Electrocatalysts For Hydrogen Research Articles

Designing In Situ Grown Ternary Oxide/2D Ni-BDC MOF Nanocomposites on Nickel Foam as Efficient Electrocatalysts for Electrochemical Water Splitting

The security of future energy, hydrogen, is subject to designing high-performance, stable, and low-cost electrocatalysts for hydrogen and oxygen evolution reactions (HERs and OERs), for the realization of efficient overall water splitting. Two-dimensional (2D) metal–organic frameworks (MOFs) introduce a large family of materials with versatile chemical and structural features for a variety of applications, such as supercapacitors, gas storage, and water splitting. Herein, a series of nanocomposites based on NCM/Ni-BDC@NF (N═Ni, C═Co, M:F═Fe, C═Cu, and Z═Zn, BDC: benzene dicarboxylic acid, NF: nickel foam) were directly developed on NF using a facile yet scalable solvothermal method. After coupling, the electronic structure of metallic atoms was well-modulated. Based on the XPS results, for the NCF/Ni-BDC, cationic atoms shifted to higher oxidation states, favorable for the OER. Conversely, for the NCZ/Ni-BDC and NCC/Ni-BDC nanocomposites, cationic atoms shifted to lower oxidation states, advantageous for the HER. The as-prepared NCF/Ni-BDC demonstrated prominent OER performance, requiring only 1.35 and 1.68 V versus a reversible hydrogen electrode to afford 10 and 50 mA cm–2 current densities, respectively. On the cathodic side, NCZ/Ni-BDC exhibited the best HER activity with an overpotential of 170 and 350 mV to generate 10 and 50 mA cm–2, respectively, under 1.0 M KOH medium. In a two-electrode alkaline electrolyzer, the assembled NCZ/Ni-BDC (cathode) ∥ NCF/Ni-BDC (anode) couple demanded a cell voltage of only 1.58 V to produce 10 mA cm–2. The stability of NCF/Ni-BDC toward OER was also exemplary, experiencing a continuous operation at 10, 20, and 50 mA cm–2 for nearly 45 h. Surprisingly, the overpotential after OER stability at 50 mA cm–2 dropped drastically from 450 to 200 mV. Finally, the faradaic efficiencies for the overall water splitting revealed the respective values of 100 and 85% for the H2 and O2 production at a constant current density of 20 mA cm–2.

Electrodeposition of Ni - Fe on graphite rod as an efficient and binder-free electrocatalyst for oxygen and hydrogen evolution reactions

In this paper, nickel-iron (Ni-Fe) on a graphite substrate was electrodeposited as an effective electrocatalyst for hydrogen and oxygen evolution reactions using the cyclic voltammetry method for the first time. Some important factors such as the range of applied potential, scan rate, and the number of cycles were optimized. In addition, the used substrate is a graphite rod, which is cheap, stable, and has good electrical conductivity. The main results show that the improved Ni-Fe coating on graphite rod has promising hydrogen evolution reaction (HER) activity, which exhibits small over voltages of − 191.2, − 394.0, and − 687.3 mV at the current densities of − 10, − 100, and − 400 mA. cm−2, respectively. Furthermore, the synthesized Ni-Fe electrocatalyst only needs 284 mV overpotentials to operate at a current density of 10 mA. cm−2, indicating its great performance for the oxygen evolution reaction (OER). This paper offers a method for generating a bifunctional, binder-free, affordable, and fast water splitting electrocatalyst that has excellent performance.

Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

AbstractA novel strategy utilizing high‐frequency (10 MHz) hybrid sound waves to dramatically enhance hydrogen evolution reactions (HER) in notoriously difficult neutral electrolytes by modifying their network coordination state is presented. Herein, the practical limitations associated with existing electrolyzer technology is addressed, including the need for highly corrosive electrolytes and expensive electrocatalysts, by redefining conceptually‐poor hydrogen electrocatalysts in neutral electrolytes. The improvement in HER performance is attributed to the unique capability of the intense local electromechanical coupling arising from the acoustic‐forcing to ‘frustrate’ the tetrahedrally‐coordinated hydrogen bond network of water molecules at the electrode–electrolyte interface, resulting in the generation of a high concentration of “free” water molecules that are more readily able to access catalytic sites on the unmodified polycrystalline electrode. Together with the other synergistic effects that accompany the acoustic excitation (e.g., hydronium ion generation, convective relaxation of diffusion mass transfer limitations, and prevention of bubble build‐up and their removal from the electrode), the resultant overpotential reduction of 1.4 V at −100 mA cm−2 and corresponding 14‐fold increase in current density, together with a net‐positive energy saving of 27.3%, showcases the potential of the technology as a scalable platform for effectively enhancing the efficiency of green hydrogen production.

Interface Metal Oxides Regulating Electronic State around Nickel Species for Efficient Alkaline Hydrogen Electrocatalysis.

Heterogeneous electrocatalysis typically depends on the surface electronic states of active sites. Modulating the surface charge state of an electrocatalysts can be employed to improve performance. Among all the investigated materials, nickel (Ni)-based catalysts are the only non-noble-metal-based alternatives for both hydrogen oxidation and evolution reactions (HOR and HER) in alkaline electrolyte, while their activities should be further improved because of the unfavorable hydrogen adsorption behavior. Hereto, Ni with exceptional HOR electrocatalytic performance by changing the d-band center by metal oxides interface coupling formed in situ is endowed. The resultant MoO2 coupled Ni heterostructures exhibit an apparent HOR activity, even approaching to that of commercial 20% Pt/C benchmark, but with better long-term stability in alkaline electrolyte. An exceptional HER performance is also achieved by the Ni-MoO2 heterostructures. The experiment results are rationalized by the theoretical calculations, which indicate that coupling MoO2 with Ni results in the downshift of d-band center of Ni, and thus weakens hydrogen adsorption and benefits for hydroxyl adsorption. This concept is further proved by other metal oxides (e.g., CeO2 , V2 O3 , WO3 , Cr2 O3 )-formed Ni-based heterostructures to engineer efficient hydrogen electrocatalysts.

Role of Ni in PtNi Bimetallic Electrocatalysts for Hydrogen and Value-Added Chemicals Coproduction via Glycerol Electrooxidation.

Pt-based bimetallic electrocatalysts are promising candidates to convert surplus glycerol from the biodiesel industry to value-added chemicals and coproduce hydrogen. It is expected that the nature and content of the elements in the bimetallic catalyst can not only affect the reaction kinetics but also influence the product selectivity, providing a way to increase the yield of the desired products. Hence, in this work, we investigate the electrochemical oxidation of glycerol on a series of PtNi nanoparticles with increasing Ni content using a combination of physicochemical structural analysis, electrochemical measurements, operando spectroscopic techniques, and advanced product characterizations. With a moderate Ni content and a homogenously alloyed bimetallic Pt-Ni structure, the PtNi2 catalyst displayed the highest reaction activity among all materials studied in this work. In situ FTIR data show that PtNi2 can activate the glycerol molecule at a more negative potential (0.4 V RHE) than the other PtNi catalysts. In addition, its surface can effectively catalyze the complete C-C bond cleavage, resulting in lower CO poisoning and higher stability. Operando X-ray absorption spectroscopy and UV-vis spectroscopy suggest that glycerol adsorbs strongly onto surface Ni(OH) x sites, preventing their oxidation and activation of oxygen or hydroxyl from water. As such, we propose that the role of Ni in PtNi toward glycerol oxidation is to tailor the electronic structure of the pure Pt sites rather than a bifunctional mechanism. Our experiments provide guidance for the development of bimetallic catalysts toward highly efficient, selective, and stable glycerol oxidation reactions.

CuZr Metal Glass Powder as Electrocatalysts for Hydrogen and Oxygen Evolution Reactions

For the practical application of water electrolysis, it is essential to develop cost-effective and high efficiency electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evaluation reaction (OER). In this work, we applied CuZr metallic glass powder, after chemical dealloying treatment, as electrocatalysts. The as-prepared sample had both the increased specific area and optimized surface composition of an efficient catalyst. During the HER and OER processes, the dealloyed CuZr sample displayed overpotential of 195 mV and 310 mV at current density of 10 mA cm−2, respectively. A two-electrode water splitting cell, using the as-prepared CuZr sample, exhibited high stability towards a high current density of 500 mA cm−2, and lower overpotential, compared to a Pt/C//IrO2 cell, during the 10 mA cm−2 constant current density aging test.

Engineering Amorphous/Crystalline Rod-like Core-Shell Electrocatalysts for Overall Water Splitting.

The design of bifunctional electrocatalysts for hydrogen and oxygen evolution reactions delivering excellent catalytic activity and stability is highly desirable, yet challenged. Herein, we report an amorphous RuO2-encapsulated crystalline Ni0.85Se nanorod structure (termed as a/c-RuO2/Ni0.85Se) for enhanced HER and OER activities. The as-prepared a/c-RuO2/Ni0.85Se nanorods not only demonstrate splendid HER activity (58 mV@10 mA cm-2 vs RHE), OER activity (233 mV@10 mA cm-2 vs RHE), and electrolyzer activity (1.488 V@10 mA cm-2 vs RHE for overall water splitting) but also exhibit long-term stability with negligible performance decay after 50 h continuous test for overall water splitting. In addition, the variation of the d-band center (from the perspective of bonding and antibonding states) is unveiled theoretically by density functional theory calculations upon amorphous RuO2 layers coupling to clarify the increased hydrogen species adsorption for HER activity enhancement. This work represents a new pathway for the fabrication of bifunctional electrocatalysts toward green hydrogen generation.

Co/CoS2 heterojunction embedded in nitrogen-doped carbon framework as bifunctional electrocatalysts for hydrogen and oxygen evolution

The construction of efficient and stable non-noble metal bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) presents a challenge in electrocatalytic water splitting. CoS2 is a promising electrocatalyst that could replace precious metals. In this work, a series of Co-MOF precursors having average particle sizes ranging from the nanometer to the micron scale (86–1084 nm) were synthesized in an unprecedented attempt; Co/CoS2 heterojunction embedded in nitrogen doped carbon framework (Co/CoS2@NC) was prepared through further carbonization and sulfurization. The samples were characterized and evaluated by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The results indicate that when the size of Co-MOF is less than 300 nm, the cubic structure framework easily collapses to form the spherical structure during the carbonization process. The catalytic activity of Co@NC is size-dependent; Co/CoS2@NC exhibited the best performance among the series, with an overpotential of 188 mV for HER and 349 mV for OER at a current density of 10 mA cm−2. This work provides experimental guidance for the design and synthesis of low-cost, efficient, and robust Co-based electrocatalysts.

Facile electrochemical synthesis of Ni-Sb nanostructure supported on graphite as an affordable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

• A novel Ni-Sb nanostructure as a bifunctional electrocatalyst was fabricated by a facile electrodeposition method. • The Ni-Sb nanostructure exhibited outstanding activity and long-term stability toward HER and OER performances. • The unique morphology and the synergistic effect between Ni and Sb elements are responsible for the best electrocatalytic characteristics. • Sb with a 2D layered structure improves the conductivity and charge transfer ability of electrodes. The design of bifunctional electrocatalysts with high activity and long-term stability is essential for water splitting systems. Herein, a binder-free and cost-effective Ni-Sb nanostructured catalyst was prepared using the one-step electrodeposition method from an organic solution, and its electrochemical characteristics for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium were studied. The optimized Ni-Sb electrode demonstrated the best electrocatalytic activity for hydrogen and oxygen evolution reactions. Benefiting from the unique morphology, super-hydrophilic properties, and the synergistic effect between Ni and Sb elements, low overpotentials of 158 mV and 367 mV are needed to produce a current density of 10 mA.cm −2 for HER and OER, respectively. Noteworthy, the Ni-Sb bifunctional catalyst displayed enhanced electrocatalytic stability at a current density of 100 mA.cm −2 and works for 60,000 s. Our experimental data based on the electrochemical impedance spectroscopy (EIS) measurements before and after the stability test confirmed that the optimized electrode retains its catalytic performances for HER and OER owing to high conductivity and fast charge transfer. This study thus provides helpful avenues to design new antimonide-based catalysts for various applications.

Regulating the Surface Electronic Structure of RuNi Alloys for Boosting Alkaline Hydrogen Oxidation Electrocatalysis

Nickel (Ni) is a promising electrocatalyst for alkaline hydrogen oxidation reaction (HOR). However, the strong hydrogen binding at Ni site (Ni–H) limits its electrocatalytic HOR activity. Herein, ruthenium (Ru) is introduced to regulate the surface electronic structure of Ni and optimize the Ni–H. Simultaneously, constructing the interfacial-oxygen (O) configuration endows Ni with suitable oxophilic components to optimize the adsorption energy for surface hydroxyl species (OH*). The density functional theory (DFT) simulation and characterization results confirm that electron transfer from Ni to Ru causes the d-band center of Ni to shift down, weakening the hydrogen binding energy (HBE) and hydroxyl binding energy (OHBE), which synergistically contributes the enhanced HOR performance for the optimal O-RuNi@C-400 with a diffusion-limiting current density of 2.87 mA cm–2 and mass activity of 601 mA mg–1PGM at an overpotential of 50 mV, which is ∼1.20 and 7.90 times higher than that of Pt/C, respectively. Besides, because of the protective shell of oxophilic Ni–O–C interface to reduce the affinity with CO, O-RuNi@C-400 exhibits better CO tolerance (1000 ppm) than that of commercial Pt/C in alkaline media, making it a promising HOR electrocatalyst for hydrogen fuel cells.

Polymorphic ternary metal chalcogenide solid solution nanopowder as electrocatalyst for hydrogen and oxygen evolution reaction

Here, in this work, a novel synthesis route of polymorphic FexNi1-xSe2 nanopowders consisting of nanoparticles and nanorods for x = 0.2–0.8 has been investigated by a simple hydrothermal process. Coral shaped NiSe2 (x = 0) and nanorod structured FeSe2 (x = 1) are in pure cubic and orthorhombic phase, respectively whereas FexNi1-xSe2 solid solution nanopowder is a combination of both. After important basic characterizations, electrochemical hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) are carried out using FexNi1-xSe2 as cathode and anode, respectively. Among all the variations, x = 0.4 has exhibited the highest HER activity with low overpotential of −106 mV for 10 mA/cm2 in acidic medium and x = 0.2 is the most efficient as anode in OER in alkaline medium with overpotential of 280 mV to drive the current density of 10 mA/cm2 with a small amount of oxidation. Long term stability is achieved without any degradation for both HER and OER in extreme pH for FexNi1-xSe2. The insertion of Fe in the lattice of NiSe2 has improved the conductivity thereby increasing the charge transfer phenomenon. The coexistence of two different morphologies for the optimum ratio of Fe/Ni has generated more active sites participating in the electrochemical reactions. The easy oxidation of catalysts during OER can be restricted by the polymorphic crystal structure of FexNi1-xSe2.

Unlocking Interfacial Electron Transfer of Ruthenium Phosphides by Homologous Core-Shell Design toward Efficient Hydrogen Evolution and Oxidation.

Developing high-efficiency electrocatalysts for the hydrogen evolution and oxidation reactions (HER/HOR) in alkaline electrolytes is of critical importance for realizing renewable hydrogen technologies. Ruthenium phosphides (RuPx ) are promising candidates to substitute Pt-based electrodes; however, great challenges still remain in their electronic structure regulation for optimizing intermediate adsorption. Herein, it is reported that a homologous RuP@RuP2 core-shell architecture constructed by a phosphatization-controlled phase-transformation strategy enables strong electron coupling for optimal intermediate adsorption by virtue of the emergent interfacial functionality. Density functional theory calculations show that the RuP core and RuP2 shell present efficient electron transfer, leading to a close to thermoneutral hydrogen adsorption Gibbs free energy of 0.04eV. Impressively, the resulting material exhibits superior HER/HOR activities in alkaline media, which outperform the benchmark Pt/C and are among the best reported bifunctional hydrogen electrocatalysts. The present work not only provides an efficient and cost-effective bifunctional hydrogen electrocatalyst, but also offers a new synthetic protocol to rationally synthesize homologous core-shell nanostructures for widespread applications.

Design of metal‐substituted tungsten diboride as an efficient bifunctional electrocatalyst for hydrogen and oxygen evolution

Design of metal‐substituted tungsten diboride as an efficient bifunctional electrocatalyst for hydrogen and oxygen evolution

Pt-Based High-Entropy Alloy Nanoparticles as Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution

Pt-Based High-Entropy Alloy Nanoparticles as Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution

Amine and Carbon-pretreated nickel–molybdenum disulfide as bifunctional electrocatalysts for hydrogen and oxygen gas evolution

We report the synthesis and characterization of a variety of nickel molybdenum disulfide (NiMoS2) materials as efficient bifunctional electrocatalysts for both the hydrogen evolution and oxygen evolution reactions (HER and OER, respectively). These catalysts were obtained from pretreated ammonium tetrathiomolybdate (ATM) using ethylenediamine (EDA), diethylenetriamine (DETA), or carbon nanotubes (CNT), which were further reacted with Ni(NO3)2. All the materials were characterized by scanning electron microscopy (SEM) and powder X-ray diffraction (pXRD), and all materials were evaluated as both HER and OER electrocatalysts. The NiMoS2 synthesized from DETA-pretreatment exhibits the best HER catalytic performance with the lowest overpotential of 0.151 V, while the CNT-modified NiMoS2 shows the lowest OER overpotential of 0.310 V. All the pretreated NiMoS2 electrocatalysts show significantly improved catalytic activity compared to the one prepared directly from pristine ATM precursor.

Djurleite Copper Sulfide-Coupled Cobalt Sulfide Interface for a Stable and Efficient Electrocatalyst.

Transition metal sulfides (TMS) exhibit proliferated edge sites, facile electrode kinetics, and improved intrinsic electrical conductivity, which demand low potential requirements for total water splitting application. Here, we have propounded copper sulfide-coupled cobalt sulfide nanosheets grown on 3D nickel as an electrocatalyst for hydrogen (HER) and oxygen evolution (OER) reactions. The formation of djurleite copper sulfide with a Cu vacancy enables faster H+ ion transport and shows improved HER activity with a remarkably lower overpotential of 164 mV at 10 mA/cm2, whereas cobalt-incorporated copper sulfide undergoes cation exchange during synthesis and shows elevated OER activity with a lower overpotential of 240 mV at 10 mA/cm2 for the OER. Moreover, Cu2-xS/Co is said to have a hybrid CoS-CoS2 interface and provide Co2+ active sites on the surface and enable the fast adsorption of intermediate species (OH*, O*, and OOH*), which lowers the potential requirement. The copper vacancy and cation exchange with a hybrid CoS-CoS2 structure are helpful in supplying more surface reactive species and faster ion transport for the HER and OER, respectively. The full-cell electrolyzer requires a very low potential of 1.58 V to attain a current density of 10 mA/cm2, and it shows excellent stability for 50 h at 100 mA/cm2 as confirmed by the chronopotentiometry test.

Janus bimetallic materials as efficient electrocatalysts for hydrogen oxidation and evolution reactions

The development of hydrogen energy is limited by the high cost of platinum group metals (PGM). There is an urgent need to design efficient PGM-free electrocatalysts in the hydrogen electrode. Herein, Janus Ni/W bimetallic materials are proposed as an effective PGM-free bifunctional hydrogen electrocatalyst. By constructing the bimetallic materials, a synergistic effect is realized to enhance the reaction kinetics and improve the catalytic performance. In general, Ni can provide excellent Had sites, and W serves as OHad sites. Therefore, the synergistic effect of Ni and W can improve the kinetics of hydrogen evolution reaction and the hydroxide oxidation reaction. Ni/W@NF can obtain the hydrogen evolution reaction current density of 10 mA cm−2 with an overpotential of only 62.6 mV, and the exchange current density of hydroxide oxidation reaction can reach 1.83 mA cm−2. This work provides a new idea for the design of high-efficiency and low-cost PGM-free bifunctional hydrogen electrocatalysts.

Electrodeposition of Ni nanoparticles from deep eutectic solvent and aqueous solution promoting high stability electrocatalyst for hydrogen and oxygen evolution reactions

Nanostructured Ni films were synthesized from two distinct baths and were assessed as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH. Herein, Ni was electrodeposited from two separate solvents, the aqueous acetate buffer and ethaline solvent as a kind of deep eutectic solvents (DESs), and both the deposited films were investigated as electrocatalysts for HER and OER. The electrodeposition parameters such as pH and deposition potential were studied. The electrodeposition process was performed using chronoamperometry technique and Ni deposits were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Fabricated Ni@PGE deposit from ethaline only requires an overpotential of − 154 mV and 350 mV to achieve a current density of 10 mA cm−2 for HER and OER, respectively. While, Ni@PGE from acetate requires an overpotential of − 164 mV and 400 mV to produce the current density of 10 mA cm−2 for HER and OER.Graphical abstract

Scalable synthesis of hcp ruthenium-molybdenum nanoalloy as a robust bifunctional electrocatalyst for hydrogen evolution/oxidation

The hydrogen evolution reaction (HER) is the cathodic process of water splitting, and its reverse, the hydrogen oxidation reaction (HOR), is the anodic process of an H2-O2 fuel cell; both play important roles in the development of hydrogen energy. The rational design and scalable fabrication of low-cost and efficient bifunctional catalysts for the HER/HOR are highly desirable. Herein, ultrasmall Mo-Ru nanoalloy (Mo0.5Ru3 and MoRu3) particles uniformly distributed on mesoporous carbon (MPC) were successfully synthesized by a simple method that is easy to scale up for mass production. After the incorporation of Mo atoms, the as-prepared Mo0.5Ru3 and MoRu3 nanoalloys maintain a hexagonal-close-packed crystal structure. In acidic media, Mo0.5Ru3 exhibits excellent Pt-like HER and HOR activity, as well as good stability. Density functional theory (DFT) calculations reveal that the H adsorption free energy (ΔGH*) on the Mo0.5Ru3 (0 0 1) surface (−0.09 eV) is much closer to zero than that of metallic Ru (−0.22 eV), which contributes to the enhanced catalytic activity. In alkaline media, Mo0.5Ru3 also presents outstanding HER and HOR activity, even significantly outperforming Pt/C. The DFT results confirm that optimal binding energies with H* and OH* intermediate species, and low energy barriers in the water dissociation and formation steps, efficiently accelerate the alkaline HER/HOR kinetics of Mo0.5Ru3. This study provides a new avenue for the scalable fabrication of high-efficiency bifunctional electrocatalysts for the HER and HOR in both acidic and alkaline media.

A Cu3P@NiFe-MOF Hybrid as an Efficient Electrocatalyst for Hydrogen and Oxygen Evolution Reactions

A Cu3P@NiFe-MOF Hybrid as an Efficient Electrocatalyst for Hydrogen and Oxygen Evolution Reactions