Efficient Electrocatalytic Water Splitting Research Articles

La-exacerbated lattice distortion of high entropy alloys for enhanced electrocatalytic water splitting

The complex active site configurations of high entropy alloys (HEAs) limit their performance optimization and wide applications. Herein, we report a FeCoNiMnRuLa/CNT catalyst for efficient electrocatalytic water splitting by introducing La to break the lattice ordering of FeCoNiMnRu. The introduction of La reduces the number of unpaired electrons in FeCoNiMnRu, which in turn accelerates the transition of singlet state oxygen-containing intermediate to triplet state oxygen. The DFT results verify that the lattice distortion exacerbated by La alters the d-orbital electronic configuration of FeCoNiMnRu, so that Fe and Ni play an important role in the critical adsorption of *OH in the OER as well as *H2O in the HER, and Ru, Co, and Mn provide a strong safeguard for the desorption of oxygen-containing intermediates, thereby retaining excellent activity and stability during water decomposition. Our work showcases that the incorporation of rare earth elements opens new opportunities to improve the performance of HEAs.

Electrocatalyst‐Hydrogel Polymer Nanocomposite Thin Films for Water Splitting

AbstractRealization of scalable technologies for key processes like electrochemical water splitting requires the development of sustainable, efficient and cost‐effective catalytic electrodes. The innumerable electrocatalysts being developed in contemporary research rely on the use of a limited choice of binders for effective deployment in the electrolysis setting. Recent studies have demonstrated the utility of electrically insulating hydrogel polymers as suitable matrices for incorporating the electrocatalyst nanoparticles; the nanocomposite thin films coated on conducting substrates mediate highly efficient electrocatalytic water splitting reactions through the effective confinement of the electrolyte within and release of the gaseous products. After a brief introduction to the basic challenges in the field and the existing approaches that address them, this article outlines the promise of hydrogel based nanocomposite thin films in developing efficient and sustainable catalytic electrodes for water splitting, and their functional role in enhancing the efficiency of the electrochemical process. Directions for further development in this domain are noted.

Nitrogen-phosphorus co-doped carbon layer-confined cobalt phosphide-anchored nickel molybdate heterojunctions for efficient electrocatalytic overall water splitting

Aiming at the problems of low catalytic activity and poor stability of nickel molybdate-based catalysts. Herein, we successfully prepared nitrogen and phosphorus co-doped carbon (NPC) layer-confined cobalt phosphide (CoP)-anchored nano-cuboid nickel molybdate (NNM) catalysts (NNM-CoP@NPC/NF) on nickel foam (NF) by hydrothermal and phosphating methods. The strong interaction between CoP and NNM is verified by experimental characterization and theoretical calculation, which improves the electronic structure of NNM and reduces the orbital energy of the central anti-bond, thus optimizing the adsorption and desorption of reaction intermediates/products. NiOOH and MoO42− formed by reforming the catalyst under the action of NPC-confined layer maintain catalytic activity and stability in cooperation with CoP and NPC, respectively. Accordingly, in the assembled two-electrode system NNM-CoP@NPC/NF, the cell voltage of only 1.51 V is needed to drive a current density of 10 mA cm−2. More importantly, the current density remained at 100 mA cm−2 for 100 h under the voltage of 1.66 V with almost no attenuation. This strategy of constructing interface regulation and confinement provides a new insight for improving the activity and stability of water splitting in alkaline media.

Cobalt nanoparticles intercalation coupled with tellurium-doping MXene for efficient electrocatalytic water splitting

Nowadays, the inherent re-stacking nature and weak d-p hybridization orbital interactions within MXene remains significant challenges in the field of electrocatalytic water splitting, leading to unsatisfactory electrocatalytic activity and cycling stability. Herein, this work aims to address these challenges and improve electrocatalytic performance by utilizing cobalt nanoparticles intercalation coupled with enhanced π-donation effect. Specifically, cobalt nanoparticles are integrated into V2C MXene nanosheets to mitigate the re-stacking issue. Meanwhile, a notable charge redistribution from cobalt to vanadium elevates orbital levels, reduces π*-antibonding orbital occupancy and alleviates Jahn-Teller distortion. Doping with tellurium induces localized electric field rearrangement resulting from the changes in electron cloud density. As a result, Co-V2C MXene-Te acquires desirable activity for hydrogen evolution reaction and oxygen evolution reaction with the overpotential of 80.8 mV and 287.7 mV, respectively, at the current density of −10 mA cm−2 and 10 mA cm−2. The overall water splitting device achieves an impressive low cell voltage requirement of 1.51 V to obtain 10 mA cm−2. Overall, this work could offer a promising solution when facing the re-stacking issue and weak d-p hybridization orbital interactions of MXene, furnishing a high-performance electrocatalyst with favorable electrocatalytic activity and cycling stability.

Co(OH)2 confined in MIL-100 nanosheets with enriched oxygen vacancies for efficient electrocatalytic water splitting

Exploring cost-effective and advanced bifunctional electrocatalysts is crucial for overall water splitting. Confinement engineering integrates electronic structure and interface transfer for synergistic cooperation between active sites and carriers, thus realizing enhanced electrocatalytic performance. Herein, Co(OH)2 confined MIL-100 nanosheets are grown on nickel foam (Co(OH)2/MIL-100) by cobalt acetate colloid. The confinement effect guarantees the highly dispersed Co(OH)2 in MIL-100. The two-dimensional nanosheet arrays of Co(OH)2/MIL-100 provide sufficient active sites and rich channels for facilitated ion/electron transportation. The characterizations and theoretical calculation prove that the strong coupling between Co(OH)2 and MIL-100 induces oxygen vacancies and highly active Fe3+ species to promote charge transfer and regulate the d-band center. As a result, the intermediate adsorption strength is optimized, which is beneficial to boost the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) process. The Co(OH)2/MIL-100 exhibits competitive OER and HER overpotentials of 260 mV and 160 mV at 50 mA cm−2 in alkaline electrolyte, respectively. Furthermore, the two-electrode electrolyzer equipped with Co(OH)2/MIL-100(+) || Co(OH)2/MIL-100(-) displays a low operation potential of 1.62 V (50 mA cm−2) and maintains high stability for 20 h. Thus, this work offers a novel colloid-assisted confinement strategy to simultaneously tailor the electronic structure and active sites for highly efficient electrocatalysts.

One-step electrodeposition of bifunctional MnCoPi electrocatalysts with wrinkled globular-flowers-like structure for highly efficient electrocatalytic water splitting

The development and exploration of electrocatalysts with the high reactive and abundant availability is still extremely crucial in electrocatalytic overall water splitting. Herein, a novel globular-flowers-like MnO2/Co3(PO4)2 (denoted as MnCoPi) electrocatalyst on nickel foam was successfully prepared through a simple one-step electrodeposition method. The MnCoPi electrocatalyst simultaneously delivers remarkable electrocatalytic activities for hydrogen evolution reaction (HER) with overpotentials (η10) reaching 102 mV and oxygen evolution reaction (OER) with overpotentials (η10) up to 225 mV in 1 M KOH solution. Furthermore, the assembled electrolyzer cell utilizing MnCoPi as the cathode and anode only requires a low voltage of 1.55 V to achieve a current density of 10 mA cm−2. Moreover, the developed MnCoPi electrocatalyst shows excellent stability during continuous operation for 48 h in OER, HER and overall water splitting process. Compared with the pristine MnO2, the significant electrocatalytic properties of MnCoPi can mainly be attributed to the improved physicochemical properties such as distinctive globular-flowers-like morphology, huge specific surface areas and abundant porosity structure, low electrochemical resistance, especially for the formed heterojunction between MnO2 and Co3(PO4)2, which can provide abundant reactive sites and accelerated electron transfer, etc. Consequently, this work provides a new avenue for the development of efficient and stable bifunctional electrocatalysts for overall water splitting.

Synergistic dual built-in electric fields in 1T-MoS2/Ni3S2/LDH for efficient electrocatalytic overall water splitting reactions

Designing cost-effective electrocatalysts for water decomposition is crucial for achieving environmental-friendly hydrogen production. A transition metal sulfide/hydroxide electrocatalyst (1T-MoS2/Ni3S2/LDH) with double heterogeneous interfaces was developed through a two-step hydrothermal assisted electrodeposition method. The presence of the two built-in electric fields not only accelerated the charge transfer at the interface, but also enhanced the adsorption of the reactants and intermediate groups, and therefore improved the reaction rate and overall catalytic performance. The results suggest that the 1T-MoS2/Ni3S2/LDH catalysts display exceptional electrocatalytic reactivity. Under alkaline conditions, the overpotential of the electrocatalyst was 187 (η50) mV for OER and 104 (η10) mV for HER. Furthermore, the two-electrode system assembled by the electrocatalyst needs only a voltage of 1.55 V to deliver a current density of 10 mA cm−2. Our result provides a simple and effective methodical approach to the design of dual heterogeneous interfacial electrocatalysts.

Tunable decoration of Ni/Ni3N nano-heterostructures on N-defective g-C3N4 via topochemical self-nitridation for efficient electrocatalytic overall water splitting

The growth of base-metal-based heterostructures on metal-free carriers is considered an effective strategy for designing low-cost high-efficiency hybrid electrocatalysts with electronic modulation for bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as further overall water splitting (OWS). Herein, Ni/Ni3N heterostructures with regulable composition are grown in-situ on N-defective graphitic carbon nitride (g-C3N4) through a novel ammonia-free topochemical self-nitridation route. Benefitting from the synergetic effect between Ni/Ni3N heterointerface and the strong support of g-C3N4 carrier, the as-fabricated Ni/Ni3N/g-C3N4 composite performs superior capacity toward both HER and OER in alkaline conditions. The optimal Ni/Ni3N/g-C3N4 sample requires low overpotentials for HER (55 mV) and OER (253 mV) to drive a current density of 10 mA cm−2, along with long-term durability. Furthermore, the constructed Ni/Ni3N/g-C3N4 (+||−) electrolytic cell for alkaline OWS can afford a current density of 10 mA cm−2 under a voltage of 1.556 V with outstanding stability.

Ion-exchange strategy for fabricating highly dispersed Co–MoS2 on N-doped graphene for efficient bifunctional electrocatalytic water splitting

Recently, the pivotal to electrocatalytic water splitting is developing efficient and earth-abundant electrocatalysts to accelerate the sluggish kinetics of hydrogen and oxygen evolution reactions (HER and OER). In this work, (NH4)2MoS4 derived from polyoxometalates ((NH4)6Mo7O24·4H2O) were immobilized onto the ion exchange resin D314, and highly dispersed Co-molybdenum disulfide (Co–MoS2@NG-4) on nitrogen-doped graphene catalyst was prepared. The optimized Co–MoS2@NG-4 shows excellent electrocatalytic performance for HER and OER. Specifically, the low overpotentials of 202 and 352 mV are required to drive the current density of 10 mA cm−2 with the small Tafel slope of 77.30 and 153.50 mV dec−1 for HER and OER, respectively. The Co–MoS2@NG-4 demonstrates excellent stability, maintaining a robust operation for 5000 cyclic tests with no detectable stability decay.

Phytic acid treated nickel–iron hydroxide promotes efficient electrocatalytic overall water splitting

Phytic acid-treated NiFe-LDH exposes more active sites and can improve the electrocatalytic performance in water splitting.

Non-noble metal coordinated hypercrosslinked polymers based on porphyrin for efficient electrocatalytic OER

Electrochemical catalysts for the oxygen evolution reaction (OER) with abundant reserves, high catalytic activity, and robust stability are highly crucial for efficient electrocatalytic water splitting.

Regulating catalytic kinetics in nanoclimbing-wall-like NiO/NiCoP hybrids for enhanced overall water splitting

Developing integrated cost-efficient bifunctional electrocatalysts with unique architecture comparable to noble metal is greatly desirable for efficient electrocatalytic water splitting. Herein, a highly active NiO/NiCoP hybrid catalyst on nickel foam...

Eco-friendly mixed metal (Mg–Ni) ferrite nanosheets for efficient electrocatalytic water splitting

Eco-friendly and cost-effective catalysts with multiple active sites, large surface area, high stability and catalytic activity are highly desired for efficient water splitting as a sustainable green energy source. Within this line, a facile synthetic approach based on solventless thermolysis was employed for the simple and tunable synthesis of Ni1−xMgxFe2O4 (0 ≤ x ≤ 1) nanosheets. The characterization of nanosheets (via p-XRD, EDX, SEM, TEM, HRTEM, and SAED) revealed that the pristine ferrites (NiFe2O4 and MgFe2O4), and their solid solutions maintain the same cubic symmetry throughout the composition regulation. Elucidation of the electrochemical performance of the nanoferrite solid solutions showed that by tuning the local chemical environment of Ni in NiFe2O4 via Mg substitution, the intrinsic catalytic activity was enhanced. Evidently, the optimized Ni0.4Mg0.6Fe2O4 catalyst showed drastically enhanced HER activity with a much lower overpotential of 121 mV compared to the pristine NiFe2O4 catalyst. Moreover, Ni0.2Mg0.8Fe2O4 catalyst exhibited the best OER performance with a low overpotential of 284 mV at 10 mA/cm2 in 1 M KOH. This enhanced electrocatalytic activity could be due to improved electronic conductivity caused by the partial substitution of Ni2+ by Mg2+ in the NiFe2O4 matrix as well as the synergistic effect in the Mg-substituted NiFe2O4. Our results suggest a feasible route for developing earth-abundant metal oxide-based electrocatalysts for future water electrolysis applications.

Nitriding-reduction fabrication of coralloid CoN/Ni/NiO for efficient electrocatalytic overall water splitting

The introduction of nitride in Ni/NiO-based catalytic system for electrocatalystic water splitting via a skillful strategy remains a great challenge. Herein, we proposed a one-step urea nitriding-reduction strategy for the fabrication of novel CoN/Ni/NiO electrocatalyst on carbon cloth (CC). The combination of CoN and Ni/NiO could construct CoN/Ni interface and expose more active sites, thus exhibiting excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in alkaline media. Consequently, CoN/Ni/NiO catalyst exhibited remarkable HER/OER performance with an overpotential of 92 mV/114 mV at 10 mA cm−2 in 1.0 M KOH, along with a low cell voltage of 1.56 V to enhance overall water splitting. In addition, when CoN was introduced in Ni/NiO system, CoN/Ni/NiO displayed high conductivity, large active surface areas, high Faradic efficiency (FE) and remarkable stability. Density functional theory (DFT) calculations demonstrated that CoN/Ni/NiO possessed a decreased d-band center beneficial for optimizing the energy barrier of intermediates. Specifically, the ΔGH2O (0.088 eV) and ΔGH* (0.18 eV) in HER and the ΔGOOH* (1.4 eV) of rate determining step (O*→OOH*) in OER of CoN/Ni/NiO catalyst were optimized to achieve high water splitting activity. Simultaneously, for adsorbed H2O on CoN/Ni/NiO, the OH bond length extended from 0.975 to 1.110 Å, and the bond angle enlarged from 104.271 to 109.471°, thereby directly demonstrating the excellent HER/OER performance of CoN/Ni/NiO.

Synergistic Activation of Inert Iron Oxide Basal Planes through Heterostructure Formation and Doping for Efficient Hydrogen Evolution.

Iron oxides have emerged as a very promising and cost-effective alternative to precious metal catalysts for hydrogen production. However, the inert basal plane of iron oxides needs to be activated to enhance their catalytic efficiency. In this study, we employed heterostructure engineering and doped nickel to cooperatively activate the basal planes of iron oxide (Ni-Fe2 O3 /CeO2 HSs) to achieve high hydrogen evolution reaction (HER) activity. The Ni-Fe2 O3 /CeO2 HSs electrocatalyst demonstrates excellent basic HER activity and stability, such as an extremely low overpotential of 43 mV at 10 mA cm-2 current density and corresponding Tafel slope of 58.6 mV dec-1 . The increase in electrocatalyst activity and acceleration of hydrogen precipitation kinetics arises from the dual modulation of Ni doping and heterostructure, which not only modulates the electrocatalyst's electronic structure, but also increases the number and exposure of active sites. Remarkably, the generation of heterogeneous structure makes the catalyst se. The Ni-doped catalyst has not only increased HER activity but also low-temperature resistance. These results suggest that the synergistic activation of inert iron oxide basal planes through heterostructure formation and doping is a feasible strategy. Furthermore, for efficient electrocatalytic water splitting, this technique can be extended to other non-noble metal oxides.

Efficient electrocatalytic overall water splitting of porous 3D CoPt3/a-FCWO-NS heterostructures: Morphology modulation and interfacial engineering for the formation of crystalline-amorphous nanosheets

Achieving efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) simultaneously in the electrocatalytic water-splitting is essential to achieve a green hydrogen economy. However, a rational catalyst design still faces great challenges due to the slow kinetic limitations such as electron transfer at the electrode-electrolyte interface. Herein, a porous 3D CoPt3/a-FCWO-NS heterostructures was formed by morphology modulation and interfacial engineering. Notably, the catalyst requires only 1.51 V to achieve 10 mA cm−2 in 1 M KOH, and a commercial 1.5 V cell can drive the overall water-splitting with excellent stability. DFT combined with XPS results reveal the electron transfer between CoPt3 and FeCoW oxides. Due to the ensemble effect CoPt3 exhibits an electron deficient state moderating the slow kinetics of the OER process. Furthermore, the substrate FeCoW oxides modulates the d-band position of CoPt3, and the suitable adsorption energy for hydrogen-containing intermediates makes CoPt3/a-FCWO favorable for the HER process.

Non-covalent interaction of atomically dispersed dual-site catalysts featuring Co and Ni nascent pair sites for efficient electrocatalytic overall water splitting

The scarcity of highly effective and economical catalysts is a major impediment to the widespread adoption of electrochemical water splitting for the generation of hydrogen. MoS2, a low-cost candidate, suffers from inefficient catalytic activity. Nonetheless, a captivating strategy has emerged, which involves the engineering of heteroatom doping to enhance electrochemical proficiency. This investigation demonstrates a successful implementation of the strategy by combining ultrathin MoS2 nanosheets with Co and Ni dual single multi-atoms (DSMAs) grown directly on 2D N-doped carbon nanosheets (CoNi-MoS2/NCNs) for the purpose of improving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). With the aid of a dual-atom doped bifunctional electrocatalyst, effective water splitting has been achieved across a broad pH range in electrolytes. The double doping of Co and Ni strengthens their interactions, thereby altering the electromagnetic composition of the host MoS2 and ultimately leading to improved electrocatalytic activity. Additionally, the synergistic effect between NCNs and MoS2 nanosheets provided efficient electron transport channels for ions and an ample surface area with open voids for ion diffusion. Consequently, the CoNi-MoS2/NCNs catalysts demonstrated exceptional stability and activity, producing low degree overpotentials of 180.5, 124.9, and 196.4 mV for HER and 200, 203, and 207 mV for OER in neutral, alkaline, and acidic mediums, respectively, while also exhibiting outstanding overall water-splitting performance, durability, and stability when used as an electrolyzer at universal pH.

Solvothermally designed Pr-MOF/Fe2O3 based nanocomposites for efficient electrocatalytic water splitting

To meet the energy demand of modern civilization, efforts to find renewable, safe, and highly effective fuel generation are still a big challenge. The oxygen evolution reaction (OER) is one of many modern technologies for hydrogen generation, and a number of new electrode materials have been created to increase the effectiveness of O2 evolution. This project utilizes a range of high performance nanomaterials, such as Pr-MOF, Fe2O3, and Pr-MOF/Fe2O3, to carry out the oxygen evolution reaction. This study shows that Pr-MOF/Fe2O3 exhibits exceptional electrocatalytic activity in alkaline solution with 238 mV overpotential at the current density of 10 mA cm−2 and a Tafel slope of 37 mV dec−1 which is much lower when compared to pure Pr-MOF and Fe2O3. The enhanced electrochemical results are due to the higher electrochemical surface area of 237 cm2. This work will lay the foundation for an approach to enhance the crystalline nature of surface-active nanoparticles made from rare earth MOFs for a range of electrochemical energy applications.

In-situ introduction of CePO4 for stabilizing electrocatalytic activity of quasi-MOF with partially missing C≡N skeleton

Hydrogen (H2) is considered one of the most promising green energy sources due to its high combustion heat value and non-polluting byproducts after combusting. Electrolysis of water to product H2 is a safe and stable way. Nevertheless, the current commercially available electrocatalysts suffer from high cost and slow reaction kinetics, hindering the widespread application of electrocatalytic water splitting. Metal-organic framework (MOF) have been concerned widespread as materials with high activity sites in the field of electrocatalyst. However, the presence of organic frameworks in MOF results in slow electron transfer rates and weak catalytic activity. To address this issue, this research has constructed a novel CePO4/quasi-MOF heterostructure with partial amorphous phase. The partial absence of organic frameworks in this heterostructure exposes more active metal sites, while the presence of the amorphous phase enhances the porosity of material. The overpotentials (η10) of CePO4/Ce-PBA-2 for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are 242 and 192 mV, respectively. The density functional theory (DFT) calculations demonstrate that constructing the CePO4/Ce-PBA-2 heterostructure with missing C≡N frameworks partially accelerates the electron transfer between metal ions, improving the reaction kinetics of HER and OER effectively. On the other hand, CePO4/Ce-PBA-2 exhibited a specific capacitance of 1346.7F g−1 at 1 A/g. The CePO4/quasi-MOF heterostructure achieves efficient electrocatalytic water splitting and energy storage in supercapacitors simultaneously. This study further paves the way for the application and development of MOF in the field of electrochemistry.

One-step electrodeposition synthesis of bimetallic sulfides for highly efficient electrocatalytic water splitting

Investigation of highly effective and affordable metal-based electrocatalysts is crucial for water splitting that yields pure hydrogen. Herein, using one-step room-temperature electrodeposition, we successfully created a binary metal nickel-iron sulfide bifunctional electrocatalyst having plenty of active sites and a significant specific surface area on nickel foam (NF). Additionally, the synergistic interaction of the two metal components, iron and nickel, facilitates the electron transfer process and increases the materials’ electrocatalytic performance. To obtain 10 mA cm−2, the catalyst only requires 75 mV for HER and 210 mV for OER in 1.0 M KOH. The two-electrode electrolyzer only needs a modest driving voltage (1.46 V@10 mA cm−2). The research presented here offers fresh understandings into the water splitting of nickel-iron-based sulfides as well as a reasonable direction for the development of bifunctional electrocatalysts.