Direct Seawater Research Articles

Phytic-acid-doped conductive hydrogels as alkaline seawater electrocatalysts with anomalous chloride promoted oxygen evolution reaction

The side reaction mainly caused by chloride ions in seawater is the key bottleneck restricting the development of efficient and stable oxygen evolution reaction (OER) electrocatalysts for direct seawater splitting. Recent researches on OER catalysts in seawater mostly concentrate on the repulsive force of Cl− to reduce its adverse impact. Here, we verified that Cl− doping into phytic acid based polypyrrole conductive hydrogel has no significant negative effect; On the contrary, it is beneficial to enhance its activity in seawater. A series of characterization techniques show that doping Cl in the polypyrrole conductive hydrogel can improve the conductivity and promote the electron transfer in the OER process. Therefore, we achieved direct alkaline seawater electrolysis using a non-metallic PA-PPy/CP anode in an alkaline electrolysis cell.

Ruthenium And Silver Synergetic Regulation NiFe LDH Boosting Long‐Duration Industrial Seawater Electrolysis

AbstractThe chloride ions in seawater result in corrosion, low catalytic efficiency, and poor stability of the electrocatalysts in direct seawater electrolysis, which limits the use of large‐scale seawater electrolysis technology. Herein, a corrosion‐resistant Ag/NiFeRu layered double hydroxide (LDH) electrocatalyst for seawater electrolysis at industrial current density, in which Ru and Ag species in the catalyst can have a corrosion‐resistance of chloride ions from the anode surface and enhance its robustness in seawater is designed. The catalyst requires the overpotentials of 256 and 287 mV to obtain a current density of 1 A cm−2 in 1 m KOH and 1 m KOH + seawater, respectively. More importantly, it works stably for over 1000 h at 1 A cm−2 in alkaline seawater. Further quasi‐industrial conditions measurement (6 m KOH + seawater, 60 °C) shows a markedly low overpotential of 174 mV at 1 A cm−2 on Ag/NiFeRu LDH, obtaining over 140 h under harsh industrial conditions. Theoretical calculations demonstrate that the Ru species can effectively regulate the local electronic structure of NiFe LDH, and enhance the intrinsic activity of NiFe LDH. The transformation of Ag2O from Ag during OER stabilizes the Fe site in NiFe LDH, which improves the overall stability of the electrocatalyst.

Stepwise strategies for overcoming limitations of membraneless electrolysis for direct seawater electrolysis

Direct seawater electrolysis (DSWE) has been investigated as a candidate solution for hydrogen (H2) production using abundant seawater without the water purification requirements of conventional electrolyzers. Costly perfluorinated membranes employed in contemporary water electrolyzers (PEMWE) fail in the presence of trace contaminants due to cation exchange for H+ and scaling resulting from Mg2+/Ca2+ hydroxide precipitation caused by local pH increases. Herein, we disclose a membraneless electrolyzer and explore how symmetric and asymmetric electrolyte recirculation schemes impact pH gradients and performance of the system using in-house developed near-neutral pH electrocatalysts. Under the asymmetric recycle scheme, unbuffered seawater feed can be used whereby pH differentials caused by electrolysis are re-balanced by recirculating the liquid anode and cathode effluent streams to the cathode and anode inlet ports, respectively. Cell voltages of 2.61 and 3.50 V were required to attain 100 mA cm−2 of current density under buffered (0.5 M phosphate buffer; pH 6.71) and unbuffered synthetic seawater operation, respectively, and 50 h of chronoamperometric stability at the same current density was achieved for the former. A mere 0.18 % of H2 crossover from the catholyte to the anolyte at 250 mA cm−2 of current density was recorded at prolonged operation.

Bifunctional Amorphous Transition-Metal Phospho-Boride Electrocatalysts for Selective Alkaline Seawater Splitting at a Current Density of 2Acm-2.

Hydrogen production by direct seawater electrolysis is an alternative technology to conventional freshwater electrolysis, mainly owing to the vast abundance of seawater reserves on earth. However, the lack of robust, active, and selective electrocatalysts that can withstand the harsh and corrosive saline conditions of seawater greatly hinders its industrial viability. Herein, a series of amorphous transition-metal phospho-borides, namely Co-P-B, Ni-P-B, and Fe-P-B are prepared by simple chemical reduction method and screened for overall alkaline seawater electrolysis. Co-P-B is found to be the best of the lot, requiring low overpotentials of ≈270mV for hydrogen evolution reaction (HER), ≈410mV for oxygen evolution reaction (OER), and an overall voltage of 2.50V to reach a current density of 2Acm-2 in highly alkaline natural seawater. Furthermore, the optimized electrocatalyst shows formidable stability after 10,000 cycles and 30h of chronoamperometric measurements in alkaline natural seawater without any chlorine evolution, even at higher current densities. A detailed understanding of not only HER and OER but also chlorine evolution reaction (ClER) on the Co-P-B surface is obtained by computational analysis, which also sheds light on the selectivity and stability of the catalyst at high current densities.

Technology mapping of direct seawater electrolysis through patent analysis

In recent years, climate change has become more intense for society, and to mitigate this scenario, renewable energy sources have increased their installed capacity. In this context, green hydrogen, which can be obtained through water electrolysis, is considered one of the main alternatives to enable the replacement of fossil energy sources, acting as an energy vector to balance supply and demand for renewable energy. This study aims to mapping trends in direct seawater electrolysis technology by analyzing patents retrieved from the Derwent Innovations Index database between 1963 and 2022. As a result, 138 patent documents were identified and the analysis revealed an increase in patenting between 2016 and 2021 leading by China, South Korea, Japan, the United States, and the United Kingdom. The analysis also showed a trend towards research and development for electrocatalysts for direct seawater electrolysis in alkaline media, using materials not belonging to the platinum group metals.

Polyvinylidene fluoride-based modified membranes for hydrogen generation by direct seawater electrolysis and proton exchange membrane fuel cells

Polyvinylidene fluoride-based modified membranes for hydrogen generation by direct seawater electrolysis and proton exchange membrane fuel cells

Challenges and progress in oxygen evolution reaction catalyst development for seawater electrolysis for hydrogen production.

Production of green hydrogen on a large scale can negatively impact freshwater resources. Therefore, using seawater as an electrolyte in electrolysis is a desirable alternative to reduce costs and freshwater reliance. However, there are limitations to this approach, primarily due to the catalyst involved in the oxygen evolution reaction (OER). In seawater, the OER features sluggish kinetics and complicated chemical reactions that compete. This review first introduces the benefits and challenges of direct seawater electrolysis and then summarises recent research into cost-effective and durable OER electrocatalysts. Different modification methods for nickel-based electrocatalysts are thoroughly reviewed, and promising electrocatalysts that the authors believe deserve further exploration have been highlighted.

Dynamic dual-atom synergistic catalysis boosted by liquid metal for direct seawater electroreduction

Dynamic Co, Pt dual-atom synergistic catalysis boosted by Ga-based liquid metal for direct seawater electroreduction.

Heterostructured NiTe/Ni2P nanoarrays as high-activity electrocatalysts for the oxygen evolution reaction in seawater splitting

Scale-up hydrogen production from natural seawater presents a promising avenue to address the escalating depletion of fossil fuel resources. However, direct seawater splitting (DSS) remains a formidable challenge, primarily due to the deficiency of efficient, stable, and cost-effective catalysts for the oxygen evolution reaction (OER). In this paper, we demonstrate the fabrication of a self-supported heterostructured nanoarray electrocatalyst, namely, NiTe/Ni2P, which exhibits exceptional performance and durability in the OER in alkaline seawater conditions. Remarkably, this innovative catalyst displays an overpotential of merely 312 mV to achieve a current density of 100 mA cm−2. Moreover, the overall seawater splitting (OSS) process can be achieved at a cell voltage of 1.68 V while maintaining a high faradic efficiency (FE) of nearly 100 % for the OER, alongside exceptional stability exceeding 100 h of continuous testing. We have validated the presence of heterostructures and strong interactions between NiTe and Ni2P, as well as the Cl- repelling capability resulting from the incorporation of P, which induces a more negatively charged surface. These aforementioned factors are posited as the fundamental drivers behind the catalyst's extraordinary performance and steadfastness in the OER during DSS. Moreover, this strategic approach harbors tremendous potential for the systematic development of catalysts exhibiting exceptional OER performance within the realm of DSS.

Alkaline-earth-metal regulated metal carbides with bioinspired gradient OH spillover for efficient and long-lasting direct seawater electrolysis

Alkaline-earth-metal and Ru atom co-engineered catalysts with a gradient OH spillover pathway on metal carbide have been realized with retard formation of precipitates and efficient proton supply for efficient and long-lasting seawater electrolysis.

Innovations in electrocatalysts, hybrid anodic oxidation, and electrolyzers for enhanced direct seawater electrolysis

This review focuses on the latest developments in direct seawater electrolysis, specifically in electrocatalysts, hybrid anodic oxidation, and electrolyzers, providing a glimpse into the future of environmentally friendly hydrogen generation.

Electrochemical reconstruction of non-noble metal-based heterostructure nanorod arrays electrodes for highly stable anion exchange membrane seawater electrolysis

Direct seawater electrolysis for hydrogen production has been regarded as a viable route to utilize surplus renewable energy and address the climate crisis. However, the harsh electrochemical environment of seawater, particularly the presence of aggressive Cl−, has been proven to be prone to parasitic chloride ion oxidation and corrosion reactions, thus restricting seawater electrolyzer lifetime. Herein, hierarchical structure (Ni,Fe)O(OH)@NiCoS nanorod arrays (NAs) catalysts with heterointerfaces and localized oxygen vacancies were synthesized at nickel foam substrates via the combination of hydrothermal and annealing methods to boost seawater dissociation. The hierarchical nanostructure of NiCoS NAs enhanced electrode charge transfer rate and active surface area to accelerate oxygen evolution reaction (OER) and generated sulfate gradient layers to repulsive aggressive Cl−. The fabricated heterostructure and vacancies of (Ni,Fe)O(OH) tuned catalyst electronic structure into an electrophilic state to enhance the binding affinity of hydroxyl intermediates and facilitate the structural transformation into amorphous γ-NiFeOOH for promoting OER. Furthermore, through operando electrochemistry techniques, we found that the γ-NiFeOOH possessing an unsaturated coordination environment and lattice-oxygen-participated OER mechanism can minimize electrode Cl− corrosion enabled by stabilizing the adsorption of OH* intermediates, making it one of the best OER catalysts in the seawater medium reported to date. Consequently, these catalysts can deliver current densities of 100 and 500 mA cm−2 for boosting OER at minimal overpotentials of 245 and 316 mV, respectively, and thus prevent chloride ion oxidation simultaneously. Impressively, a highly stable anion exchange membrane (AEM) seawater electrolyzer based on the non-noble metal heterostructure electrodes reached a record low degradation rate under 100 μV h−1 at constant industrial current densities of 400 and 600 mA cm−2 over 300 h, which exhibits a promising future for the non-precious and stable AEMWE in the direct seawater electrolysis industry.

Hydrogen Production with Seawater-Resilient Bipolar-Membrane Electrolyzers

Commercial proton exchange membrane water electrolyzers (PEMWEs) are highly efficient when operating in ultra-pure de-ionized water. However, introduction of additional ions leads to a reduction in device durability and efficiency. Chloride (Cl-) ions, typically found in high concentrations in seawater, lead to device performance issues driven in part by the chlorine evolution reaction at the anode. At the acidic anode-cation exchange layer interface, corrosive chlorine species (OCl-, HOCl, Cl-) are readily generated due to the facile kinetics of the 2-electron oxidation reaction relative to the desired 4-electron water oxidation reaction. Bipolar membrane water electrolyzers (BPMWEs), however, contain a locally basic anode-anion exchange layer interface, leading to improved thermodynamic favorability for O2 production rather than corrosive chlorine species production. Furthermore, the bipolar membrane can readily block anions and cations from accessing the desired reaction spaces. In this work, we evaluated ion transport, chloride oxidation, and durability of BPMWEs and PEMWEs operating in salt water. BPMWEs exhibit a low Faradaic efficiency of 0.005% for the oxidation of Cl− to corrosive chlorine species at the anode, compared to PEMWEs that can reach a Faradaic efficiency of up to 10% under similar conditions. In addition, BPMWEs demonstrate a device lifetime that is 140 times longer than that of PEMWEs operating in direct seawater electrolysis conditions. Failure modes for each membrane type have been investigated under both ultra-pure and impure water electrolysis conditions and are discussed in this work.

Direct Seawater Electrolysis: From Catalyst Design to Device Applications.

Direct seawater electrolysis (DSE) for hydrogen production, using earth-abundant seawater as the feedstock and renewable electricity as the driving source, paves a new opportunity for flexible energy conversion/storage and smooths the volatility of renewable energy. Unfortunately, the complex environments of seawater impose significant challenges on the design of DSE catalysts, and the practical performance of many current DSE catalysts remains unsatisfactory on the device level. However, many studies predominantly concentrate on the development of electrocatalysts for DSE without giving due consideration to the specific devices. To mitigate this gap, the most recent progress (mainly published within the year 2020-2023) of DSE electrocatalysts and devices are systematically evaluated. By discussing key bottlenecks, corresponding mitigation strategies, and various device designs and applications, the tremendous challenges in addressing the trade-off among activity, stability, and selectivity for DSE electrocatalysts by a single shot are emphasized. In addition, the rational design of the DSE electrocatalysts needs to align with the specific device configuration, which is more effective than attempting to comprehensively enhance all catalytic parameters. This work, featuring the first review of this kind to consider rational catalyst design in the framework of DSE devices, will facilitate practical DSE development.

Transition metal sulfide and nickel-iron layered double hydroxide nanohybrids for promising alkaline seawater oxidations

Direct seawater electrolysis is of great significance to produce green hydrogen using sustainable resources which can be applicable for water-scarce regions. Herein, a nanohybrid consisted of transition metal sulfide and layered double hydroxide is designed with aims to modify unfavorable surface electronic state of nickel–iron LDH (NF-LDH) for seawater oxidation. Specifically, Mo-doped NiS2 is deposited onto the self-standing two dimentional NF-LDH nanosheets, (Ni,Mo)S2//NF-LDH 300, using an e-beam evaporator. Physical deposition technique. The designed (Ni, Mo)S2//NF-LDH 300 catalyst proves a superior catalytic activity and stability for seawater oxidation under alkaline electrolyte. The deposited transition sulfide layer induces an improved charge transfer as well as reaction kinetics for the (Ni, Mo)S2//NF-LDH 300. Further, adsorptions of chloride anions at the surface is substantially suppressed due to the deposited transition metal sulfide effectively preventing chloride corrosions. The (Ni, Mo)S2//NF-LDH 300 demonstrates practical level of performance for alkaline seawater oxidation, shedding lights on our catalyst design strategy for direct seawater electrolysis.

Direct seawater splitting by photo-piezoelectric coupling based on surface protonated perovskite

Photocatalytic water splitting for hydrogen evolution has become one of the most important and effective ways to produce green and renewable hydrogen energy, the centre of which is the efficient, stable and inexpensive photocatalyst. The part of perovskite oxides have a wide range of properties such as ferroelectricity, piezoelectricity and pyroelectricity, as well as good photoresponsivity and chemical stability, which are promising for catalytic conversion applications. In this study, the Ruddlesden-Popper (RP) phase perovskite La2NiO4 is investigated from enhanced charge separation as well as accelerated surface redox reaction rates. In the case of the existence of piezoelectric response of La2NiO4, the photo-piezoelectric coupling strategy not only realize the catalytic pure water splitting, but also greatly improve the efficiency. The lattice structure is twisted when the catalyst is subjected to external stress and the electric dipole moment is no longer zero. The resulting piezoelectric potential not only enables the free charge in the bulk phase to migrate directionally, but also inhibits the recombination of photogenerated carriers, which ultimately achieves highly efficient photo-piezoelectric coupling for water splitting for hydrogen production. In addition, the protonation of the catalyst surface is used to further enhance the interfacial reaction of the catalysts, which improves the solution-catalysts contact efficiency and generates vacancy defects to strengthen the spontaneous polarization of the lattices, contributing to the enhancement of the redox reaction rate. This optimization strategy of surface protonation treatment combined with photo-piezoelectric coupling is not only applicable to nanocatalyst powders but also has a significant enhancement effect in perovskite ceramic membranes. When La2NiO4 powders are sintered into the porous ceramic membrane and the surface is protonated with 0.006 mol L−1 hydrochloric acid, the hydrogen production rate of seawater splitting under the photo-piezoelectric coupling condition can reach 7750.41 μmol m−2 h−1. This study contributes to further understanding of photo-piezoelectric coupling catalysis, leading to a new solutions for expanding the application of coupled multifield water splitting for hydrogen evolution.

Seawater to Green Hydrogen: Future of Green Energy

AbstractWater electrolysis to produce hydrogen has been viewed as the future of green energy. The reliance of current electrolyzer technologies on ultrapure fresh water is not feasible to meet increasing hydrogen demands. The abundant seawater emerged as the potential feedstock for water electrolysis, but its complex composition and chlorine chemistry make the process complicated. Recently designed effective catalysts have given hope for direct seawater splitting but need to be optimized for commercial use. Moreover, the inability of current electrolyzer technologies with seawater requires efforts to establish this technology. In short, freshwater as feed for water electrolysis is not sustainable; the focus must be on seawater. While desalination seems to be a viable option, the economics of scale of the plant is critical in assessing its viability. Although the complex composition of seawater makes direct seawater splitting challenging, designing effective catalysts and durable electrolyzers can make it possible for a truly sustainable hydrogen industry.

Boosting Direct Seawater Electrolysis through Intercalation Engineering of Layered Double Hydroxides

Boosting Direct Seawater Electrolysis through Intercalation Engineering of Layered Double Hydroxides

Engineering dual MoC–Mo2C heterostructure–knotted CNTs for efficient direct seawater electrolysis

Considering the abundant reserves of seawater and limited resources of freshwater, seawater electrolysis is a more economically competitive technology for producing high-purity hydrogen, but remains a challenging approach. Herein, we report an innovative strategy for constructing dual MoC–Mo2C heterostructure–knotted CNTs nanorods (MoC–Mo2C/CNTs) to improve the electrocatalytic performance and durability in alkaline seawater, in which the hybrid electrode achieves 10 mA cm−2 at low overpotentials of 95 and 279 mV for HER and OER, respectively. For overall simulated and natural seawater splittings, a low cell voltage of 1.57 and 1.61 V, respectively, is necessary to drive 10 mA cm−2 and outstanding durability over 50 h at a high current density of 50 mA cm−2. The experimental results indicate that the unique boundary interface of MoC–Mo2C/CNTs could result in rich exposed active sites, corrosion resistance layer, and electronic redistribution, thus leading to high-performance HER and OER activities. This work provides an ultimate approach to the rational design of multi-component transition metal carbide-based heterogeneous electrocatalysts for seawater electrolysis.

Development of Janus membranes with asymmetric wettability for desalination of impaired seawater by direct contact membrane distillation

Membrane distillation (MD) is an emerging technology for direct seawater desalination. The widely employed hydrophobic membranes are susceptible to pore wetting/ fouling in the presence of organic contaminants in seawater. Here, we demonstrate a facile method of preparing Janus membranes with hydrophilic/hydrophobic faces having excellent anti-fouling and anti-wetting properties. The hydrophobic substrate is a PVDF-co-HFP membrane incorporating fluoroalkylsilane (FAS) grafted hydrophobic MIL-53(Al)- a form of metal organic framework (h-MIL-53(Al)), and the hydrophilic coating is prepared by the direct deposition of polydopamine (PDA) (top layer). The optimum membrane exhibited a stable flux of 11 L/m2h and permeate conductivity ∼10 µS/cm for up to 60 h of seawater desalination. The anti-wetting property of the Janus membrane was demonstrated from the stable performance when challenging the membrane with impaired seawater containing low surface tension compounds such as sodium dodecyl sulphate (SDS) and propylene glycol (PG), and oil (hexadecane). The prepared membrane exhibited wetting resistance of 45 h and 18 h when feed was seawater containing 0.3 mM SDS and 3 wt% PG, respectively. The membrane displayed excellent resistance to fouling for desalination from SDS-stabilized hexadecane (500 ppm)/seawater feeds for up to 50 h (5 cycles). The membrane fabricated in this study holds the potential for seawater desalination.