Alkaline Seawater Research Articles

Layered Double Hydroxides with Carbonate Intercalation as Ultra‐Stable Anodes for Seawater Splitting at Ampere‐Level Current Density

AbstractOwing to the presence of a substantial concentration of chlorine in seawater, the anode still faces severe chlorine corrosion, especially the water splitting operated at high current densities. Herein, the cost‐effective and scalable NiFe layered double hydroxides with carbonate intercalation (named as NiFe LDH_CO32−) are synthesized utilizing the etching‐hydrolysis and ion exchange strategies under ambient conditions. Experimental findings demonstrate that NiFe LDH_CO32− shows excellent stability at 500 and 1000 mA cm−2 for 1000 h under alkaline simulated seawater. Additionally, a two‐electrode system offers great stability at current densities ranging from 100 to 1000 mA cm−2 over a duration of 400 h in alkaline seawater. This remarkably catalytic stability can be ascribed to the etching‐hydrolysis and carbonate intercalation strategies. The etching‐hydrolysis strategy leads to an integrated electrode for the catalyst‐carrier, enhancing the adhesion between them, and retarding hence the divorce of catalysts from the carrier. Theoretical calculations suggest that the carbonate intercalation weakens the adsorbability of chlorine on catalysts and hinders the coupling of metal atoms with chlorine, thereby impeding the anode corrosion caused by chlorine and improving catalytic stability. More importantly, this strategy has been extended to the preparation of other layered double hydroxides with carbonate intercalation.

Multicomponent nickel-molybdenum-tungsten-based nanorods for stable and efficient alkaline seawater splitting

The electrolysis of seawater for hydrogen production holds promise as a sustainable technology for energy generation. Developing water-splitting catalysts with low overpotential and stable operation in seawater is essential. In this study, we employed a hydrothermal method to synthesize NiMoWOX microrods (NiMoWOX@NF). Subsequently, an annealing process yielded a composite N-doped carbon-coated Ni3N/MoO2/WO2 nanorods (NC@Ni3N/MoO2/WO2@NF), preserving the ultrahigh-specific surface area of the original structure. A two-electrode electrolytic cell was assembled using NC@Ni3N/MoO2/WO2@NF as the cathode and NiMoWOX@NF as the anode, demonstrating exceptional performance in seawater splitting. The cell operated at a voltage of 1.51 V with a current density of 100 mA·cm−2 in an alkaline seawater solution. Furthermore, the NC@Ni3N/MoO2/WO2@NF || NiMoWOX@NF electrolytic cell exhibited remarkable stability, running continuously for over 120 h at a current of 1100 mA·cm−2 without any observable delay. These experimental results are corroborated by density functional theory calculations. The NC@Ni3N/MoO2/WO2@NF || NiMoWOX@NF electrolyzer emerges as a promising option for industrial-scale hydrogen production through seawater electrolysis.

Crystalline metal phosphide-coated amorphous iron oxide-hydroxide (FeOOH) with oxygen vacancies as highly active and stable oxygen evolution catalyst in alkaline seawater at high current density

In this study, we employed a straightforward phosphorylation approach to achieve a dual objective: constructing c-a heterostructures consisting of crystalline Ni12P5 and amorphous FeOOH, while simultaneously enhancing oxygen vacancies. The resulting oxygen evolution reaction (OER) catalyst, Ni12P5/FeOOH/NF, exhibited remarkable performance with current densities of 500 mA cm−2 in both 1 M KOH and 1 M KOH + seawater, requiring low overpotentials of only 288 and 365 mV, respectively. Furthermore, Ni12P5/FeOOH/NF exhibited only a slight increase in overpotential, with increments of 18 mV and 70 mV in 1 M KOH after 15 and 150 h, and 32 mV and 108 mV in 1 M KOH + seawater at 500 mA cm−2 after 15 and 150 h, respectively. This minimal change can be attributed to the stabilized c-a structure, the protective coating of Ni12P5, and superhydrophilic. Through in-situ Raman and ex-situ XPS analysis, we discovered that Ni12P5/FeOOH/NF can undergo a reconfiguration into an oxygen vacancy-rich (Fe/Ni)OOH phase during OER process. The elevated OER activity is mainly due to the contribution of the oxygen vacancy-rich (Fe/Ni)OOH phase from the reconfigure of the Ni12P5/FeOOH/NF. This finding emphasizes the critical role of oxygen vacancies in facilitating the production of OO species and overcoming the limitations associated with OOH formation, ultimately enhancing the kinetics of the OER.

Unraveling the Tandem Effect of Nitrogen Configuration Promoting Oxygen Reduction Reaction in Alkaline Seawater

AbstractDeveloping seawater‐based high‐performance oxygen reduction reaction (ORR) electrocatalysts is meaningful to renewable energy storage and conversion, and the Fe‐based derivatives encapsulated by nitrogen (N) doped carbon are the typical representative. Nevertheless, unrevealing the mechanism of N configuration to ORR activity and chlorine resistance is still a great challenge. In this work, a feasible strategy is developed to prepare controllable pyridinic/pyrrolic‐N doped carbon‐coated Fe‐based electrocatalysts (FexN‐NC). Drawing support from the H3PO4 blocking based in situ Fourier transform infrared spectroscopy (FTIR) test and density‐functional theory (DFT) calculation, the tandem effect of pyridinic‐N and pyrrolic‐N on ORR is proved. Additionally, the low hydrogen peroxide (H2O2) yield and 4e− pathway of FexN‐NC demonstrate that N doping effectively reduces the adsorption of Cl−, which is consistent with the low Cl− adsorption energy of DFT. The half‐wave potential (E1/2) of FexN‐NC for ORR reaches 0.874 V in alkaline seawater, and ZABs assembled with FexN‐NC as the air cathode deliver a remarkable power density (162 mW cm−2), along with excellent long‐term durability (>400 h).

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core–shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core–shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm−2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm−2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

Self-sustaining alkaline seawater electrolysis via forward osmosis membranes

Seawater electrolysis for hydrogen production faces inherent challenges, including side reactions, corrosion, and scaling, stemming from the intricate composition of seawater. In response, researchers have turned to continuous water splitting using forward osmosis (FO)-driven seawater desalination. However, the necessity of a neutral electrolyte hampers this strategy due to the limited current density and scarcity of precious metals. Herein, this study applies alkali-durable FO membranes to enable self-sustaining seawater splitting, which can selective withdraw water molecules, from seawater, via concentration gradient. The membranes demonstrated outstanding perm-selectivity of water/ions (∼5830 mol mol−1) during month-long alkaline resistance tests, preventing electrolyte leaching (>97% OH− retention) while maintaining ∼95% water balance (VFO = Velectrolysis) via preserved concentration gradient for consistent forward-osmosis influx of water molecules. With the consistent electrolyte environment protected by the polyamide FO membranes, the NiFe-Ar-P catalyst exhibits promising performance: a sustain current density of 360 mA cm−2 maintained at the cell voltage of 2.10 V and 2.15 V for 360 h in the offshore seawater, preventing Cl/Br corrosion (98% rejection) and Mg/Ca passivation (99.6% rejection). This research marks a significant advancement towards efficient and durable seawater-based hydrogen production.

Electron Redistribution of Ru Site on MoO2@NiMoO4 Support for Efficient Ampere-Level Current Density Electrolysis of Alkaline Seawater.

Seawater electrolysis is a promising but challenging strategy to generate carbon-neutral hydrogen. A grand challenge for hydrogen evolution reaction (HER) from alkaline seawater electrolysis is the development of efficient and stable electrocatalysts to overcome the limitation of sluggish kinetics. Here, a 3D nanorod hybrid catalyst is reported, which comprises heterostructure MoO2@NiMoO4 supported Ru nanoparticles (Ru/ MoO2@NiMoO4) with a size of ≈5nm. Benefitting from the effect of strongly coupled interaction, Ru/MoO2@NiMoO4 catalyst exhibits a remarkable alkaline seawater hydrogen evolution performance, featured by a low overpotential of 184mV at a current density of 1.0 A cm-2, superior to commercial Pt/C (338mV). Experimental observations demonstrate that the heterostructure MoO2@NiMoO4 as an electron-accepting support makes the electron transfer from the Ru nanoparticles to MoO2, and thereby implements the electron redistribution of Ru site. Mechanistic analysis elucidates that the electron redistribution of active Ru site enhances the ability of hydrogen desorption, thereby promoting alkaline seawater HER kinetics and finally leading to a satisfactory catalysis performance at ampere-level current density of alkaline seawater electrolysis.

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.

Manipulating electronic structure of nickel phosphide via asymmetric coordination interaction for anion-exchange membrane based seawater electrolysis

Alkaline seawater electrolysis faces serious problems such as low catalytic activity of bifunctional catalysts and vulnerability to Cl- corrosion. Hence, Ru-doped nickel phosphide asymmetric structure (Ru-Ni2P/Ni5P4) has been synthesized as highly efficient and corrosion resistant electrocatalysts for alkaline seawater electrolysis at high current density. In-situ characterization technique and DFT calculations reveal that compared with the monophase nickel phosphide, the construction of NixP asymmetric structure manipulate the electronic structure and d-band center, promoting the adsorption of intermediates, as well as accelerate phase transition of the OER process. Moreover, the weak adsorption energy of Cl- on the surface of the Ru-Ni2P/Ni5P4 catalyst avoids the corrosion of Cl- in seawater. Consequently, Ru-Ni2P/Ni5P4 achieve 1000 mA cm−2 with overpotentials of only 128 and 450 mV for HER and OER, respectively. After assembling the Anion-exchange-membrane water electrolyzer (AEMWE), Ru-Ni2P/Ni5P4 shows high average efficiency and economic value at different current densities, and demonstrates its corrosion resistance to Cl- and potential for industrial applications.

Controlled synthesis of Co3O4@CoP heterostructured nanoarrays as efficient electrocatalysts in alkaline seawater and urea

How to prepare clean energy has always been a problem to be solved by the modern green chemical industry. Compared with the electrolysis of water to produce hydrogen, electrolysis of seawater for raw material requirements are lower and more widely used. However, the lacks of maturity of the technology, the high cost and the generation of harmful gases such as chlorine in the electrocatalytic process have hindered the development of this process. This study demonstrates a construction of heterogeneous structure based on Co ions as an efficient multifunctional catalyst for overall seawater splitting and urea oxidation. This hybrid structure can combine nanosheets and nanowires, thus exposing the catalyst to more active sites and shortening the ion diffusion path. Comparing the hybrid structure with the single structure, Co3O4@CoP exhibits excellent multifunctional catalytic activity in alkaline seawater and urea. In the oxygen evolution reaction, the working potential is only 1.60 V and 1.70 V at a current density of 50 mA/cm2 and 100 mA/cm2. And in the hydrogen evolution reaction, the working potential was only −0.16 V at a current density of −10 mA/cm2, demonstrating excellent bifunctional activity. On this basis, the catalyst also demonstrated excellent activity for urea oxidation reaction in alkaline environment, with an operating potential of only 1.28 V at a current density of 10 mA/cm2. And the durability of this catalyst is good, it can keep 5 mA/cm2 for 12 h under the constant voltage of 1.45 V, but the initial potential falls off too fast, and there is a decline in performance, which is closely related to the corrosion of Cl- present in seawater. It was shown by density functional theory (DFT) that hierarchical nanostructures can increase the transfer rate of reaction intermediates and the water adsorption energy. At the end of this study, by comparing single nanostructures with hybrid nanostructures, it can be reasonably conjectured that the accompanying increase in the number the heterostructure is resistant to Cl- corrosion in seawater.

Metallic Cu-incorporated NiFe layered double hydroxide nanosheets enabling energy-saving hydrogen generation from chlorine-free seawater electrolysis coupled with sulfion upcycling

Development of multifunctional non-noble electrocatalysts for seawater electrolysis is imperative but still challenging for scale-up hydrogen production to avoid harmful chlorine chemistry. Herein, the metallic Cu-incorporated NiFe layered double hydroxide (LDH) nanosheets are prepared by a facile consecutive corrosion strategy using iron foam (IF) as a reactive substrate, which enable the corrosion-resistant and chlorine-free seawater electrolysis combined with anodic sulfion oxidation for energy-efficient hydrogen production at ultralow electricity consumption. The NiFe-LDH/Cu-IF exhibits excellent electrocatalytic activities for hydrogen evolution reaction (HER) and sulfion oxidation reaction (SOR), achieving low potentials of 0.203 and 0.310 V (vs RHE) at 100 mA cm−2 in alkaline seawater, respectively. The assembled hybrid HER||SOR seawater electrolyzer realizes the ultra-low cell voltage of 0.619 V and power consumption of 1.48 kWh/m3 H2 at 50 mA cm−2, cutting energy consumption over 67 % compared to conventional seawater electrolysis.

Constructing Amorphous-Crystalline Interfacial Bifunctional Site Island-Sea Synergy by Morphology Engineering Boosts Alkaline Seawater Hydrogen Evolution.

The development of efficient and durable non-precious hydrogen evolution reaction (HER) catalysts for scaling up alkaline water/seawater electrolysis is highly desirable but challenging. Amorphous-crystalline (A-C) heterostructures have garnered attention due to their unusual atomic arrangements at hetero-interfaces, highly exposed active sites, and excellent stability. Here, a heterogeneous synthesis strategy for constructing A-C non-homogeneous interfacial centers of electrocatalysts on nanocages is presented. Isolated PdCo clusters on nanoscale islands in conjunction with Co3S4 A-C, functioning as a bifunctional site "island-sea" synergy, enable the dynamic confinement design of metal active atoms, resulting in excellent HER catalytic activity and durability. The hierarchical structure of hollow porous nanocages and nanoclusters, along with their large surface area and multi-dimensional A-C boundaries and defects, provides the catalyst with abundant active centers. Theoretical calculations demonstrate that the combination of PdCo and Co3S4 regulates the redistribution of interface electrons effectively, promoting the sluggish water-dissociation kinetics at the cluster Co sites. Additionally, PdCo-Co3S4heterostructure nanocages exhibit outstanding HER activity in alkaline seawater and long-term stability for 100h, which can be powered by commercial silicon solar cells. This finding significantly advances the development of alkaline seawater electrolysis for large-scale hydrogen production.

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.

Anionic phosphorous and sulfur regulate self-supported Ni-Fe-based electrocatalyst for water-splitting under large current density

Nickel-iron based (Ni-Fe) catalysts are widely used in the electrolysis of water due to their high activity and low cost. However, the development of highly active non-precious metal catalysts is still a great challenge. Herein, self-supported nickel–iron phosphide is fabricated through a sulfurization/phosphorization approach (Ni-Fe-P-S-1/Ni-Fe-P-S-2). The prepared catalysts show excellent catalytic performance and stability. The HER performance of Ni-Fe-P-S-1 reaches 500 mA cm−2 with small overpotentials of 289 mV in alkaline freshwater. Meanwhile, the Ni-Fe-P-S-2 requires 312 and 375 mV to reach 500 mA cm−2 in alkaline freshwater and alkaline seawater for OER. Remarkably, at the current density of 500 mA cm−2, the Ni-Fe-P-S-1||Ni-Fe-P-S-2 electrolyzer requires only 1.85 V in alkaline. Interestingly, sustainable energies can power the electrolyzer effectively. The work provides methods for potentially promising and cost-effective electrocatalysts.

Multiscale modulation of ultra-small ruthenium anchored on bimetallic sulfides for seawater electrolysis at ampere-level current density

Developing efficient and stable electrocatalysts is the critical challenge for hydrogen evolution reaction (HER) from seawater electrolysis. The design of catalysts for seawater HER needs to consider not only high intrinsic activity determined by the electronic structure, but also favorable mass transfer at the catalyst's surface. Herein, a unique nanoarray hybrid heterojunction consisting of ultra-small Ru nanoparticle (NPs) decorated on the surface of NiMo bimetallic sulfides (NiMoSx) is proposed. This Ru/NiMoSx heterostructure delivers an ampere-level current density of 1.0 A cm−2 at an overpotential of only 208 mV in alkaline seawater, which is far superior to the performance of commercial Pt/C. In situ spectroscopy and electronic structural analysis demonstrate that the atom-level synergy between Ru NPs and NiMoSx heterostructure makes the electron transfer from Ru to Ni/Mo, weakening the interaction of Ru and H atom, eventually facilitating the H desorption. Also, the results of contact angle tests and simulation calculations reveal that the micro-level modulation of nanoarray structure favors the diffusion of electrolyte and bubble, ensuring rapid mass transfer and exposing multiple active sites. With the multiscale modulation including optimized electronic structure and fast mass transfer, both H2 generation and transportation for Ru/NiMoSx are all prompted, thus leading to outstanding seawater HER performance.

Dynamic chloride ion adsorption on single iridium atom boosts seawater oxidation catalysis

Seawater electrolysis offers a renewable, scalable, and economic means for green hydrogen production. However, anode corrosion by Cl- pose great challenges for its commercialization. Herein, different from conventional catalysts designed to repel Cl- adsorption, we develop an atomic Ir catalyst on cobalt iron layered double hydroxide (Ir/CoFe-LDH) to tailor Cl- adsorption and modulate the electronic structure of the Ir active center, thereby establishing a unique Ir-OH/Cl coordination for alkaline seawater electrolysis. Operando characterizations and theoretical calculations unveil the pivotal role of this coordination state to lower OER activation energy by a factor of 1.93. The Ir/CoFe-LDH exhibits a remarkable oxygen evolution reaction activity (202 mV overpotential and TOF = 7.46 O2 s−1) in 6 M NaOH+2.8 M NaCl, superior over Cl--free 6 M NaOH electrolyte (236 mV overpotential and TOF = 1.05 O2 s−1), with 100% catalytic selectivity and stability at high current densities (400-800 mA cm−2) for more than 1,000 h.

Arming Amorphous NiMoO4 on Nickel Phosphide Enables Highly Stable Alkaline Seawater Oxidation.

Seawater electrolysis holds tremendous promise for the generation of green hydrogen (H2). However, the system of seawater-to-H2 faces significant hurdles, primarily due to the corrosive effects of chlorine compounds, which can cause severe anodic deterioration. Here, a nickel phosphide nanosheet array with amorphous NiMoO4 layer on Ni foam (Ni2P@NiMoO4/NF) is reported as a highly efficient and stable electrocatalyst for oxygen evolution reaction (OER) in alkaline seawater. Such Ni2P@NiMoO4/NF requires overpotentials of just 343 and 370mV to achieve industrial-level current densities of 500 and 1000mA cm-2, respectively, surpassing that of Ni2P/NF (470 and 555mV). Furthermore, it maintains consistent electrolysis for over 500h, a significant improvement compared to that of Ni2P/NF (120h) and Ni(OH)2/NF (65h). Electrochemical in situ Raman spectroscopy, stability testing, and chloride extraction analysis reveal that is situ formed MoO4 2-/PO4 3- from Ni2P@NiMoO4 during the OER test to the electrode surface, thus effectively repelling Cl- and hindering the formation of harmful ClO-.

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.

Construction of Heterojunction-Rich Metal Nitrides Porous Nanosheets Electrocatalyst for Alkaline Water/Seawater Splitting at Large Current Density.

The exploiting electrocatalysts for water/seawater electrolysis with remarkable activity and outstanding durability at industrial grade current density remains a huge challenge. Herein, CoMoNx and Fe-doped CoMoNx nanosheet arrays are in-situ grown on Ni foam, which possess plentiful holes, multilevel heterostructure, and lavish Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF interfaces. They require low overpotentials of 213 and 296mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline media to achieve current density of 800mA cm-2, respectively, and both possess low Tafel slopes (51.1 and 49.1mV dec-1) and undiminished stability over 80h. Moreover, the coupled Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF electrolyzer requires low voltages of 1.735V to yield 500mA cm-2 in alkaline water. Notably, they also exhibit exceptional electrocatalytic properties in alkaline seawater (1.833 V@500mA cm-2). The experimental studies and theoretical calculations verify that Fe doping does reduce the energy barrier from OH* to O* intermediates during OER process after catalyst reconstruction, and the non-metallic N site from MoN exhibits the lowest theoretical overpotential. The splendid catalytic performance is attributed to the optimized local electron configuration and porous structure. This discovery provides a new design method toward low-cost and excellent catalysts for water/seawater splitting to produce hydrogen.

Multi-dimensional MoS2/S-doped-CoP heterostructure nanoarrays as an efficient electrocatalyst for hydrogen evolution reaction

Developing efficient and economical electrocatalysts for hydrogen evolution reaction (HER) over a broad pH range has received considerable attention. In this work, we prepared multi-dimensional MoS2/S-CoP heterojunction catalysts by utilizing the carbon clothes supported ZIF-67 array as templates combining with Mo-ion exchange and high-temperature phosphorization-sulfidation strategy. The introduction of MoS2 into S-CoP results in electron redistribution and the formation of a distinctive space charge region at the two-phase contact interface, thereby effectively tuning surface properties, enhancing electron conductivity, and improving electrocatalytic activity. According to Density Functional Theory (DFT) calculations, the introduction of MoS2 is advantageous for the adsorption and desorption of H*, resulting in the value of ΔGH* very close to zero. Furthermore, the adsorbed water molecules are more readily activated, rendering the ΔGH2O-dis decrease, thus significantly promoting HER activity. These features contribute to robust HER electrocatalytic performance in a wide pH range and even in seawater, which is also beneficial for industrial applications. In particular, MoS2/S-CoP exhibits superior HER performance in alkaline seawater, requiring only 197 and 228 mV to reach the current densities of 100 and 200 mA cm-2, respectively. This study offers novel perspectives on high-performance heterostructures for HER electrocatalysts in alkaline seawater environments.