Seawater Electrolyte Research Articles

Oxophilic vanadium and deprotonated ruthenium atoms on tungsten carbide with accelerated intermediate migration for high-performance seawater hydrogen evolution

Compared with traditional freshwater electrolysis, the seawater electrolysis process is confronted with low activity and poor stability problems due to the deposition of insoluble hydroxides and corrosion of chloride species; thus, engineering efficient catalysts for seawater electrolysis are extremely desirable but remain challenging. Herein, we have developed an efficient and robust electrocatalyst by engineering oxophilic vanadium and deprotonated ruthenium atoms on tungsten carbide (WC-RuV) as a highly active and anti-poisoning cathode material for superior seawater electrolysis. Benefiting from the high oxophilicity and electron transfer ability of V, the interaction between the OH* generated via water dissociation and Ru sites is weakened, which facilitates the OH* transfer process and consequently attenuates the formation of insoluble hydroxides. Notably, when working in simulated seawater electrolytes, the WC-RuV requires an ultralow overpotential, and the WC-RuV@carbon cloth can maintain high activity and stability even at 200 mA cm−2. The assembled WC-RuV||RuO2 anion exchange membrane (AEM) electrolyzer realizes long-term stability at the current of 100 mA cm−2 and achieves continuous operation powered by commercially available solar panels. This work provides an efficient strategy for modulating the water dissociation process and offers a new perspective for designing high-performance catalysts for the forthcoming application of seawater electrolysis.

Nickel-Cobalt Bimetal Hierarchical Hollow Nanosheets for Efficient Oxygen Evolution in Seawater.

The electrochemical splitting of seawater is promising but also challenging for sustainable hydrogen gas production. Herein, ZIF-67 nanosheets are grown on nickel foam and then etched by Ni2+ in situ to obtain a hierarchical hollow nanosheets structure, which demonstrates outstanding OER performance in alkaline seawater (355 mV at 100 mA cm-2). Diven by a silicon solar panel, an overall electrolysis energy efficiency of 62% is achieved at a high current of 100 mA cm-2 in seawater electrolytes. This work provides a new design route for improving the catalytic activity of metal organic framework materials.

Different M-doped Ni3S2/FeS (M=Co, Cr, Cu, Zn) hybrid nanosheet arrays for overall urea splitting and seawater oxidation reaction

Hydrogen production by electrolysis of water is gradually becoming the main way to obtain green energy, but due to the scarcity of fresh water resources in the world, so the study of urea and seawater electrolysis has become an important work. In this experiment, different metal ions M (M=Co, Cr, Cu, Zn) doped Ni3S2/FeS were investigated as catalysts with good catalytic activity in hydrogen evolution reaction (HER) as well as in urea oxidation reaction (UOR) in urea electrolyte, and Co-Ni3S2/FeS and Cr-Ni3S2/FeS, which performed well in HER and UOR, were assembled into an electrolytic cell for the overall urea decomposition (1.50 V @ 10 mA cm−2). Density Functional Theory (DFT) calculations demonstrated that Co-Ni3S2 possesses a lower free energy for H, while FeS possesses a higher density of states (DOS) near the Fermi energy level, and such a composite structure promotes significantly the catalytic activity of HER. The catalytic effect of oxygen evolution reaction (OER) was further investigated in the seawater electrolyte, and the results showed that the performance of Co-Ni3S2/FeS catalyst was better, and certain ions in seawater affected durability of the catalyst. The electronic structure of the catalyst was investigated through the characterization of the catalyst and combined with the special morphology jointly promote the catalytic reaction in electrolysis experiments, which provides a candidate catalyst for electrolysis of urea and seawater oxidation reaction.

Boron modification promoting electrochemical surface reconstruction of NiFe-LDH for efficient and stable freshwater/seawater oxidation catalysis

Transition metal-based electrocatalysts generally take place surface reconstruction in alkaline conditions, but little is known about how to improve the reconstruction to a highly active oxyhydroxide surface for an efficient and stable oxygen evolution reaction (OER). Herein, we develop a strategy to accelerate surface reconstruction by combining boron modification and cyclic voltammetry (CV) activation. Density functional theory calculations and in-situ/ex-situ characterizations indicate that both B-doping and electrochemical activation can reduce the energy barrier and contribute to the surface evolution into highly active oxyhydroxides. The formed oxyhydroxide active phase can tune the electronic configuration and boost the OER process. The reconstructed catalyst of CV-B-NiFe-LDH displays excellent alkaline OER performance in freshwater, simulated seawater, and natural seawater with low overpotentials at 100 mA cm−2 (η100: 219, 236, and 255 mV, respectively) and good durability. This catalyst also presents outstanding Cl− corrosion resistance in alkalized seawater electrolytes. The CV-B-NiFe-LDH||Pt/C electrolyzer reveals prominent performance for alkalized freshwater/seawater splitting. This study provides a guideline for developing advanced OER electrocatalysts by promoting surface reconstruction.

Efficient optimization of electron transfer pathway by constructing phosphide/ceria interface boosts seawater hydrogen production

Developing efficient and durable hydrogen evolution reaction (HER) electrocatalysts is one of the most important issues for the commercialization of seawater electrolysis, but it remains challenging. Here, we report a CeO2-CoP nanoneedle array catalyst loaded on Ti mesh (CeO2-CoP/TM) with work-function-induced directional charge transport properties. The CeO2-CoP/TM catalyst showed superior HER catalytic activity and stability, with overpotentials of 41 and 60 mV to attain 10 mA cm−2, in 1 M KOH and 1 M KOH + seawater electrolyte, respectively. Experimental results and theoretical calculations reveal that the work function drives the charge transfer from CeO2 to CoP, which effectively balances the electronic density of CoP and CeO2, optimizes the d-band center, and accelerates the water activation kinetics, thus enhancing the HER activity. The solar-driven water electrolysis device displays a high and stable solar-to-hydrogen conversion efficiency of 19.6%. This study offers a work function-induced directional charge transport strategy to design efficient and durable catalysts for hydrogen production.

Coupled amorphous NiFeP/cystalline Ni3S2 nanosheets enables accelerated reaction kinetics for high current density seawater electrolysis

Rational designing efficient, low-cost and corrosion resistant electrocatalysts is a crucial priority for seawater electrolysis to give impetus to the development of hydrogen energy and carbon neutrality. Herein, an amorphous NiFeP/crystalline Ni3S2 (NiFeP/Ni3S2) heterojunction catalyst is legitimately constructed for seawater electrolysis. Such structure improves the conductivity of amorphous NiFeP and optimizes the electronic structure by keeping the metal active sites in a relatively high valence state. In situ/ex situ experimental and theoretical calculation results reveal that the amorphous/crystal heterostructure accelerates the reconstruction and reaction kinetics of catalysts, reducing the energy barrier for potential-determining step and leading to improved intrinsic activity. The constructed NiFeP/Ni3S2 shows the overpotential of 354 mV to drive current density of 800 mA cm−2 in the alkaline medium. Besides, under 100 mA cm−2, NiFeP/Ni3S2 can run stably for 600 hours in seawater electrolyte without any hypochlorite production, demonstrating its excellent chemical stability and corrosion resistance.

Polyoxometalate-derived bi-functional crystalline/amorphous interfaces with optimized d-electron configuration for efficient self-powered hydrazine-seawater splitting

Hydrazine-assisted water electrolysis is a promising energy-efficient strategy for hydrogen production. Nonetheless, developing high-performance bi-functional electrocatalysts towards both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) remains great challenges, especially for hydrazine-seawater splitting. Herein, we report a polyoxometalate-assisted in-situ synthesis protocol for constructing bi-functional crystalline/amorphous Pt/MoO3-x interfaces toward both efficient HER and HzOR. The polyoxometalate-derived crystalline/amorphous Pt/MoO3-x interfaces deliver working potentials of only –23 and −41 mV at 10 mA cm−2 for HER and HzOR in seawater electrolyte, respectively. Meanwhile, ultrahigh mass activities of 38.39 AmgPt-1 for HER at −100 mV potential and 23.84 AmgPt-1 for HzOR at 50 mV potential are also achieved, over 30.2 and 52.9 times higher than those of commercial Pt/C. As bi-functional electrocatalysts for overall hydrazine-seawater splitting, the electrolyzer requires a cell voltage of only 55/238 mV at 10/100 mA cm−2, 1.584/1.543 V lower than that of the seawater splitting system. Moreover, a proof-of-concept self-powered hydrazine-seawater electrolysis system driven by direct hydrazine fuel cell is further demonstrated, which achieves a hydrogen production rate of 0.29 mL cm−2min−1. DFT calculations verify that, the crystalline/amorphous interfaces endow Pt/MoO3-x an optimized d-electron configuration with favorable H* adsorption and promoted dehydrogenation kinetics of *N2H4 to *N2H3 in the potential-determining step. This work provides a novel strategy and inspiration toward the design of efficient bi-functional electrocatalysts for hydrazine-assisted 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.

Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42− anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl− on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42− distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42− even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42−. Density functional theory calculations also reveal that the adsorption of CrO42− can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

In situ generation of oxyanions-decorated cobalt(nickel) oxyhydroxide catalyst with high corrosion resistance for stable and efficient seawater oxidation

The development of efficient and robust anode materials for stable alkaline seawater electrolysis is severely limited by chlorine evolution reaction and chloride corrosion. Here, the sulfur-doped cobalt-nickel bimetallic phosphides (CoNiPS) are specifically designed as a pre-catalyst for navigating a surface reconstruction to fabricate the anions (PO43− and SO42−)-decorated Co(Ni)OOH catalyst (R-CoNiPS) with exceptional durability and high activity for stable alkaline seawater oxidation (ASO). Various experiment techniques together with theoretical simulations both demonstrate that the in situ-generated PO43− and SO42− anions on catalyst surface can improve the oxygen evolution reaction (OER) activity, regulating and stabilizing the catalytic active species Co(Ni)OOH, as well as make a critical role in inhibiting the adsorption of chloride ions and extending the service life of electrode. Therefore, this R-CoNiPS electrode exhibits superb OER activity toward ASO and stands out among the non-precious ASO electrocatalysts reported recently, requiring low overpotentials of 420 and 440 mV to attain large current densities of 500 and 1000 mA cm−2 in an alkaline natural seawater electrolyte, respectively. Particularly, the catalyst displays a negligible chloride corrosion at room temperature during ASO operation (>200 h) at 500 mA cm−2. This work opens up a new viewpoint for designing high-activity and durable electrocatalysts for seawater electrolysis.

Unravelling the deposition of Zn and Sn as corrosion inhibitor on aluminum (Al) surface for Al-air battery application with sodium chloride electrolytes

Recently, Aluminum (Al) has been extensively developed as an anode material for Al-air batteries. High corrosion rate and slow kinetic reactions of Al in anode application drive the recent research to coat with other more noble metals. Therefore, the primary objective of this work is identifying the effect of zinc (Zn) and tin (Sn) coating on high purity Al surface for electrochemical properties improvement. The employed method of metal oxide coating was electrodeposition process. The structural and morphological of electrodeposition was investigated by scanning electron microscopy (SEM). The surface of Zn-Al was finer than Sn–Al. Additionally, the observed cracks on the surface were analyzed and interpreted as indicative of mixed metal oxide (MMO) coating behavior. In electrochemical performance, the Zn–Al half-cell exhibits a consistent open circuit potential value of −0.94 V. This value is the most stable compared with other variables. Remarkably, the discharge time that represents full-cell of Zn–Al and N-doped carbon-based cathode performance was about 14 h, which is nearly fourteen orders compared with Al variables that can only sustain in an hour. The electrodeposition also contributes to enhancing the specific capacity from 40.763 m Ah g−1 to become 324.627 mAh g−1. In line with other measurements, the corrosion rate with linear polarization measurement placed Zn–Al with the smallest corrosion rate, that is 3.71 × 10-5 mm/year. All the electrochemical measurements used 3.5 % NaCl as the model of seawater electrolytes. This finding could be a reliable option of aluminum air battery development on larger scale in the future.

Unique CoP Microflower Decorated with Phosphorous‐Enriched PtP2 onto Nickel Foam with Interfacial Electronic Interactions to Boost Alkaline Water‐Splitting

AbstractThe development of stable and efficient electrocatalysts for overall freshwater/seawater water‐splitting has received significant attention. In this study, the fabrication and electrocatalytic properties of phosphorus‐enriched PtP2 dispersed on CoP (PtP2/CoP) for HER and OER in both alkaline fresh/seawater media are described. Physical characterization and density functional theory calculations reveal that strong electronic interfacial interactions between PtP2 and CoP optimized the reaction kinetics by regulating the adsorption/desorption of intermediates and the cleavage of reactants. Additionally, operando electrochemical impedance spectroscopy reveals that PtP2/CoP significantly decreased phase angle with increasing applied potential compared with CoP, demonstrating that the construction of heterostructure provides a faster charge transfer on the surface and in the inner layer. Notably, the catalyst only requires overpotentials of 101 and 298 mV to achieve a benchmark of 100 mA cm−2 in alkaline freshwater for HER and OER. Moreover, the prepared catalyst featured overpotentials of 108 and 330 mV in an alkaline seawater electrolyte. Furthermore, a stable and high‐efficiency water electrolysis operation can be achieved using PtP2/CoP as both the anode and cathode (1.63 V@100 mA cm−2) coupled with satisfactory durability. This finding provides a deeper comprehension of the interaction of Pt‐less compounds and matrix in electrocatalysis for bifunctional electrocatalysts.

High-entropy spinel (FeCoNiMnAl)3O4 with three-dimensional microflower structure for stable seawater oxidation

In this study, high-entropy spinel (FeCoNiMnAl)3O4 catalyst with a three-dimensional(3D) layered microflower structure assembled by nanosheets grown on Ni foam (NF) is synthesized for stable seawater oxidation. Density functional theory (DFT) calculations indicate that it has a strong charge transfer capability, thereby reducing the energy barrier and boosting the reaction. As a result, a low oxygen evolution reaction (OER) overpotential of 274 mV@50 mA cm−2 is achieved with a small Tafel slope of 47.79 mV dec−1 in 1 M KOH solution. Notably, DFT calculations further verify that it shows stronger adsorption of OH than Cl. As expected, the required overpotentials are still as low as 284 and 295 mV@50 mA cm−2 in alkaline simulated seawater and natural seawater electrolytes. Also, it exhibits excellent stability and corrosion resistance, maintaining stable OER activity over 50 h at 500 mA cm−2 in alkaline natural seawater, which has the potential to realize industrial electrochemical seawater splitting.

Identifying the two-electron oxygen reduction mechanism on BC3 site in Cl−-containing electrolytes

The electrochemical synthesis of H2O2 has great potential for applications in the treatment of environmental pollution and energy, but the toxic effect of Cl− on the active sites of catalysts has severely limited the application of this technology in these fields. Developing efficient non-metal-doped catalysts represents an effective strategy to address this issue. Although B-doped carbon materials have demonstrated excellent ORR activity, the understanding of the ORR mechanism on B surface sites remains highly controversial, particularly in seawater electrolytes. The influence of Cl− adsorption behavior on the catalytic reaction center mechanism is still unknown. In this paper, catalysts containing the BC3 structure were successfully prepared with an H2O2 yield of 3.55 mol/ (gcat h) in simulated seawater. The DFT results demonstrated that BC3 functions as a 2e− ORR active site, and the presence of Cl− does not poison it. Instead, it promotes the hydrogenation process of *OOH on its surface, further enhancing its ORR performance. The results provide clarity on how the Cl− of the catalytic environment affects the ORR performance and pathway selectivity of non-metallic B-sites. Additionally, the results offer valuable insights for designing electrocatalysts in complex environments.

Self-supported FeCoNiCuP high-entropy alloy nanosheet arrays for efficient glycerol oxidation and hydrogen evolution in seawater electrolytes

Self-supported FeCoNiCuP high entropy alloy nanosheet arrays electrocatalyst was developed for highly efficient glycerol oxidation to formate and hydrogen evolution in seawater electrolytes.

Electrolyte-assisted polarization leading to enhanced charge separation and solar-to-hydrogen conversion efficiency of seawater splitting

Photocatalytic splitting of seawater for hydrogen evolution has attracted a great deal of attention in recent years. However, the poor energy conversion efficiency and stability of photocatalysts in a salty environment have greatly hindered further applications of this technology. Moreover, the effects of electrolytes in seawater remain controversial. Here we present electrolyte-assisted charge polarization over an N-doped TiO2 photocatalyst, which demonstrates the stoichiometric evolution of H2 and O2 from the thermo-assisted photocatalytic splitting of seawater. Our extensive characterizations and computational studies show that ionic species in seawater can selectively adsorb on photo-polarized facets of the opposite charge, which can prolong the charge-carrier lifetime by a factor of five, leading to an overall energy conversion efficiency of 15.9 ± 0.4% at 270 °C. Using a light-concentrated furnace, a steady hydrogen evolution rate of 40 mmol g−1 h−1 is demonstrated, which is of the same order of magnitude as laboratory-scale electrolysers.

Architecting a 1T-phase material with metal NPs enriching HER kinetics in alkaline and seawater electrolytes

In this study, we performed experiments to determine the necessity and importance of the 1T phase TMD performance in alkaline (1 M KOH) and seawater HER.

Iron-impregnated cellulosic carbon as an effective electrocatalyst for seawater oxidation.

The quest for cost effective but active electrocatalysts for water oxidation is at the forefront of research towards hydrogen economy. In this regard, bamboo as biomass derived N-doped cellulosic carbon has shown potential electrocatalytic performance towards water oxidation. The impregnation of optimum metallic Fe boosts the performance further, achieving an overpotential value of 238 mV at a benchmark current density of 10 mA cm-2. Owing to its promising OER performances in alkaline freshwater, the electrocatalyst was further explored in alkaline saline water and alkaline real seawater, exhibiting overpotentials of 272 mV and 280 mV, respectively, to reach 10 mA cm-2 current density. Most importantly, the protective graphitic multilayer surrounding the metallic Fe allowed the electrocatalyst to demonstrate excellent durability over 30 h even at a high current density in alkaline real seawater electrolyte.

Reconstruction Co-O-Mo in amorphous-crystalline MoOx/Co(OH)2 interface for industry-level active and stable electrocatalytic seawater hydrogen evolution

The activity of molybdenum (Mo)-based catalysts is significantly limited by the dissolution of Mo under alkaline conditions. Herein, using the dissolution of Mo in electrolysis, we firstly developed a feasible method to prepare an amorphous-crystalline MoOx/Co(OH)2 interfacial electrocatalysts with high activity and corrosion resistance on nickel foam (MoOx/Co(OH)2/NF). Notably, the dissolution of Mo accelerated the self-reconstruction process to favorably generate highly active and stable Co-O-Mo6+ species. Among them, high-valence Mo6+ in Co-O-Mo species can accumulate a large number of electrons at the O sites, thus optimizing p-band center of O sites and enhance the hydrogen adsorption ability (ΔGH* = 0.05 eV). Meanwhile, in-situ formed MoO42- and Co(OH)2 in MoOx/Co(OH)2/NF could inhibit the damage of metals ions and Cl- to O active species, and thereby enhancing its stability in electrocatalytic seawater splitting. As expected, the catalyst displayed a superior activity with ultralow overpotentials (HER: 215 mV @ 1000 mA·cm −2) and high stability for 1000 h at 500 mA·cm−2 in alkaline seawater electrolytes. In all, this study can provide a new route to prepare highly-active and corrosion-resistant electrocatalysts via self-reconstruction, and further the development of industrial hydrogen production.

Interface engineering of heterogeneous NiMn layered double hydroxide/vertically aligned NiCo2S4 nanosheet as highly efficient hybrid electrocatalyst for overall seawater splitting

We report the fabrication of a heterogeneous catalyst through vertically aligned NiCo2S4/Ni3S2 nanosheet with encapsulation of ultrathin NiMn layered double hydroxide over self-standing nickel foam (NM/NCS/NS/NF) via two-step hydrothermal processes. Benefiting from more adequate catalytic active centres and copious interfacial charge transfer channels, NM/NCS/NS/NF electrode demonstrates superior bifunctional activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes under alkaline fresh/simulated seawater electrolyte conditions. As a result, NM/NCS/NS/NF electrode requires the smallest overpotentials of 282 & 312 mV (OER) and 171 & 204 mV (HER) to attain current densities of 30 & 50 mA cm−2 respectively under alkaline simulated seawater electrolyte conditions. Besides, the presence of amorphous NiMn LDH layers over crystalline NiCo2S4/Ni3S2 catalyst stimulates surface adsorption of oxygen intermediate species, water dissociate ability on catalytic active centres, and mass transport with electron transfer at the interface. Further, the two-electrode configuration assisted electrolyser system delivers an efficient overall water splitting activity with minimum cell voltages of 1.54 V (in 1 M KOH) and 1.56 V (in 1 M KOH+0.5 M NaCl) at a current density of 10 mA cm−2. Besides, a fabricated electrolyser cell provides a more sustained water electrolysis process and robust durability for 20 h which displays NM/NCS/NS/NF electrode is a vibrant and potential candidate for realistic seawater electrolysis. Therefore, our proposed heterogeneous electrocatalyst could open up a new platform for developing efficient large-scale efficient seawater electrolysis.