Catalysts For Overall Water Splitting Research Articles

Co2Mo3O8/Nb2O5 heterojunctions with rich oxygen vacancies wrapped in cobalt embedded carbon hollow cubic nanoboxes greatly improves the oxygen evolution performance and stability for water splitting

Herein, Co2Mo3O8/Nb2O5 heterojunctions with rich oxygen vacancies wrapped in cobalt embedded carbon hollow cubic nanoboxes (Co(Mo,Nb)@MCNBs) derived from metal-organic frameworks (MOFs) is synthesized by hydrothermal reaction, bimetallic cation doping, high-temperature carbonization. The synergistic effect and strong electron coupling interaction between Co2Mo3O8/Nb2O5 heterojunctions and cobalt embedded carbon hollow cubic nanoboxes result in a more uniform distribution of heterojunctions on the surface of Co@MCNBs, more catalytic active sites are exposed and the catalytic performance is improved. It only requires an overpotential of 284 mV to drive the current density of 10 mA cm−2 towards oxygen evolution reaction (OER), which is significantly lower than most previously reported catalysts and commercial RuO2. Furthermore, the Co(Mo,Nb)@MCNBs exhibits exceedingly good long-term stability with the current density retention rate of 98.1% after 43,200 s for OER, which even still outperform the commercial RuO2 catalyst. More interestingly, the electrolyzer Co(Mo,Nb)@MCNBs(+)||Co@MCNBs(-) demonstrates an excellent cycling stability and outperforms RuO2(+)||Pt/C(-), suggesting the actual availability of Co(Mo,Nb)@MCNBs in overall water splitting. The synergic effect of heterostructures design of the Co(Mo,Nb)@MCNBs catalyst for overall water splitting will promote the mass production of hydrogen with high-efficiency and low-cost.

Electronic-State Modulation of Metallic Co-Assisted Co7 Fe3 Alloy Heterostructure for Highly Efficient and Stable Overall Water Splitting.

Manipulating electronic structure of alloy-based electrocatalysts can eagerly regulate its catalytic efficiency and corrosion resistance for water splitting and fundamentally understand the catalytic mechanisms for oxygen/hydrogen evolution reactions (OER/HER). Herein, the metallic Co-assisted Co7 Fe3 alloy heterojunction (Co7 Fe3 /Co) embeds in a 3D honeycomb-like graphitic carbon is purposely constructed as a bifunctional catalyst for overall water splitting. As-marked Co7 Fe3 /Co-600 displays the excellent catalytic activities in alkaline media with low overpotentials of 200mV for OER and 68mV for HER at 10mAcm-2 . Theoretical calculations reveal the electronic redistribution after coupling Co with Co7 Fe3 , which likely forms the electron-rich state over interfaces and the electron-delocalized state at Co7 Fe3 alloy. This process changes the d-band center position of Co7 Fe3 /Co and optimizes the affinity of catalyst surface to intermediates, thus promoting the intrinsic OER/HER activities. For overall water splitting, the electrolyzer only requires a cell voltage of 1.50V to achieve 10mAcm-2 and dramatically retains 99.1% of original activity after 100h of continuous operation. This work proposes an insight into modulation of electronic state in alloy/metal heterojunctions and explores a new path to construct more competitive electrocatalysts for overall water splitting.

Assembly Engineering of Rh Atoms on CoAl-Layered Double Hydroxide Nanosheets for Boosting Alkaline Water Splitting

Layered double hydroxides (LDHs), especially Co-based LDHs, are regarded as a class of promising electrocatalysts toward overall water splitting, due to their good performance in oxygen evolution reaction (OER). However, inferior activity toward hydrogen evolution reaction (HER) hinders their scale-up applications. Here, a one-step hydrothermal strategy is proposed to fabricate 3D self-supported Rh-incorporated CoAl LDH (Rh/CoAl LDH) nanosheet arrays as bifunctional catalysts for overall water splitting. The thickness and lateral size of CoAl LDHs depend strongly on the introduced content of Rh atoms. Importantly, Rh incorporation distorts the local atomic arrangement owing to different atom sizes on the CoAl laminate. The strong interaction between Rh atoms and CoAl LDHs dramatically boosts the HER activity by facilitating HER kinetics and improves the OER performance simultaneously. The Rh/CoAl-300 LDH electrode with optimized composition only requires an overpotential of 71 mV to reach 10 mA/cm2 for HER and 390 mV to achieve 100 mA/cm2 for OER. The alkaline electrolyzer assembled by bifunctional Rh/CoAl-300 LDH electrodes only needs a cell voltage of 1.54 V at an overall water splitting of 10 mA/cm2.

Electrodeposition of copper-cobalt bimetallic phosphide on nickel foam as an efficient catalyst for overall water splitting

The application of non-precious metal bifunctional electrode materials is relevant to solving the current serious energy and environmental problems. In this study, the Cu-Co-P/NF bifunctional electrocatalyst with grape-like clusters was successfully prepared for water splitting using nickel foam (NF) as a substrate by electrodeposition. In alkaline conditions, the catalysts showed good catalytic activity and stability in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). At 10 mA cm-2, the overpotential required for HER was only 64 mV, whereas for OER it was 334 mV, with Tafel slopes of 40 mV dec-1 and 74 mVdec-1, respectively, and almost negligible potential fluctuations after 49 h and 52 h of testing under continuous electrolysis. Furthermore, the two-electrode electrolyzer required only 1.55 V to achieve 10 mA cm-2 in 1 M KOH solution when Cu-Co-P/NF was used as both cathode and anode for water splitting, which was superior to most previously reported electrocatalysts, and it also showed good durability in a 82 h test. Therefore, it has promising applications in industrial electrolytic systems. The unusual Cu-Co-P/NF with grape-like clusters, as well as the synergistic effect between Co and Cu atoms and the high electrochemically active surface area (ECSA), are responsible for the remarkable catalytic performance.

Mo/P doped NiFeSe as bifunctional electrocatalysts for overall water splitting

Designing high-efficiency catalysts for overall water splitting is critical to reduce the cost of hydrogen fuel as a clean and renewable energy source in future society. In this work, a Mo-, P-codoped NiFeSe was successfully synthesized on nickel foam (NF) by one-step electrodeposition. Through the doping strategy, the conductivity can be well promoted, and the production of nanosheets on the catalyst surface and active phases during hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) provided much more active sites, which leaded to efficient HER/OER performances of as-synthesized Mo-, P-codoped NiFeSe catalysts, i.e., a low overpotential of 100 mV/200 mV at current density of 10 mA cm−2 in 1.0 M KOH with stability of 95 h/60 h, respectively. It only required 1.53 V to deliver a current density of 10 mA cm−2 in overall water splitting and maintained outstanding durability for 100 h. This work is beneficial to future design of high efficient and low-cost bifunctional catalysts for overall water splitting.

Constructing robust NiFe LDHs–NiFe alloy gradient hybrid bifunctional catalyst for overall water splitting: one-step electrodeposition and surface reconstruction

Constructing robust NiFe LDHs–NiFe alloy gradient hybrid bifunctional catalyst for overall water splitting: one-step electrodeposition and surface reconstruction

In-situ construction of hexagonal-star-shaped MnCo2S4@MoS2 boosting overall water splitting performance at large-current-density: Compositional-electronic regulation, functions, and mechanisms

It remains to be challenging to develop bifunctional catalysts for overall water splitting (OWS) with high activity and durability at large current density. In an attempt to overcome this bottleneck, unique MnCo2S4 hexagonal stars covered with MoS2 nanosheets were in-situ grown on nickel foam (NF) to obtain MnCo2S4@MoS2/NF heterostructure with optimized composition and local electronic structure in this work. When employed as a bifunctional catalyst, it only needs low overpotentials of 208 and 332 mV in 6.0 M KOH to drive 1000 mA cm−2 with small Tafel slopes of 56.8 and 75.6 mV dec-1 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. In addition, MnCo2S4@MoS2/NF showed remarkable stability in simulated industrial conditions, operating stably for 50 h at 1000 mA cm−2 without any attenuation for HER/OER. Thus, the MnCo2S4@MoS2/NF can function as a bifunctional electrocatalyst for OWS, only requiring 1.795 V to afford 1000 mA cm−2 with splendid stability. The improved performance is ascribed to dual electric and compositional regulation, which endow MnCo2S4@MoS2/NF with rich active sites and heterointerfaces, thereby promoting electron transfer and boosting the reaction kinetic. Furthermore, density functional theory (DFT) calculations reveal that the construction of heterostructure can help regulate intrinsic electronic structure, resulting in accelerated reaction kinetics. This work provides a reasonable and meaningful method for boosting industrial green hydrogen production.

2D porous Co-Mo nitride heterostructures nanosheets for highly effective electrochemical water splitting

A significant issue in the overall water splitting process is the development of bifunctional non-precious metal catalysts with high performance. Herein, we designed and synthesized heterogeneous structure of Co5.47N/MoN (Co-Mo-N) porous nanosheets in situ grown on nickel foam substrates by thermal ammonolysis of CoMoO4 precursors. The special heterogeneous and porous nanosheet structure of Co-Mo-N not only provides abundance of active sites, but also accelerates the charge transfer due to the interaction between Co5.47N and MoN. Additionally, the differing energy band configurations of the various phases in heterostructure will cause charge transport at the interface, which would be advantageous for the surface electron modification of heterojunctions and further enhances the electrocatalytic performance. As a result, the Co-Mo-N heterostructure exhibited excellent OER and HER catalytic activity, with over potentials of 288 and 82 mV at 10 mA cm−2, respectively. When using Co-Mo-N heterostructures as cathodes and anodes to achieve overall water splitting, a low voltage of 1.59 V is required to achieve a current density of 10 mA cm−2. This research presents a novel approach to designing bifunctional non-precious metal catalysts for overall water splitting.

A hierarchical cactus-like nanostructure as a bifunctional catalyst for overall water splitting

In this study, a hierarchical cactus-like nanostructure with cobalt doped iron disulfide (Co-FeS2) needle nanowires as trunks and nickel-iron layered double hydroxide (NiFe-LDH) nanosheets as branches was constructed as a self-supporting electrode for overall water splitting in alkaline electrolytes. A low electron density NiFe-LDH derived from the strong electronic interaction between sulfides and NiFe-LDH is remarkably effective in facilitating the adsorption of H2O and OH−, while the presence of Co atoms in FeS2 facilitates the hydrogen adsorption. Such a synergetic effect improved the HER performance in alkaline electrolytes significantly. In terms of the OER process, the Fe/Co oxyhydroxides produced from in situ phase transition from Co-FeS2 in conjunction with NiFe-LDH endow the electrode with excellent OER activity. Furthermore, the Co-FeS2 needle nanowires with metal-like conductivity allow for rapid electron transfer during electrochemical processes, and the hierarchical structure exposes substantial active sites and facilitates electrolyte penetration. In alkaline media, the electrode demonstrated outstanding HER and OER catalytic activity, requiring small overpotentials of 131 mV and 220 mV to reach current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, it only needed 1.58 V to drive 10 mA cm−2 when utilized simultaneously as both cathode and anode for overall water splitting.

Pt modified NiMoO4-GO/NF nanorods with strong metal-support interaction as efficient bifunctional catalysts for overall water splitting

Catalysts for the electrolysis of water are critical in the production of hydrogen for the energy industry. The use of strong metal-support interactions (SMSI) to modulate the dispersion, electron distribution, and geometry of active metals is an effective strategy for improving catalytic performance. However, in currently used catalysts, the supporting effect does not significantly contribute directly to catalytic activity. Consequently, the continued investigation of SMSI, using active metals to stimulate the supporting effect for catalytic activity, remains very challenging. Herein, the atomic layer deposition technique was employed to prepare an efficient catalyst composed of platinum nanoparticles (Pt NPs) deposited on nickel-molybdate (NiMoO4) nanorods. Nickel-molybdate’s oxygen vacancies (Vo) not only help anchor highly-dispersed Pt NPs with low loading but also strengthen the SMSI. The valuable electronic structure modulation between Pt NPs and Vo resulted in a low overpotential of the hydrogen and oxygen evolution reactions, returning results of 190 mV and 296 mV, respectively, at a current density of 100 mA cm−2 in 1 M KOH. Ultimately, an ultralow potential (1.515 V) for the overall decomposition of water was achieved at 10 mA cm−2, outperforming state-of-art catalysts based on the Pt/C || IrO2 couple (1.668 V). This work aims to provide reference and a concept for the design of bifunctional catalysts that apply the SMSI effect to achieve a simultaneous catalytic effect from the metal and its support.

Strain engineering of high-entropy alloy catalysts for electrocatalytic water splitting

Developing active and cost-effective bifunctional electrocatalysts for overall water splitting is challenging but mandatory for renewable energy technologies. We report a high-entropy alloy (HEA) of PtIrCuNiCr as a bifunctional electrocatalyst for overall water splitting, which shows a low overpotential of ca. 190mV at the current density of 10mAcm-2. Compared with pure metals, HEAs exhibit remarkable surface strain due to severe lattice distortion in their crystal structures. Theoretical calculations reveal that the strain can regulate the binding energy of intermediates on catalysts by adjusting the metal-metal bonding energy. It pushes the HEA toward the top of volcano plots to achieve superior electrocatalytic activity for both hydrogen and oxygen evolution reactions. The strain effect of HEAs on electrocatalysis can be well engineered by tuning the catalyst radius or configurational entropy. This work renders a systematic strain regulation strategy for designing a high-performance HEA catalyst for overall water splitting.

Alternating magnetic field improved NiFe@MoS2 monolayer diatomic site catalyst for overall water splitting

Further uprating the catalytic activities of diatomic active sites while maintaining the atomic loading and diatomic coordination by external stimulation is a promising way to break the bottleneck in the improvement of diatomic site catalysts (DASCs). Herein, the as-prepared NiFe@MoS2 DASCs treated by external high-frequency alternating magnetic field (AMF) further expedite the alkaline water electrolysis process with a superior cell voltage of 1.576 V to afford a current density of 10 mA cm−2 than that treated without AMF (1.652 V). Theoretical simulation by COMSOL Multiphysics helps visualize the increase in temperature locally around the diatomic active sites, qualitatively revealing the magnetic heating effect that originates from the anchored magnetic Ni and Fe atoms. The selective magnetic heating of bifunctional diatomic active site proposed in this work can broaden horizons and endow another dimension in the design of highly efficient catalysts toward various complicated energy-related reactions.

Manganese cobalt sulfide/molybdenum disulfide nanowire heterojunction as an excellent bifunctional catalyst for electrochemical water splitting

Heterointerface engineering enhances catalytic active centers and charge transfer capabilities to increase oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) kinetics. In this study, a novel heterostructure of manganese cobalt sulfide-molybdenum disulfide on nickel foam (MnCo2S4-MoS2/NF) was synthesized via a two-step hydrothermal process. The nanowire-shaped MnCo2S4-MoS2 on NF displayed accelerated charge transfer ability and multiple integrated active sites. When tested in one molar (1 M) potassium hydroxide (KOH) electrolyte, it furnished low overpotentials of 105 and 171 mV for the HER and 220 and 300 mV for the OER at the current densities of 20 and 50 mA cm−2, respectively. An electrolyzer based on MnCo2S4-MoS2/NF required low operating potentials of 1.41 and 1.49 V to yield the current densities of 10 and 20 mA cm−2, respectively, surpassing commercial and previously reported catalysts. Density functional theory (DFT) analysis revealed that the MnCo2S4-MoS2 heterostructure possesses the optimal adsorption free energies for the reactants, an extended electroactive surface area, good charge transfer ability, and reasonable density of electronic states close to the Fermi level, all of which contribute to the high activity of catalyst. Thus, heterointerface engineering is a promising strategy for creating efficient catalysts for overall water splitting.

Constructing microstructures in nickel-iron layered double hydroxide electrocatalysts by cobalt doping for efficient overall water splitting

The development of Ni–Fe layered double hydroxide (NiFe LDH) catalysts for overall water splitting (OWS) is urgently required. NiFe LDHs are promising catalysts for the oxygen evolution reaction (OER). However, their hydrogen evolution reaction (HER) performance is restricted by slow kinetics. The construction of multiple types of active sites to simultaneously optimise the OER and HER performance is significant for OWS using NiFe LDHs. Hence, a Co-doped NiFe LDH electrocatalyst with dislocations and stacking faults was designed to modulate the electronic structure and generate multiple types of activity sites. The Co0.03-NiFe0.97 LDH catalyst only required overpotentials of 280 (50 mA cm−2, OER) and 170 mV (10 mA cm−2, HER). However, it reached a current density of 50 mA cm−2 at 1.53 V during OWS. Co0.03-NiFe0.97 LDHs could be stabilised for 140 h at 1.52 V. Furthermore, Co0.03-NiFe0.97 LDHs exhibited a higher electrocatalytic activity than commercial Raney nickel and Pt/C||IrO2 under industrial conditions. The significant specific surface area, high conductivity, and unique microstructures are the major factors contributing to the excellent OWS performance. This study suggests an efficient strategy for introducing microstructures to fabricate catalysts with high activity for application in OWS.

One-Step Hydrothermal Synthesis of Cobalt Sulfide/E-Waste Derived Activated Carbon Nanocomposite as a Bifunctional Electrocatalyst for Overall Water-Splitting

An electrocatalyst with high performance can enhance the hydrogen production for overall water-splitting. This study reports on the e-waste-derived activated carbon encapsulated cobalt sulfide (CoS2/AC) nanocomposite synthesized via a simple hydrothermal process for overall water-splitting application. The microstructural image of CoS2/AC showed the aggregated stacked nanosheets of activated carbon encapsulating the cobalt sulfide nanoparticles. The nanocomposite of CoS2/AC exhibited the overpotential of 240 mV at 10 mA cm−2 and a 34 mV dec−1 of Tafel slope value with extraordinary stability for OER. On the other hand, the nanocomposite exhibited the overpotential of 378 mV at 10 mA cm−2 with a Tafel slope of ∼134 mV dec−1 with splendid stability in 1 M KOH solution for HER. The enhanced electrical conductivity and electrochemically active surface area of the AC nanosheets and CoS2 nanoparticles in this nanocomposite account for its higher electrocatalytic activity. Thus, the hydrothermally synthesized CoS2/AC presents itself as a better bifunctional catalyst for overall water-splitting.

Theoretical screening of synergistic transition metal dual-atom catalysts for overall water splitting

Double-atom catalysts (DACs) with bimetallic active sites can produce a synergistic effect between the neighbouring metallic sites, which can further enhance the catalytic activity. In this work, DFT calculations are used to screen lots of DACs as effective bifunctional electrocatalysts for overall water splitting. Through the comparative study between the DACs and single-atom catalysts (SACs), we found that DACs show higher overall water splitting activity than corresponding SACs counterparts, attributing to the synergistic effect between the adjacent active sites which play a vital role in fine tuning the binding strength of the reaction intermediates. The d-band center and charge transfer as descriptors are used to explain the activity origin of DACs. This work highlights that DACs with bimetallic active sites are promising for designing bifunctional catalysts for overall water splitting.

Engineering edge sites based on NiS2/MoS2/CNTs heterojunction catalyst for overall water splitting

Boosting the hydrogen and oxygen evolution reaction (HER/OER) on MoS2-based catalysts is a challenging scientific issue due to the activity of MoS2 is significantly rely on the edge site which is limited in regular structure. Herein, a highly dispersed edge site-rich NiS2/MoS2/CNTs heterojunction catalyst is successfully developed via facile etching the nanoflower-like NiS2/MoS2 spheres on carbon nanotubes (CNTs). Through expanding the lattice spacing of 2H-MoS2, generating abundant Mo-S edge sites (i.e. generating a large number of unsaturated S atoms) together with enhancing the dispersity of NiS2/MoS2 nanosheets, the etching posttreatment significantly regulates the electronic and geometric structure of NiS2/MoS2/CNTs. Further combining the extremely intimate electronic interaction between MoS2/NiS2 heterogeneous interfaces, the optimal NiS2/MoS2/CNTs presents a preeminent alkali water splitting performance with overpotentials of 149 for HER and 315 mV for OER at 10 mA cm−2, which are 29 and 35 mV lower than the catalyst before etch treatment (NiS2/MoS2/CNTs-p), respectively. Moreover, the electrolyzer assembled with NiS2/MoS2/CNTs drives a voltage of 1.73 V at 10 mA cm−2 and a continuous stable operation of 50 h toward overall water splitting.

Accelerating corrosion of iron foam enables a bifunctional catalyst for overall water splitting

A bifunctional NiFe nanoparticle-modified layered double hydroxide nanosheet electrocatalyst was fabricated using a facile NH4Cl-assisted corrosion strategy at room temperature for highly efficient overall water splitting.

Substrate self-derived porous rod-like NiS/Ni9S8/NF heterostructures as efficient bifunctional electrocatalysts for overall water splitting.

A self-derivation strategy using conductive substrates is used to prepare one-piece highly efficient bifunctional electrodes, where the chosen substrate acts as both an active catalyst precursor and a conductive carrier. Here, a bifunctional catalyst, porous NiS/Ni9S8/NF-2 nanorods, was synthesized by low-temperature vulcanization after an oxalic acid etching process. To reach a current density of 10 mA cm-2, NiS/Ni9S8/NF-2 requires only a tiny overpotential of 115 mV for the HER and 176 mV for the OER, and demonstrates sustained activity for 100 hours with almost any degradation. The substrate self-derived NiS/Ni9S8/NF-2 catalyst for overall water splitting requires only a small voltage of 1.52 V to deliver 10 mA cm-2 with excellent stability. Experimental results show that the heterostructured electrocatalysts impart good catalytic properties of NiS/Ni9S8/NF-2 by modulating the electronic structure and promoting the reconstruction process from sulfides to hydroxides. This work demonstrates the success of the substrate self-derivation strategy to achieve high catalytic activity and provide a new autogenous growth technique for electrode fabrication.

Electronic modulation of heterostructured MoOx supported Ru as robust bifunctional catalyst for overall water splitting

Ru–MoOx heterostructure exhibits excellent electrocatalytic performance for overall water splitting.