Facile route to achieve MoSe2-Ni3Se2 on nickel foam as efficient dual functional electrocatalysts for overall water splitting

Since the catalytic activity of present nickel-based synthetic selenide is still to be improved, MoSe₂-Ni₃Se₂ was synthesized on nickel foam (NF) (MoSe₂-Ni₃Se₂/NF) by introducing a molybdenum source. After the molybdenum source was introduced, the surface of the catalyst changed from a single-phase structure to a multi-phase structure. The catalyst surface with enriched active sites and the synergistic effect of MoSe₂ and Ni₃Se₂ together enhance the hydrogen evolution reactions (HER), the oxygen evolution reactions (OER), and electrocatalytic total water splitting activity of the catalyst. The overpotential of the MoSe₂-Ni₃Se₂/NF electrocatalyst is only 259 mV and 395 mV at a current density of 100 mA/cm² for HER and OER, respectively. MoSe₂-Ni₃Se₂/NF with a two-electrode system attains a current density of 10 mA/cm² at 1.60 V. In addition, the overpotential of HER and OER of MoSe₂-Ni₃Se₂/NF within 80000 s and the decomposition voltage of electrocatalytic total water decomposition hardly changed, showing an extremely strong stability. The improvement of MoSe₂-Ni₃Se₂/NF catalytic activity is attributed to the establishment of the multi-phase structure and the optimized inoculation of the multi-component and multi-interface.     

Nanoscale engineering MoP/Fe2P/RGO toward efficient electrocatalyst for hydrogen evolution reaction

The preparation of hydrogen evolution reaction (HER) electrocatalyst with high catalytic performance is a huge challenge. In this work, we develop a MoP/Fe₂P/RGO composite as a electrocatalyst for HER. The MoP/Fe₂P/RGO exhibits excellent electrocatalytic performance with a Tafel slope and an onset overpotential of 51 mV/dec and 105 mV, respectively. To drive 10 mA/cm², it only requires a small over-potential of 156 mV. The high electrocatalytic HER activity is mainly due to the synergistic effect of MoP and Fe₂P. In addition, the introduction of RGO not only prevents particle aggregation and coalescence during high temperature phosphating, but also improves the conductivity of the catalyst.     

Effect of iron on Ni–Mo–Fe composite as a low-cost bifunctional electrocatalyst for overall water splitting

By increasing demand for hydrogen and oxygen gas for energy and industrial applications, designing a cheap, high-efficiency, and bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) seems necessary. For this purpose Ni–Mo–Fe as a bifunctional electrocatalyst was synthesized by one-step electrodeposition. From this electrocatalyst with optimal composition and current density, a small overpotential of 65, 161 mV for delivering 10, 100 mA/cm² on HER in alkaline media was achieved. As-fabricated electrode exhibited 344,408 mV for delivering 10, 100 mA/cm² in OER. Furthermore, this electrocatalyst shows high stability and negligible degradation in overpotential for HER and OER under long term stability tests in alkaline media. The notable function of As-fabricated Ni–Mo–Fe is due to the synergism effect between Ni, Mo, and Fe element and binder-free structure. Owing to the high-performance and high-stability of Ni–Mo–Fe electrocatalyst under Hydrogen and Oxygen evolution reactions is a candidate for industrial uses in the alkaline electrolyzer.     

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS₂/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm⁻² for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS₂/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.     

Electrodeposited Ni-Co-Sn alloy as a highly efficient electrocatalyst for water splitting

Water splitting to produce hydrogen and oxygen is considered as a feasible solution to solve the current energy crisis. It is highly desirable to develop inexpensive and efficient electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this paper, nanostructured Ni-Co-Sn alloys were electrodeposited on copper foil and the excellent electrocatalytic performances for both HER and OER in alkaline media were achieved. The optimized Ni-Co-Sn electrode shows a low onset overpotential of −18 mV and a small Tafel slope of 63 mV/dec for the HER, comparable to many state-of-the-art non-precious metal HER catalysts. For the OER, it produces an overpotential of 270 mV (1.50 V vs. RHE) at current density of 10 mA/cm², which is better than that of the commercial Ir/C catalyst. In addition to high electrocatalytic activities, it exhibits good stability for both HER and OER. This is the first report that Ni-Co-Sn is served as a cost-effective and highly efficient bifunctional catalyst for water splitting and it will be of great practical value.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

Binder-free bifunctional SnFe sulfide/oxyhydroxide heterostructure electrocatalysts for overall water splitting

Developing robust non-noble catalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is vital for large-scale hydrogen production from electrochemical water splitting. Here, we synthesize Sn- and Fe-containing sulfides and oxyhydroxides anchored on nickel foam (SnFeS_xO_y/NF) using a solvothermal method, in which a heterostructure is generated between the sulfides and oxyhydroxides. The SnFeS_xO_y/NF exhibits low overpotentials of 85, 167, 249, and 324 mV at 10, 100, 500 and 1000 mA cm^?2 for the HER, respectively, and a low overpotential of only 281 mV at 100 mA cm^?2 for the OER. When it serves as both anode and cathode to assemble an electrolyzer, the cell voltage is only 1.69 V at 50 mA cm^?2. The sulfides should be the efficient active species for the HER, while the oxyhydroxides are highly active for the OER. The unique sulfide/oxyhydroxide heterostructure facilitates charge transfer and lowers reaction barrier, thus promoting electrocatalytic processes.     

Potentiostatic electrodeposited of Ni–Fe–Sn on Ni foam served as an excellent electrocatalyst for hydrogen evolution reaction

Ni–Fe–Sn electrocatalyst supported on nickel foam (Ni–Fe–Sn/NF) with high efficiency of hydrogen evolution reaction (HER) has been successfully fabricated through one-step potentiostatic electrodeposition route. The optimized Ni–Fe–Sn/NF displayed an extremely low overpotential of, respectively, 144 and 180 mV at 50 and 100 mA cm^?2 for HER in alkaline condition. Moreover, it could retain its superior stability for at least 12 h. The remarkable electrocatalytic activity of our electrocatalyst is ascribed to the high conductivity originated from synergistic effects between Ni, Fe, and Sn during HER process.     

Nitrogen-doped carbon active sites boost the ultra-stable hydrogen evolution reaction on defect-rich MoS2 nanosheets

It remains highly challenging to deploy noble-metal-free technologies for commercial hydrogen evolution reaction (HER) catalytic application. A facile strategy is developed in this work to boost the HER activity on non-noble MoS₂ catalyst by taking advantage of the platinum-like behavior of nitrogen doped carbon (CN) active sites for catalyzing the process from H⁺ to H atom. By doping trace amount of CN with the defect-rich MoS₂ nanosheet catalyst, the HER activity is significantly improved with the onset HER overpotential reduced to 50 mV, close to the value observed for the platinum catalyst, and the operational overpotential at 10 mA/cm² decreases by 65 mV. More importantly, with graphite as the counter electrode, stability of the catalyst is substantially improved. No activity decay is detected after 4000 cycles of cyclic voltammetry (CV) sweeping while the overpotential increment of the prisitine MoS₂/C catalyst after 2000 cycles CV sweeping is high to ca. 15 mV.     

Three-dimensional structure of WS2/graphene/Ni as a binder-free electrocatalytic electrode for highly effective and stable hydrogen evolution reaction

Tungsten disulfide (WS₂) has attracted much attention as the promising electrocatalyst for hydrogen evolution reaction (HER). Herein, the three-dimensional (3D) structure electrode composed of WS₂ and graphene/Ni foam has been demonstrated as the binder-free electrode for highly effective and stable HER. The overpotential of 3D WS₂/graphene/Ni is 87 mV at 10 mA cm^?2, and the current density is 119.1 mA cm^?2 at 250 mV overpotential, indicating very high HER activity. Moreover, the current density of 3D WS₂/graphene/Ni at 250 mV only decreases from 119.1 to 110.1 mA cm^?2 even after 3000 cycles, indicating a good stability. The high HER performance of 3D WS₂/graphene/Ni binder-free electrode is superior than mostly previously reported WS₂-based catalysts, which is attributed to the unique graphene-based porous and conductive 3D structure, the high loading of WS₂ catalysts and the robust contact between WS₂ and 3D graphene/Ni backbones. This work is expected to be beneficial to the fundamental understanding of both the electrocatalytic mechanisms and, more significantly, the potential applications in hydrogen economy for WS₂.     

Functionalization of Mn2O3/PdO/ZnO electrocatalyst using organic template with accentuated electrochemical potential toward water splitting

In a broad spectrum of renewable energy technologies, nonprecious, cheap, and robust electrocatalytic material is the fundamental element for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, designing high-efficiency catalysts to match industrial requirements remains a significant challenge. An Efficient and stable OER catalyst [Mn₂O₃/PdO/ZnO] was prepared by a simple and cost-effective facile synthesis approach using metal acetates with the organic extract. The carbonaceous material help in improving the surface area and lowering the band gap energy (2.2 eV) of the Mn₂O₃/PdO/ZnO suggesting the enhanced electrochemical conductivity of synthesized nanomaterial. The catalyst was loaded on Ni-foam and has been tested for Oxyge evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline medium. The material shows higher activity toward OER with a low overpotential and Tafel slope value of 93 mV/dec at a bias of 1.65 V to achieve a current density of 10 mA/cm². The material exhibited an overpotential of 57 mV and Tafel value of 244 mV/dec toward HER which were not much satisfactory. The material offer an overpotential value of 422 mV toward OER which remains consistent even after 2000 cycle in 1M KOH electrolyte. In addition, chronoamperometry test also revealed constant oxygen evolution over 24 hours without any loss in activity. Thus the synthesized bio-fabricated composite material is simple and scalable for widespread use in renewable energy harvesting applications.     

Bifunctional nanoporous ruthenium-nickel alloy nanowire electrocatalysts towards oxygen/hydrogen evolution reaction

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm^?2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm^?2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm^?2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts.     

3D self-standing grass-like cobalt phosphide vesicles-decorated nanocones grown on Ni-foam as an efficient electrocatalyst for hydrogen evolution reaction

The growing hydrogen consumption has greatly promoted the development of efficient, stable and low-cost electrocatalysts for the hydrogen evolution reaction (HER). Constructing functional nanostructures is an efficacious strategy to optimize catalytic performance. Herein, we present a feasible route to fabricate distinctive 3D grass-like cobalt phosphide nanocones clad with mini-vesicles on the hierarchically porous Ni foam, which can directly serve as a binder-free electrocatalyst with superior catalytic activity and durability in HER. Thanks to its distinctive 3D microstructure featured with favourable pore-size distribution, abundant active sites provided by mini-vesicles and rapid electron transfer with the assistance of Ni foam, the as-grown grass-like CoP/NF electrocatalyst has shown a favourable overpotential in an acidic solution with an onset overpotential of ∼35 mV, an overpotential of 71 mV at a current density of 10 mA cm⁻², reduced by 60 mV in comparison with that realized by urchin-like CoP/NF nanoprickles. Moreover, it has exhibited an excellent HER activity in the alkaline medium, with an overpotential of 117 mV at 10 mA cm⁻², a Tafel slope of 63.0 mV dec⁻¹ and a long-term electrochemical durability.     

Efficient hydrogen evolution performance of phase-pure NiS electrocatalysts grown on fluorine-doped tin oxide-coated glass by facile chemical bath deposition

The production of hydrogen, the future fuel, on stable, efficient, and robust electrocatalysts represents an attractive approach for the conversion and storage of carbon-free energy resources. In this study, earth-abundant nickel sulfide (NiS) electrocatalyst were grown on fluorine-doped tin oxide (FTO) substrate by a simple and cost-effective chemical bath deposition for hydrogen evolution reaction (HER). Energy dispersive X-ray analysis and X-ray photoelectron spectra indicated the presence of highly pure NiS. The HER performance of the catalyst was examined in alkaline solution (1.0 M NaOH; pH = 13.5). Notably, NiS film prepared at 100 °C demonstrated superior HER activity with an overpotential of 290 mV to afford a current density of 10 mA/cm² and a Tafel slope of 143.4 mV/dec which are among the promising results obtained for sulfide-based HER electrocatalysts. The catalyst exhibited 100% faradaic efficiency and electrochemical stability which indicate its potential as noble-metal-free HER electrocatalyst.     

Black phosphorous dots phosphatized bio-based carbon nanofibers/bimetallic organic framework as catalysts for oxygen evolution reaction

As a multi-step and more complex half-cell reaction than the hydrogen reverse evolution reaction (HER), the oxygen evolution reaction (OER) always requires a higher overpotential than HER. In order to minimize the associated energy loss as an overpotential, these electrochemical half-reactions of water splitting should be catalyzed by suitable materials. Due to the abundant exposed surface area and extensive active edge sites, black phosphorous quantum dots (BP QDs) have shown great potential in OER. Here, BP QDs was introduced to incorporate with bio-based carbon nanofibers (CNF) and Co–Ni bimetallic organic framework (CoNiMOF), preparing a novel catalyst for oxygen evolution reaction (OER) by a facile one-pot reaction (Scheme 1). The unique structures and greater BET surface areas of CoNiMOF-BP QDs/CNF could possibly supply a larger electrocatalytic surface, expose further active sites. The obtained CoNiMOF-BP QDs/CNF possesses excellent electrocatalytic activity in alkaline electrolyte (1 M KOH) with a low overpotential of 281 mV at 10 mA cm^?2 and a low Tafel slope of 111.9 mV dec^?1. The CoNiMOF-BP QDs/CNF can remain stable for 25,000 s under alkaline electrolyte, showing excellent stability. The increase of electrocatalyst activity is mainly attributed to the synergistic effect of excellent conductivity and enriched active sites arising from BP QDs. This work not only provides an effective strategy for the development of bimetallic MOFs derived electrocatalysts, but also puts forward a new insight for the application of BP QDs in water splitting.     

Facile galvanic replacement method for porous Pd@Pt nanoparticles as an efficient HER electrocatalyst

In realm of renewable energy, development of an efficient and durable electrocatalyst for H₂ production through electrochemical hydrogen evolution reaction (HER) is indispensable. Herein, we demonstrate a simple preparation of carbon-supported nanoporous Pd with surface coated Pt (CS–PdPt) by a simple galvanic replacement reaction (GRR). The phase purity and porosity have been confirmed by XRD, HRTEM, and N₂ sorption techniques. As HER electrocatalyst, CS-PdPt showed a low overpotential of 26 mV in 0.5 M H₂SO₄ at current density of 10 mA cm⁻², which is lower than the commercial Pt/C electrode. The CS-PdPt catalyst exhibits an overpotential of 46 mV in 1 M KOH, and 50 mV in neutral buffer (1 M PBS) at 10 mA cm⁻². The CS-PdPt furnished with small Tafel values of 33, 88, and 107 mV dec⁻¹ in acidic, alkaline, and neutral medium, respectively. Accelerated durability test at 100 mV s⁻¹ for 1000 cycles demonstrated a negligible change in HER activity.     

In situ Raman spectroscopic study towards the growth and excellent HER catalysis of Ni/Ni(OH)2 heterostructure

The electrochemical water splitting to produce H₂ in high efficiency with earth-abundant-metal catalysts remains a challenge. Here, we describe a simple “cyclic voltammetry + ageing” protocol at room temperature to activate Ni electrode (AC-Ni/NF) for hydrogen evolution reaction (HER), by which Ni/Ni(OH)₂ heterostructure is formed at the surface. In situ Raman spectroscopy reveals the gradual growth of Ni/Ni(OH)₂ heterostructure during the first 30 min of the aging treatment and combined with polarization measurements, it suggests a positive relation between the Ni/Ni(OH)₂ amount and HER performance of the electrode. The obtained AC-Ni/NF catalyst, with plentiful Ni–Ni(OH)₂ interfaces, exhibits remarkable performance towards HER, with the low overpotential of only 30 mV at a H₂-evolving current density of 10 mA/cm² and 153 mV at 100 mA/cm², as well as a small Tafel slope of 46.8 mV/dec in 1 M KOH electrolyte at ambient temperature. The excellent HER performance of the AC-Ni/NF could be maintained for at least 24 h without obvious decay. Ex situ experiments and in situ electrochemical-Raman spectroscopy along with density functional theory (DFT) calculations reveal that Ni/Ni(OH)₂ heterostructure, although partially reduced, can still persist during HER catalysis and it is the Ni–Ni(OH)₂ interface reducing the energy barrier of H1 adsorption thus promoting the HER performance.     

Facile and large-scale preparation of Co/Ni-MoO2 composite as high-performance electrocatalyst for hydrogen evolution reaction

Facile fabrication of high-performance catalyst based on low-cost metals for sustainable hydrogen evolution is still a matter of cardinal significance. However, synthetic approaches for electrocatalyst are usually complicated and the yields are often low. Herein, we report a one-step simple method for the large-scale synthesis of Co/Ni-MoO₂ composite as efficient and stable hydrogen evolution reaction (HER) electrocatalyst to drive 10 mA cm^?2 current density with a low overpotential of 103 mV in basic media. Co-MoO₂ and Ni-MoO₂ were also prepared using this method with overpotential of 137 and 130 mV, respectively, to gain the same current density. These results indicate that this facile synthesis approach is of great practical importance as it can be easily used for large-scale preparation of electrocatalysts in industry.     

Boosting hydrogen evolution on NiFeZn electrocatalyst by defect surface modulation using alkali etching

Developing highly efficient catalysts using facile approaches is important for accelerating the slow reaction kinetics of the alkaline hydrogen evolution reaction (HER) and ensuring cost-effective hydrogen production. In this study, we reported a facile alkali etching method to boost the HER activity immediately after electrodeposition of a NiFeZn catalyst on Ti paper. During etching, (oxy)hydroxides were formed on the surface, and Zn species were etched from the deposits, which resulted in a roughened surface with more valleys generated between grains, facilitating a faster mass transport during the electrochemical reaction. The etched catalyst exhibited a boosted HER overpotential of 57 mV at ?10 mA/cm² and accelerated HER kinetic with Tafel slope of 97 mV/dec compared with that of the pristine catalyst. Our results demonstrated an efficient approach for boosting the catalyst activity in the alkaline HER.     

Interface engineering of crystalline/amorphous Pt/TeOx nanocapsules for efficient alkaline hydrogen evolution

Hydrogen evolution reaction (HER) is an important process in electrochemical energy technology, and efficient electrocatalysts are of great significance for renewable and sustainable energy conversion. Here, we report a facile hydrothermal and heat treatment process to synthesize a series of Pt-based nanocapsules (NCs) as an effective hydrogen evolution catalyst. The Pt/TeO_x NCs exhibit excellent HER activity in an alkaline medium. The Pt/TeO_x NCs only need the overpotential of 33 mV to achieve the current density of 10 mA cm⁻², and the Tafel slope was as low as 29 mV dec⁻¹, which was even better than that of commercial Pt/C. Detailed experimental characterizations demonstrate that the interface between the crystalline Pt/amorphous TeO_x and the strong electron transfer contribute to alkaline HER activity. This work opens up a new direction for the preparation of efficient catalysts for electrocatalytic reactions or other conversion filed.