Catalysts For Electrochemical Water Splitting Research Articles

Recent Development of Transition Metal‐based Amorphous Electrocatalysts for Water Splitting

AbstractElectrochemical water splitting, including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is a promising hydrogen production technology. However, in practice, the high overpotentials and sluggish reaction kinetics associated with the anode OER process are the major obstacles to the smooth progress of electrocatalytic water splitting. Amorphous electrocatalysts, a crucial family of functional materials, exhibit unexpected performance due to their special short‐range ordered and long‐range disordered atom arrangement, abundant defect sites and adjustable composition. To date, while numerous recent publications showcase promising results for transition metal‐based amorphous electrocatalysts, including amorphous metal phosphide and metal hydroxide electrocatalysts with remarkable HER and OER properties respectively, the utilization of single‐function HER or OER catalysts tends to augment system complexity for water electrolysis, thereby escalating the cost of hydrogen production. In this regard, amorphous HER/OER bifunctional electrocatalysts are desired. In this review, we summarize the recent development on transition metal‐based amorphous catalysts for electrochemical water splitting. The design strategies for constructing HER/OER bifunctional transition‐metal‐based amorphous electrocatalysts are highlighted here, also including the exploration of relationship between catalyst structures and their remarkably improved performance. Finally, the possibilities of amorphous bifunctional catalysts for practical industrial applications are evaluated and future research direction are suggested.

Enhanced oxygen evolution reaction using carbon-encapsulated Co-Fe-Al Alloy

Transition metal-based alloy nanostructures have emerged as promising catalysts for electrochemical water splitting, offering a potential solution to the growing demand for clean and renewable energy. Also, research on encapsulation engineering of alloy nanostructures using carbon matrices has recently advanced, presenting a new approach that combines the conductive properties of carbon matrices with an alloy structure to enhance electrochemical performance in water splitting. However, the specific roles of the alloy core, carbon shell, and their synergistic effect in improving electrochemical performance are still not well understood. In this paper, we report on the encapsulation of a ternary Co–Fe–Al alloy nanostructure using a carbon matrix and investigate its electrochemical oxygen evolution reaction (OER). The optimized carbon matrix-encapsulated Co0.3Fe0.2Al0.5 alloy catalyst demonstrated superior electrocatalytic activity for OER (achieving 250 mV at 10 mA cm−2) and long-term stability. Through density functional theory calculations, we also elucidate the crucial role of Al in enhancing the OER catalytic performance of the proposed carbon-encapsulated Co–Fe alloy catalyst. By comparing the free electron concentration and required applied potentials to trigger OER, we provide insights into the beneficial effects of incorporating Al into the Co–Fe alloy catalyst.

Rapid Synthesis of Ruthenium-Copper Nanocomposites as High-Performance Bifunctional Electrocatalysts for Electrochemical Water Splitting.

Development of high-performance, low-cost catalysts for electrochemical water splitting is key to sustainable hydrogen production. Herein, ultrafast synthesis of carbon-supported ruthenium-copper (RuCu/C) nanocomposites is reported by magnetic induction heating, where the rapid Joule's heating of RuCl3 and CuCl2 at 200A for 10s produces Ru-Cl residues-decorated Ru nanocrystals dispersed on a CuClx scaffold, featuring effective Ru to Cu charge transfer. Among the series, the RuCu/C-3 sample exhibits the best activity in 1m KOH toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with an overpotential of only -23 and +270mV to reach 10mAcm-2, respectively. When RuCu/C-3 is used as bifunctional catalysts for electrochemical water splitting, a low cell voltage of 1.53V is needed to produce 10mAcm-2, markedly better than that with a mixture of commercial Pt/C+RuO2 (1.59V). In situ X-ray absorption spectroscopy measurements show that the bifunctional activity is due to reduction of the Ru-Cl residues at low electrode potentials that enriches metallic Ru and oxidation at high electrode potentials that facilitates the formation of amorphous RuOx. These findings highlight the unique potential of MIH in the ultrafast synthesis of high-performance catalysts for electrochemical water splitting.

Microwave synthesis of Ni5P4 nanosheets for efficient overall water splitting

Electrocatalytic water splitting is crucial for H2 production, which faces challenges with expensive and scarce noble metal catalysts. There is a persistent need for affordable, efficient electrodes facilitating both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). This study introduces a facile microwave synthesis method for nickel phosphide nanosheets (Ni5P4 NSs). These NSs demonstrate low overpotentials 110 mV for HER, 235 mV for OER at 10 mA cm−2 in 1 M KOH. Additionally, they show excellent overpotential 1.44 V at 10 mA cm−2 and remarkable durability for overall water splitting in the same conditions. This research highlights Ni5P4 NSs as promising bifunctional catalysts for electrochemical water splitting, offering a cost-effective and efficient alternative to noble metal catalysts in energy storage and conversion applications.

Surface reconstruction of ruddlesden–popper-based oxides in nonreactive environments and under electrochemical conditions for the oxygen evolution reaction

Perovskite oxides have emerged as catalysts for electrochemical water splitting, and surface reconstruction is crucial for their electrocatalytic performance. In this study, we report the surface reconstruction of Ruddlesden–Popper-based oxides under nonreactive and electrochemical conditions. The rapid migration of Sr ions from the bulk to the surface results in a porous structure, increase the number of oxygen vacancies, and produces an A-site cation deficiency. Collectively, these modifications significantly enhance the electrocatalytic activity and stability for water oxidation. In addition, the engineered electrocatalysts have a low overpotential of 350 mV at 10 mA cm−2, alone with a Tafel slope of 77 mV dec−1. They also exhibit outstanding durability, maintaining a current density of 5 mA cm−2 over 6 h.

Palladium–ruthenium binary alloy nanosheets as catalyst for electrochemical water splitting

Palladium–ruthenium binary alloy nanosheets as catalyst for electrochemical water splitting

Deep eutectic solvent-induced controllable synthesis of bifunctional Ni–Fe–P catalysts for electrochemical water splitting

Developing electrocatalysts with excellent activity, high stability, and low cost is vital for large-scale hydrogen production through electrochemical water splitting. Herein, a bifunctional Ni–Fe–P catalyst in situ grown on Fe foam (Ni–Fe–P/FF) is developed by a simple one-step solvothermal process in the deep eutectic solvent (DES) of ethylene glycol and choline chloride (named Ethaline). The unique solvent environment of Ethaline assisted with the regulating effect of the introduced Fe(III) ions shows an essential role in governing the preparation process. The developed Ni–Fe–P/FF acts as the efficient bifunctional electrocatalyst for water splitting in 1.0 M KOH, requiring overpotentials of 82 mV (229 mV) and 263 mV (370 mV) to deliver 10 mA cm−2 (100 mA cm−2) for oxygen and hydrogen evolution reactions, respectively. Furthermore, the self-supported catalyst-assembled electrolyzer also exhibits good catalytic performance with a low voltage of 1.83 V to drive 100 mA cm−2 and good stability over 100 h. This work offers a facile approach to fabricating high-performance bifunctional Ni–Fe–P electrocatalysts to catalyze water splitting.

P-Incorporation Induced Enhancement of Lattice Oxygen Participation in Double Perovskite Oxides to Boost Water Oxidation.

Activating the lattice oxygen in the catalysts to participate in the oxygen evolution reaction (OER), which can break the scaling relation-induced overpotential limitation (> 0.37V) of the adsorbate evolution mechanism, has emerged as a new and highly effective guide to accelerate the OER. However, how to increase the lattice oxygen participation of catalysts during OER remains a major challenge. Herein, P-incorporation induced enhancement of lattice oxygen participation in double perovskite LaNi0.58Fe0.38P0.07O3-σ (PLNFO) is studied. P-incorporation is found to be crucial for enhancing the OER activity. The current density reaches 1.35mA cmECSA -2 at 1.63V (vs RHE), achieving a sixfold increase in intrinsic activity. Experimental evidences confirm the dominant lattice oxygen participation mechanism (LOM) for OER pathway on PLNFO. Further electronic structures reveal that P-incorporation shifts the O p-band center by 0.7eV toward the Fermi level, making the states near the Fermi level more O p character, thus facilitating LOM and fast OER kinetics. This work offers a possible method to develop high-performance double perovskite OER catalysts for electrochemical water splitting.

Cobalt-free layered perovskites RBaCuFeO5+δ (R = 4f lanthanide) as electrocatalysts for the oxygen evolution reaction.

Co-based perovskite oxides are intensively studied as promising catalysts for electrochemical water splitting in an alkaline environment. However, the increasing Co demand by the battery industry is pushing the search for Co-free alternatives. Here we report a systematic study of the Co-free layered perovskite family RBaCuFeO5+δ (R = 4f lanthanide), where we uncover the existence of clear correlations between electrochemical properties and several physicochemical descriptors. Using a combination of advanced neutron and X-ray synchrotron techniques with ab initio DFT calculations we demonstrate and rationalize the positive impact of a large R ionic radius in their oxygen evolution reaction (OER) activity. We also reveal that, in these materials, Fe3+ is the transition metal cation the most prone to donate electrons. We also show that similar R3+/Ba2+ ionic radii favor the incorporation and mobility of oxygen in the layered perovskite structure and increase the number of available O diffusion paths, which have an additional, positive impact on both, the electric conductivity and the OER process. An unexpected result is the observation of a clear surface reconstruction exclusively in oxygen-rich samples (δ > 0), a fact that could be related to their superior OER activity. The encouraging intrinsic OER values obtained for the most active electrocatalyst (LaBaCuFeO5.49), together with the possibility of industrially producing this material in nanocrystalline form should inspire the design of other Co-free oxide catalysts with optimal properties for electrochemical water splitting.

High performance, binder-free electrodes with single atom catalysts on doped nanocarbons for electrochemical water splitting synthesized using one-step thermally controlled delamination of thin films

Developing high performance catalysts for electrochemical water splitting is critical for an efficient and sustainable route to hydrogen production.

Pressed Ni/MFe2O4 (M = Ni, Co) powder compacts for application as bifunctional, high-performance electrodes in electrochemical water splitting

The development of active, stable, earth-abundant, and cheap catalysts is crucial for renewable energy conversion devices. Catalysts for electrochemical water splitting are prepared using cold uniaxial pressing and consist of a superficial ferrite coating on a nickel substrate. The activity and mechanism of the oxygen (OER) and hydrogen (HER) evolution reactions on powder compacts are investigated. It is found that powder compacts are efficient catalysts for oxygen and hydrogen evolution in a 1 M KOH solution. For Ni/NiFe2O4, the current density of 10 mAcm−2 in OER and −10 mAcm−2 in HER shows overpotentials of 272 mV and −43 mV, respectively. In turn, for Ni/CoFe2O4, those overpotentials are 279 mV and −37 mV. Furthermore, using the same material for the anode and cathode in a two-electrode cell configuration, one can achieve a 10 mAcm−2 water splitting current at only 1.55 V for over 48 h without coating degradation. It is stated that the high activity towards OER and HER results from the large electrochemically active surface area and high electrical conductivity of powder compacts. The results also indicate that the most probable rate-determining steps for OER and HER are the formation of the adsorbed oxide atom and H2 molecule, respectively.

High entropy materials: potential catalysts for electrochemical water splitting

A comprehensive overview of the use of HEM as a catalyst for HER, OER, and water splitting was provided.

Dynamically assisted electrodeposition by hydrogen bubbles on carbonized wood: A NiFeCo nanoflower electrocatalyst for efficient hydrogen evolution

The development of cost-effective, simple, and highly active catalysts for electrochemical water splitting in alkaline electrolytes to produce renewable source H2 is critical to solve the environmental pollution and energy crisis. In this study, a series of nanoflower-like NiFeCo/CW catalytic electrodes were prepared by a facile one-step dynamic hydrogen bubble template (DHBT) method for electrodeposition on carbonized wood (CW), which have excellent HER performance. By reasonably investigating the effects of H+ concentration and time, a catalyst with ideal deposition results was obtained. In 1 M KOH solution, the prepared NiFeCo/CW-450 catalyst exhibits a small overpotential of 37 mV to achieve a current density of 10 mA cm−2, and still possess a satisfactory low overpotential when a larger current density is reached (η400 = 238 mV, η1000 = 298 mV). Furthermore, NiFeCo/CW can keep structure and catalytic performance stable after long-term test. The remarkable HER performance results from the unique nanoflower electrode structure that is uniformly dispersed on CW to fully expose the active site. As a result, this work will provide new inspiration and strategy for the preparation of novel simple, inexpensive and efficient electrocatalytic hydrogen evolution electrodes using earth-abundant resources.

Synergistic effects of nitrogen-doped carbon and praseodymium oxide in electrochemical water splitting

Hybrid materials featuring perovskite-type metal oxide in conjunction with heteroatom-doped graphene hold immense promise as alternatives to costly noble metal catalysts for electrochemical water splitting, facilitating the generation of environmentally friendly hydrogen. In this study, perovskite-type oxide containing praseodymium, barium, strontium, cobalt, and iron atoms dispersed in a carbon matrix as a catalyst is synthesized via annealing of the carbon material with substrates for the preparation of perovskite oxide. The mass ratio of reagents regulates the porous structure and elemental composition. The result of the hydrogen evolution reaction (HER), suggests that the hybrid catalysts exhibit intermediate HER kinetics compared to the commercial Pt/C and the catalyst without carbon. The Tafel slope for HER is lower for materials containing carbon, because of the improved reaction kinetics, facilitated proton transfer, and enhanced electrochemical surface area. Therefore, the study provides an effective strategy for the preparation of catalyst and their use as the active catalyst of water splitting.

Stainless steel as an electrocatalyst for overall water splitting under alkaline and neutral conditions

The development process for an effective catalyst for electrochemical water splitting must consider properties such as chemical and mechanical stability, corrosion resistance, and abundance alongside efficiency. In this work, a detailed electrochemical evaluation of four types of commercially available AISI stainless steel (302, 304, 316, and 321) was performed for their electrocatalytic activity, stability, and corrosion resistance in overall water splitting under alkaline (pH 14.00) and near-neutral conditions (pH 6.26). Using AISI plates directly as an anode or cathode, a current density of 10 mA cm−2 was obtained at η ≈ 0.38 V for OER and η ≈ 0.43 V for HER in 1 M KOH. Although all of the tested types have proved to be efficient electrocatalysts, detailed electrochemical studies have distinguished certain differences between the AISI types, depending mainly on the composition peculiarities. A detailed corrosion evaluation has revealed that although all measured stainless steels are sensitive to the oxidative environment, their corrosion rate does not exceed 3.3 µm per year.

Enhanced Metal-Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3N/NiO Heterojunction at Industrial CurrentDensity.

Developing highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure-induced-strategy to optimize the metal-support interaction (MSI) and the EWS activity of Ru-Ni3N/NiO. Density function theory (DFT) calculations firstly predicted that the Ni3N/NiO-heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru-Ni3N/NiO, compared to Ru-Ni3N and Ru-NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof-of-concept, the Ru-Ni3N/NiO catalyst with 2D Ni3N/NiO-heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which owns an excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm-2, respectively. Furthermore, the Ru-Ni3N/NiO-based EWS device can realize an industrial current density (1000 mA cm-2) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm-2) in alkaline pure water.

Enhanced Metal‐Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3N/NiO Heterojunction at Industrial Current Density

AbstractDeveloping highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure‐induced‐strategy to optimize the metal‐support interaction (MSI) and the EWS activity of Ru‐Ni3N/NiO. Density functional theory (DFT) calculations firstly predicted that the Ni3N/NiO‐heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru‐Ni3N/NiO compared to Ru‐Ni3N and Ru‐NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof‐of‐concept, the Ru‐Ni3N/NiO catalyst with a 2D Ni3N/NiO‐heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which exhibited excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm−2, respectively. Furthermore, the Ru‐Ni3N/NiO‐based EWS device can realize an industrial current density (1000 mA cm−2) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm−2) in alkaline pure water.

Metal-organic frameworks derived FeS2@CoS2 heterostructure for efficient and stable bifunctional electrocatalytic water splitting

The exploration of efficient metal-based bifunctional catalysts for electrochemical water splitting is a promising approach for large-scale applications. In this work, we constructed a FeS2@CoS2 heterostructure electrocatalyst by a facile solution-dipping and hydrothermal method. The optimum FeS2@CoS2 heterostructure showed notable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances, with overpotential values of 280 mV and 136 mV (10 mA cm−2 current density), respectively. Additionally, the electrocatalyst exhibited a robust stability performance of 50 h at a current density of 10 mA cm−2. The two-cell electrolyzer is assembled using FeS2@CoS2||FeS2@CoS2 and delivers a cell voltage of 1.62 V and 1.99 V at 10 and 50 mA cm−2 current densities with excellent durability. The outstanding overall water-splitting activity of the obtained heterostructure can be attributed to effective electronic interactions, synergistic effects, and exposure of more reactive active sites in the electrocatalyst. This work presents a promising strategy for developing highly active and cost-effective metal sulfide-based bifunctional electrocatalysts for energy conversion technology.

Ligand-Field Directed Electronic Effects in Heterogenized Bifunctional Co(II) Molecular Clusters Accomplish Efficient Overall Water Splitting

We demonstrate a hitherto unknown approach of employing cobalt organophosphate D4R cage-clusters, [(RO) PO3Co(L)]4 (1–4) and [nBu4N][F@{(RO)PO3Co(L)}4], (1F–4F), where L = DMSO (1 or 1F), pyridine (2 or 2F), 4-formylpyridine (3 or 3F), and 4-cyanopyridine (4 or 4F), as bifunctional heterogeneous catalysts for electrochemical water splitting in near-neutral conditions. Electronic and steric modifications on the clusters are achieved through a synergistic combination of endohedral trapping of fluoride ion and exohedral functionalization of pyridines. This two-pronged approach significantly reduces the charge density at the metal leading to energetically favorable water coordination with a perceptible enhancement in the kinetics of overall water splitting, with 4F exhibiting the lowest cell overpotential of 0.949 V (overall cell potential 2.179 V), observed among molecular catalysts. Density functional calculations highlight the importance of cooperativity between the cobalt centers. The unique D4R geometry stabilizes the high-valent metal-oxo/hydroperoxo species, emphasizing the need for polynuclear clusters to catalyze such challenging reactions, as has been well-established in the evolutionary PS-II.

Constructing Electrocatalysts with Composition Gradient Distribution by Solubility Product Theory: Amorphous/Crystalline CoNiFe‐LDH Hollow Nanocages

AbstractTransition‐metal based layered doubled hydroxides (LDH) as oxygen evolution reaction (OER) catalysts have attracted tremendous research interests. However, it is still a great challenge to strengthen the intrinsic activity of LDH. Herein, hollow CoNiFe‐LDH nanocages with amorphous/crystal phase and element gradient distribution are successfully constructed through the coordinated etching and precipitation process. Utilizing the difference of solubility product constants among transition metal cations to generate the gradient distribution effect in nanocages is proposed for the first time. The distinctive element gradient distribution in hollow CoNiFe‐LDH nanocages results in the composition gradient, which can provide the heterojunctions effect and play an important role in regulating morphology and electronic structure. Density functional theory calculations disclose that the synergistic effect between elements significantly regulates the electron density and enhances the conductivity. When employed as OER electrocatalysts, it exhibits a very competitive overpotential of 257 mV at 10 mA cm−2 combined with a low Tafel slope of 31.4 mV dec−1. This work represents a promising strategy to fabricate highly efficient OER catalysts for electrochemical water splitting and provides new opportunities to understand the promotion mechanism of intrinsic activity.