Catalysts For Electrochemical Water Splitting Research Articles

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 LaNi0.58 Fe0.38 P0.07 O3-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.

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.

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.

Ultra-fast electrochemical preparation of Ni-Cu-Fe nano-micro dendrite as a highly active and stable electrocatalyst for overall water splitting

The development of highly active, durable, and low-cost electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) to advance the commercial applications of overall water electrolysis is regarded as a crucial matter. We describe an ultra-fast synthesis of multi-metal Ni-Cu-Fe micro-nano dendritic electrocatalysts were synthesized on nickel foam using a simple one-step constant current electrodeposition method. According to DFT simulations, Fe incorporation causes a downshift movement in the d-band center and the formation of additional catalytic active sites. Ni-Cu-Fe nano-micro dendrites have potential applications as bifunctional catalysts for electrochemical water splitting. Also, the increased electrical conductivity of the Ni-Cu-Fe electrode is due to the placement of more electronic states near the Fermi level and creating an optimal and porous dendritic structure that causes better electrolyte penetration in the pores. Experiments show that in the 1.0 M KOH electrolyte, Ni-Cu-Fe catalysts need an ultra-low overpotentials of 42 mV and 300 mV to supply a current density of −10 mA cm−2 for the HER and 50 mA cm−2 for the OER. Also, when Ni-Cu-Fe electrocatalyst is used as a bifunctional electrode in the overall water splitting system, it displays a low cell voltage of 1.54 V in a current density of 10 mA cm−2 can maintain this activity for more than 100 h.

Intriguing 3D micro-flower structure of Co1.11Te2 deposited on Te nanosheets showing an efficient bifunctional electrocatalytic property for overall water splitting

The development of efficient and low-cost bifunctional catalysts for electrochemical water splitting is important for future sustainable hydrogen energy deployment. In this paper, a series of composition-controlled hybrid catalysts (Co1.11Te2/Te) were successfully constructed by introducing different proportions of Co source into the precursor solutions during the hydrothermal synthesis of Te nanosheets(Te NSs). The experimental results show that the content of Co3+active species in the hybrid materials can be adjusted by controlling the molar ratio of Co to Te, thereby significantly improving the electrocatalytic performance of the samples. Benefiting from the highest content of Co3+, the large specific surface area, and the great charge transfer ability, the Te-Co-3 electrode exhibited the best catalytic activity and durability among all samples. The hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) overpotentials of the electrode were only 135 and 261 mV, respectively, to drive a current density of 10 mA cm−2 in an alkaline environment (1 M KOH). Furthermore, it required only a cell potential of 1.56 V to achieve overall water splitting at 10 mA cm−2. This work should be useful for the design and preparation of non-noble metal bifunctional catalysts.

Biomimetic three-dimensional multilevel nanoarray electrodes with superaerophobicity as efficient bifunctional catalysts for electrochemical water splitting

Biomimetic three-dimensional multilevel nanoarray electrodes with superaerophobicity as efficient bifunctional catalysts for electrochemical water splitting

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.

Ball milling as an effective method for improving oxygen evolution reaction electrocatalyst Ca3Co4O9

Misfit-layered Ca3Co4O9 was investigated as oxygen evolution reaction catalyst for electrochemical water splitting. Oxygen vacancies can be effectively induced by ball milling as detected by electronic paramagnetic resonance and X-ray photoelectron spectrometer measurements. The electrochemical performance was investigated for the Ca3Co4O9 catalysts with different ball milling times. The results show that the sample with the ball milling time of 24 h possesses the best performance due to the induced oxygen vacancies as well as the enhanced specific surface area. This work will provide an effective route to improve the electrochemical oxygen evolution reaction performance of the misfit-layered cobaltates.

Template-assisted synthesis of ultrathin graphene aerogels as bifunctional oxygen electrocatalysts for water splitting and alkaline/neutral zinc-air batteries

Low-cost, high-performance oxygen catalysts are critical for electrochemical water splitting and metal-air batteries. Herein, carbon aerogels with skeletons consisting of few-layer graphene are derived pyrolytically from a hydrogel precursor using an array of NaCl crystals as the template, exhibiting a high electrical conductivity (869 S m−1) and an ultralow mass density (11.1 mg cm−3). The deposition of NiFe layered double hydroxide (NiFe-LDH) nanocolloids renders the aerogels active towards both the oxygen reduction/evolution reactions (ORR/OER), with the performances highly comparable to those of commercial benchmarks in both alkaline and neutral media. Results from operando Raman spectroscopy measurements and first principles caculations suggest that Fe(OH)3 colloids facilitate the oxidation of Ni2+, which lowers the energy barrier to 0.42 eV for OER, whereas the nitrogen-doped carbon aerogels are responsible for the ORR activity. With the composites used as bifunctional oxygen catalysts for electrochemical water splitting and rechargeable zinc-air batteries, the performances in both alkaline and neutral media are markedly better than those based on the mixture of commercial Pt/C and RuO2. Results from this study highlight the unique advantages of ultrathin graphene aerogels in the development of effective catalysts for electrochemical energy devices.

Nano-scale new Heusler compounds NiRh2Sb and CuRh2Sb: synthesis, characterization, and application as electrocatalysts

New Heusler compounds NiRh2Sb and CuRh2Sb are synthesized in nano-scale and in bulk. The nanoparticles prove to be excellent catalysts for electrochemical water splitting.