Electrocatalysts For Hydrogen Research Articles

Electrochemical Leaching of Ni Dopants in IrRu Alloy Electrocatalyst Boosts Overall Water Splitting

AbstractThe commercialization of water‐splitting technology strongly relies on the stable and high‐performance electrocatalyst for hydrogen and oxygen evolution reactions (HER‐OER). In this work, the nickel dopants in IrRu alloyed electrocatalyst for acidic water splitting activity are investigated. The incorporation of nickel dopants induces more oxygen atoms coordinating with Ir/Ru facilitating the formation of *OOH species via nucleophilic attack by H2O. Additionally, a fast surface reconstruction is achieved due to the electrochemical dissolution of Ni dopants; as a result, more oxygen species are incorporated, evidenced by in situ Raman spectroscopy and electrochemical impedance spectroscopy. Therefore, the mass activity for Ni@IrRu is enhanced by threefold than commercial IrO2 in acidic OER catalysis. Moreover, the nickel dopants balance the hydrogen binding strength; as a result, only 609 mV overpotential is demanded to reach 1 A cm−2 in acidic HER catalysis. The polymer electrolyte membrane water electrolyzer (PEMWE) test indicates only 1.87 V is required to attain 2 A cm−2, 160 mV lower than Pt/C‐IrO2 revealing its potential application in PEMWE.

Recent Advances in Vanadium-Based Electrocatalysts for Hydrogen and Oxygen Evolution Reactions: A Review

With the intensification of global resource shortages and the environmental crisis, hydrogen energy has garnered significant attention as a renewable and clean energy source. Water splitting is considered the most promising method of hydrogen production due to its non-polluting nature and high hydrogen concentration. However, the slow kinetics of the two key reactions, the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER), have greatly limited the development of related technologies. Meanwhile, the scarcity and high cost of precious metal catalysts represented by Pt and Ir/RuO2 limit their large-scale commercial application. Thus, it is essential to develop catalysts based on Earth’s transition metals that have abundant reserves. Vanadium (V) is an early transition metal with a distinct electronic structure from late transition metals such as Fe, Co, and Ni, which has been emphasized and studied by researchers. Numerous vanadium-based electrocatalysts have been developed for the HER and OER. In this review, the mechanisms of the HER and OER are described. Then, the compositions, properties, and modification strategies of various vanadium-based electrocatalysts are summarized, which include vanadium-based oxides, hydroxides, dichalcogenides, phosphides, nitrides, carbides, and vanadate. Finally, potential challenges and future perspectives are presented based on the current status of V-based electrocatalysts for water splitting.

In-situ synthesis of Ni2P/Ti3C2Tx hybrid nanosheets for enhanced alkaline hydrogen evolution reaction

The development of efficient and low-cost electrocatalysts for hydrogen in alkaline media is crucial for green energy production. Herein, we report an in-situ synthesis strategy of Ni2P/Ti3C2Tx hybrid nanosheets on nickel foam (NF), which is effectively achieved by direct phosphorization of Ni-MOF/Ti3C2Tx. The Ni2P/Ti3C2Tx hybrid nanosheets not only inherit the morphology of the Ni-MOF/Ti3C2Tx precursor, but also possess electronic coupling effects, thereby exhibiting enhanced electrocatalytic performance toward alkaline hydrogen evolution reaction (HER).

Stimulus of Work Function on Electron Transfer Process of Intermetallic Nickel-Antimonide Toward Bifunctional Electrocatalyst for Overall Water Splitting.

Engineering the intermetallic nanostructures as an effective bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is of great interest in green hydrogen production. However, a few non-noble metals act as bifunctional electrocatalysts, exhibiting terrific HER and OER processes reported to date. Herein the intermetallic nickel-antimonide (Ni─Sb) dendritic nanostructure via cost-effective electro-co-deposition method is designed and their bifunctional electrocatalytic property toward HER and OER is unrevealed. The designed Ni─Sb delivers a superior bifunctional activity in 1mKOH electrolyte, with a shallow overpotential of ≈119mV at -10mA for HER and ≈200mV at 50mA for OER. The mechanism behind the excellent bifunctional property of Ni─Sb is discussed via "interfacial descriptor" with the aid of Kelvin probe force microscopy (KPFM). This study reveals the rate of electrocatalytic reaction depends on the energy required for electron and proton transfer from the catalyst's surface. It is noteworthy that the assembled Ni─Sb-90 electrolyzer requires only a minuscule cell voltage of ≈1.46V for water splitting, which is far superior to the art of commercial catalysts.

Diamondoid Ni(II) Coordination Polymer as an Electrocatalyst for Hydrogen and Oxygen Evolution Reactions and Overall Water Splitting.

We have successfully synthesized a new Ni(II)-based coordination polymer (CP) [Ni2(cis-1,4-chdc)2(4,4'-bpy)3(H2O)2] (1); (cis-1,4- H2chdc=cis-1,4-cyclohexanedicarboxylic acid and 4,4'-bpy=4,4'-bipyridine) employing slow diffusion method in a single pot technique. The connectivity of Ni(II) ions and bridging cis-1,4-chdc ligand gives rise to a three-dimensional (3D) framework with 2-fold interpenetrated diamondoid topology. Interestingly, the synthesized CP acts as efficient catalyst for electrocatalytic water splitting. The water oxidation activity of compound 1 exhibits Tafel slope equivalent to 361.48 mV.dec-1 for hydrogen evolution reaction (HER) and 353.53 mV.dec-1 for oxygen evolution reaction (OER) in an alkaline medium while almost similar values of Tafel slope for HER and OER equivalent to 287.33 mV.dec-1 and 289.93 mV.dec-1 respectively in acidic medium. Thus, the compound 1 has excellent efficacy in catalyzing HER and OER in acidic as well as alkaline medium, which is ascribed to its distinctive 3D architecture.

Enhancing hydrogen evolution and oxidation kinetics through oxygen insertion into nickel lattice

Nickel-based materials, including metallic Ni and Ni oxide, have been widely studied in the exploration of non-precious-metal hydrogen electrocatalysts, but neither pure Ni nor NiO is ideal for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). In this paper, an oxygen insertion strategy was applied on nickel to regulate its hydrogen electrocatalytic performance, and the oxygen-inserted nickel catalyst was successfully obtained with the assistance of tungsten dioxide support (denoted as O-Ni/WO2). The partial insertion of oxygen in Ni maintains the face-centered cubic arrangement of Ni atoms, simultaneously expanding the lattice and increasing the lattice spacing. Consequently, the adsorption strength of *H and *OH on Ni is optimized, thus resulting in superior electrocatalytic performance of O-Ni/WO2 in alkaline HER/HOR. The Tafel slope of O-Ni/WO2@NF for HER is 56 mV dec−1, and the kinetic current density of O-Ni/WO2 for HOR reaches 4.85 mA cm−2, which is ahead of most currently reported catalysts. Our proposed strategy of inserting an appropriate amount of anions into the metal lattice could provide more possibilities for the design of high-performance catalysts.

Rational Design of Organic Electrocatalysts for Hydrogen and Oxygen Electrocatalytic Applications.

Efficient electrocatalysts are pivotal for advancing green energy conversion technologies. Organic electrocatalysts, as cost-effective alternatives to noble-metal benchmarks, have garnered attention. However, the understanding of the relationships between their properties and electrocatalytic activities remains ambiguous. Plenty of research articles regarding low-cost organic electrocatalysts started to gain momentum in 2010 and have been flourishing recently though, a review article for both entry-level and experienced researchers in this field is still lacking. This review underscores the urgent need to elucidate the structure-activity relationship and design suitable electrode structures, leveraging the unique features of organic electrocatalysts like controllability and compatibility for real-world applications. Organic electrocatalysts are classified into four groups: small molecules, oligomers, polymers, and frameworks, with specific structural and physicochemical properties serving as activity indicators. To unlock the full potential of organic electrocatalysts, five strategies are discussed: integrated structures, surface property modulation, membrane technologies, electrolyte affinity regulation, and addition of anticorrosion species, all aimed at enhancing charge efficiency, mass transfer, and long-term stability during electrocatalytic reactions. The review offers a comprehensive overview of the current state of organic electrocatalysts and their practical applications, bridging the understanding gap and paving the way for future developments of more efficient green energy conversion technologies.

Augmenting the Electrocatalytic Activities of Metal–N-Heterocyclic Carbene Complexes as Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution Reactions by Carbon Composite Strategy

Augmenting the Electrocatalytic Activities of Metal–N-Heterocyclic Carbene Complexes as Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution Reactions by Carbon Composite Strategy

Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density.

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50V to deliver the current density of 10mAcm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200mAcm-2 at a low cell voltage of 1.78V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Functionality Modulation Toward Thianthrene-based Metal-Free Electrocatalysts for Water Splitting.

The development of metal-free bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is significant but rarely demonstrated. Porous organic polymers (POPs) with well-defined electroactive functionalities show superior performance in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Precise control of the active sites' local environment requires careful modulation of linkers through the judicious selection of building units. Here, a systematic strategy is introduced for modulating functionality to design and synthesize a series of thianthrene-based bifunctional sp2 C═C bonded POPs with hollow spherical morphologies exhibiting superior electrocatalytic activity. This precise structural tuning allowed to gain insight into the effects of heteroatom incorporation, hydrophilicity, and variations in linker length on electrocatalytic activity. The most efficient bifunctional electrocatalyst THT-PyDAN achieves a current density of 10 mA cm─2 at an overpotential (η10) of ≈65 mV (in 0.5 m H2SO4) and ≈283 mV (in 1 m KOH) for HER and OER, respectively. THT-PyDAN exhibits superior activity to all previously reported metal-free bifunctional electrocatalysts in the literature. Furthermore, these investigations demonstrate that THT-PyDAN maintains its performance even after 36 h of chronoamperometry and 1000 CV cycling. Post-catalytic characterization using FT-IR, XPS, and microscopic imaging techniques underscores the long-term durability of THT-PyDAN.

NiSe-modified CoMoO4 nanosheets as bifunctional electrocatalysts for hydrogen and oxygen evolution reactions

Selecting self-supporting substrates with large specific surface areas is an effective strategy to avoid the agglomeration of nanomaterials and improve the structural stability of materials while increasing their electrical conductivity. In this study, CoMoO4 nanosheet structures were first grown on a nickel foam (NF) substrate by hydrothermal and calcination processes. Then, NiSe nanoparticles were deposited on NF/CoMoO4 by a constant potential method to construct NF/CoMoO4 @NiSe nanosheet electrode materials with graded layered structures. This nanosheet structure grown on NF substrates provided enough space for mass transfer and fully exposed the electrochemical active sites. Meanwhile, the self-supported electrode reduced the indirect contact resistance between the electrocatalyst and the substrate, which promoted the timely release of generated bubbles from the electrode. The NF/CoMoO4 @NiSe electrode exhibited excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities under alkaline conditions. Overpotentials of only 58 mV and 184 mV were needed to achieve a current density of 10 mA·cm−2 for the HER and OER, respectively. This study presents new ideas for the construction of nanosheet structures and the design of efficient HER and OER bifunctional electrocatalysts using transition metal selenides.

Correction: Spent tea leaves templated synthesis of highly active and durable cobalt-based trifunctional versatile electrocatalysts for hydrogen and oxygen evolution and oxygen reduction reactions

Correction for ‘Spent tea leaves templated synthesis of highly active and durable cobalt-based trifunctional versatile electrocatalysts for hydrogen and oxygen evolution and oxygen reduction reactions’ by Md Ariful Ahsan et al., Green Chem., 2020, 22, 6967–6980, https://doi.org/10.1039/D0GC02155E.

Hydrothermally synthesized double layered ferrite and its CNTs anchored nanoarchitecture: A novel water splitting electrocatalyst

In this study, NiO, NiFe2O4 (NF), NiFe2O4-LDH, and NiFe2O4-LDH@CNTs electrocatalysts were made using a combination of ultrasonication and hydrothermal methods. Electrocatalysts's structure and crystalline phase were confirmed using X-ray diffraction, while their shape and texture were analyzed using electronic study. Electrochemical investigations, like impedance, linear sweep, and cyclic voltammetry, were used to evaluate the catalysts's electrocatalytic activities. The NF-LDH@CNTs-based electrocatalyst showed superior hydrogen and oxygen evaluation activity than the counterpart electrocatalysts. The NF-LDH@CNTs electrocatalyst had a high electrolytic potential, as its onset potential (1.533 V) and over-potential (303 mV) were low. It was also seen that the nanocomposite had a lower Tafel slope (0.26 V) than other electrocatalysts, which shows that NF-LDH@CNTs are good at transporting electrons. The newly created composite of carbon nanotubes (CNTs) and layered double hydroxides (LDH) presents a cost-effective and effective substitute for metal-based electrocatalysts for hydrogen & oxygen evaluation.

Construction of Ni2P-MoC/Coal-Based Carbon Fiber Self-Supporting Catalysts for Enhanced Hydrogen Evolution.

Efficient and inexpensive electrocatalysts play an important role in the hydrogen evolution reaction (HER) of electrolytic water splitting. Herein, Ni2P-MoC/coal-based carbon fiber (Ni2P-MoC/C-CF) self-supporting catalysts were obtained by low-temperature phosphorization and high-temperature carbonization. The Mo source and oxidized coal were uniformly dispersed in the carbon support by electrospinning technology. A precursor of Ni was introduced by the impregnation method. The synergistic effect of MoC and Ni2P may reduce the strong hydrogen adsorption capacity of pure MoC and provide a fast hydrogen release process. In addition, the C-CFs prepared by electrospinning can not only prevent the agglomeration of MoC and Ni2P particles at a high temperature but also provide a self-supporting support for the catalyst. As a result, the catalytic performance of the HER was improved greatly, and a low overpotential of 112 mV at 10 mA cm-2 was exhibited stably by the Ni2P-MoC/C-CFs. This work not only converts coal into coal-based carbon materials but also provides a feasible pathway for the rational design of large-scale molded hydrogen electrocatalysts.

Non-Noble Transition Metal-Based Electrocatalysts for Green Hydrogen Production from Anion Exchange Membrane (AEM) Seawater Electrolyzer

As water-scarce is increasing rapidly all over the world, water electrolysis might not be a practical approach for sustainable hydrogen production in the long term. Fortunately, hydrogen production from the anion exchange membrane (AEM) seawater electrolysis enables to achieve of sustainability and durability. But still, suitable electrocatalysts for hydrogen and oxygen evolution reactions in seawater are not figured out yet. Here we report non-noble transition metal-based electrocatalysts for hydrogen and oxygen evolution reaction in seawater electrolysis. The synthesized electrocatalysts were in-situ characterized in X-ray diffraction (XRD), scanning electron microscopy (SEM), Transition electron microscopy (TEM), Raman spectroscopy, and ex-situ characterized in linear sweep voltammetry (LSV), Chronopotentiometry, and impedance studies. Further, the electrocatalysts were investigated in a single-cell anion exchange membrane electrolyzer, and polarization curves, stability tests, and efficiency calculations were carried out. These research findings will be further investigated until attains the industrially required parameters of 1 A cm-2 at a low overpotential of 1.8 V.

A Review of the Recent Advances in Development of Noble Metal‐Free Materials as Electrocatalysts for Hydrogen and Oxygen Evolution Reactions

AbstractSustainable energy development can no longer be met by fossil fuels alone. Hence, electrochemical water splitting containing oxygen and hydrogen evolution reactions is appealing as a clean energy pathway. As respects the water splitting efficiency which is largely determined by the selectivity, durability, and intrinsic activity of the electrocatalysts, one of the most challenging questions when studying these materials is “which category of electrocatalysts will show the best performance in this issue?” The best electrocatalysts for water splitting still come from noble metals. Although these materials show particularly good efficiency, but due to the scarce resources their massive use is limited. Therefore, the noble metal‐free materials due to their stability, efficiency, abundance and variety of reaction sites were introduced as an interesting candidate for electrochemical water splitting reactions. In this review, based on the important above‐mentioned points, our attention was focused on key categories based on transition metals (TMs), metal organic framework derived (MOF‐derived), carbon‐based hybrids, graphitic carbon nitride (g‐C3N4) hybrids, and bio‐assisted electrocatalysts. These compounds have shown significant activity and stability for broad electrocatalysis applications in water splitting reactions and displaying remarkable potential to replace with noble metal‐based catalysts. This comprehensive review identifies rational strategies for designing and synthesizing high‐performance novel noble metal‐free electrocatalysts for water splitting.

Design and synthesis of Ni-Co-X(X = O, S, P)/Co(OH)2 core/shell layered nanosheets as multifunctional electrodes for hydrogen electrocatalysts and supercapacitors

The requirements of the morphology and material properties in common make it possible to integrate the two functional electrodes, hydrogen electrocatalyst and supercapacitor, into one material system. The order of electrochemical performance of core materials was ranked as NiCoP > NiCo2S4 > NiCo2O4. By constructing core/shell heterostructure, Ni-Co-X/Co(OH)2 composites achieved the boost of electrochemical performance than individual Ni-Co-X. Particularly, the NiCoP/Co(OH)2 composite synthesized under optimal conditions presented both excellent catalytic activity and charge storage capability. The NiCoP/Co(OH)2 composite needed small overpotential of 73 mV to drive current density of 10 mA cm−2 in 1 M KOH, displayed Tafel slope of 75 mV dec−1 and long-term stability over 15 h without obvious fluctuation. Moreover, the NiCoP/Co(OH)2 composite showed high specific capacitance of 1604 F g−1 at 1 A g−1, delivered remarkable rate capability of 81.8 % at 20 A g−1 and cyclic stability with 91.8 % capacity retention over 5000 cycles. The impressive electrochemical properties of NiCoP/Co(OH)2 composite is attributed to the enriched active sites, enhanced electronic conductivity and strong synergistic effect. Our research provides insights and effective strategies for the design and synthesis of integrated electrodes for hydrogen electrocatalysts and supercapacitors.

Toward rational design of dual-metal-site single atom electrocatalysts for hydrogen and oxygen evolution reactions

Dual-metal-site catalysts (DMSCs) have emerged as a frontier in the field of heterogeneous catalysis due to they can improve the original structure catalytic performances of water splitting, including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the effective DMSCs for HER and OER is still lacking due to their limited activity and complex electronic interactions of metal sites. Here, the HER and OER activities of 12 DMSCs and 6 single-metal-site catalysts (SMSCs) are investigated by density functional theory (DFT) calculations. It is found that N4-coordinated DMSCs and SMSCs exhibit better OER performance than that with N3-coordinated structures, in which Fe/Co-N4-a-Fe-Gr and Co/Ni-N4-a-Ni have the best OER and HER performances, with the corresponding ηOER and ΔGH* are 0.32 V and −0.02 eV, respectively. In addition, strong linear relationships are found between ΔG*O and ΔG*OH, ΔG*OOH and ΔG*OH (correlation coefficient, R2 almost equal to 1). There is a significant volcanic curve and a strong linear relationship between the metal-loaded d-band center (εd) and ηOER, εd and ΔG*OH in N4-coordinated DMSCs, respectively. The dynamics simulations results indicated that most of DMSCs are dynamically stable at reaction temperature.

Antimony oxides-protected ultrathin Ir-Sb nanowires as bifunctional hydrogen electrocatalysts

Antimony oxides-protected ultrathin Ir-Sb nanowires as bifunctional hydrogen electrocatalysts

Water Splitting as an Alternative for Electrochemical Hydrogen and Oxygen Generation: Current Status, Trends, and Challenges

Water splitting technology is an innovative strategy to face the dependency on fossil fuels and, at the same time, address environmental pollution issues. Electrocatalysts seem to be the better option to improve water separation efficiency and satisfy the commercial-scale demand for hydrogen. Therefore, the design and fabrication of heterostructures with a high affinity for achieving water splitting have been proposed. In this review, the application of several electrocatalysts for hydrogen and oxygen evolution reactions is presented and discussed in detail. A review of the recent advances in water separation using noble metals such as Pt-, Ir-, and Ru-based electrodes is presented, followed by a highlighting of the current trends in noble-metal-free electrocatalysts and novel preparation methods. Furthermore, it contemplates some results of a hybrid organic molecule–water electrolysis and photoelectrochemical water splitting. This review intends to give insight into the main trends in water splitting and the barriers that need to be overcome to further boost the efficiency of the main hydrogen and oxygen generation systems that ultimately result in large-scale applications. Finally, future challenges and perspectives are addressed, considering all the novelties and the proposed pathways for water splitting.