural enzyme, the de novo design of an efficient, robust, and precise electron‐donating Cu‐modulated ruthenium clusters on porous carbon matrix (Cu@Runc‐C) is reported as a high proton supply and anti‐poisoning cathode material for superior direct seawater hydrogen production. Benefitting from the unique Cu@Runc pair sites, the cathode exhibits particularly high hydrogen evolution activities with ultralow overpotentials to reach a high current density of 300 mA cm−2 in both alkaline (115 mV) and seawater (459 mV) electrolytes, and notably, the cathode can maintain superior long‐lasting stability in seawater electrolysis. The mechanism exploration demonstrates that the ruthenium cathode with Cu@Runc pair sites exhibits low oxophilic and fast proton‐transferring local reaction environments to prohibit the formation of insoluble precipitates and provide efficient proton supply within the electrode‐seawater interface. It is expected that the proposed bioinspired regulation strategy offers a new pathway for constructing efficient, robust, and selective cathode materials for scalable seawater hydrogen production.

A restricted dynamic surface self-reconstruction toward high-performance of direct seawater oxidation

The development of highly efficient electrocatalysts for direct seawater splitting with bifunctionality for inhibiting anodic oxidation reconstruction and selective oxygen evolution reactions is a major challenge. Herein, we report a direct seawater oxidation electrocatalyst that achieves long-term stability for more than 1000 h at 600 mA/cm2@η600 and high selectivity (Faraday efficiency of 100%). This catalyst revolves an amorphous molybdenum oxide layer constructed on the beaded-like cobalt oxide interface by atomic layer deposition technology. As demonstrated, a new restricted dynamic surface self-reconstruction mechanism is induced by the formation a stable reconstructed Co-Mo double hydroxide phase interface layer. The device assembled into a two-electrode flow cell for direct overall seawater electrolysis maintained at 1 A/cm2@1.93 V for 500 h with Faraday efficiency higher than 95%. Hydrogen generation rate reaches 419.4 mL/cm2/h, and the power consumption (4.62 KWh/m3 H2) is lower than that of pure water (5.0 KWh/m3 H2) at industrial current density.

Catalysts for Direct Seawater Electrolysis: Current Status and Future Prospectives

AbstractGlobal freshwater shortage is forcing researchers to focus on seawater electrolysis for large‐scale green hydrogen production. Seawater purification by reverse osmosis (RO) for use in conventional water electrolyzers (WEs) is another approach, however, that requires large capital investments. Alternatively, seawater can be used directly in a novel type of anion exchange membrane WE (AEMWE) which is currently under development. The AEMWEs have the advantage of using non‐precious catalysts and are less sensitive to the presence of impurities. Success in this early‐stage technology relies on the development of efficient and durable electrocatalysts. This paper provides a comprehensive review of the status and future trends for developing catalysts operating directly with seawater. Catalysts are ranked based on their activity and durability at high current densities of 500 mAcm−2 and 1000 mAcm−2. Notable anode catalysts, S−NiFe2O4, and NiFe LDH, exhibit reduced OER overpotentials of 287 mV and 296 mV at 1000 mAcm−2. Top‐performing cathode HER catalysts include HW−NiMoN‐2 h (132 mV) and Pt−Co−Mo (117 mV) at 1000 mAcm−2. Bifunctional catalysts, such as CoxPv@NC can operate below an overall voltage of 2 V at 1000 mAcm−2. This comparative analysis provides researchers and professionals with critical insights for advancing direct seawater electrolysis.

High-Entropy Carbonates (Ni-Mn-Co-Zn-Cr-Fe) as a Promising Electrocatalyst for Alkalized Seawater Oxidation

Direct seawater splitting has attracted considerable attention as an alternative to conventional alkaline water electrolysis because the former avoids the use of limited freshwater resources. However, several challenges must be overcome to realize direct seawater electrolysis. Most importantly, electrocatalysts for the anodic oxygen evolution reaction (OER) should exhibit high activity, stability, and selectivity in highly corrosive environments with abundant chloride ions. In this study, we developed high-entropy carbonate (HEC) as a promising electrocatalyst for seawater oxidation. In HECs, physicochemical interactions among different elements can effectively suppress the corrosion of OER active sites, while polyanionic CO32- can act as a corrosion-protective species by repelling negatively charged chloride ions during electrolysis. Consequently, HECs demonstrate outstanding catalytic activity, stability, and selectivity for seawater oxidation, surpassing those of ternary, quaternary, and quinary carbonates and even benchmark IrO2 catalysts.

Energy-Efficient Electrosynthesis of High Value-Added Active Chlorine Coupled with H2 Generation from Direct Seawater Electrolysis through Decoupling Electrolytes.

Direct saline (seawater) electrolysis is a well-recognized system to generate active chlorine species for the chloride-mediated electrosynthesis, environmental remediation and sterilization over the past few decades. However, the large energy consumption originated from the high cell voltage of traditional direct saline electrolysis system, greatly restricts its practical application. Here, we report an acid-saline hybrid electrolysis system for energy-saving co-electrosynthesis of active chlorine and H2. We demonstrate that this system just requires a low cell voltage of 1.59 V to attain 10 mA cm-2 with a large energy consumption decrease of 27.7 % compared to direct saline electrolysis system (2.20 V). We further demonstrate that such acid-saline hybrid electrolysis system could be extended to realize energy-saving and sustainable seawater electrolysis. The acidified seawater in this system can absolutely avoid the formation of Ca/Mg-based sediments that always form in the seawater electrolysis system. We also prove that this system in the half-flow mode can realize real-time preparation of active chlorine used for sterilization and pea sprout production.