Spatially confined growth of ultrathin NiFe layered double hydroxide nanosheets within carbon nanofibers network for highly efficient water oxidation

The rational design of catalysts with low cost, high efficient and robust stability toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, a one-pot, spatially confined strategy was reported to fabricate ultrathin NiFe layered double hydroxide (NiFe-LDH) nanosheets interconnected by ultrafine, strong carbon nanofibers (CNFs) network. The as-fabricated NiFe-LDH/CNFs catalyst exhibits enhanced OER catalytic activity in terms of low overpotential of 230 mV to obtain an OER current density of 10 mA cm^?2 and very small Tafel slope of 34 mV dec^?1, outperforming pure NiFe-LDH nanosheets assembly, commercial RuO₂, and most non-noble metal catalysts ever reported. It also delivers an excellent structural and electrocatalytic stability upon the long-term OER operation at a large current of 30 mA cm^?2 for 40 h. Furthermore, the cell assembled by using NiFe-LDH/CNFs and commercial Pt/C as anode (+) and cathode (?) ((+)NiFe-LDH/CNFs||Pt/C(?)) only requires a potential of 1.50 V to deliver the water splitting current of 10 mA cm^?2, 130 mV lower than that of (+)RuO₂||Pt/C(?) couple, demonstrating great potential for applications in cost-efficient water splitting devices.     

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.     

Transition metal carbides coupled with nitrogen-doped carbon as efficient and stable Bi-functional catalysts for oxygen reduction reaction and hydrogen evolution reaction

Developing non-precious metal catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for proton exchange membrane fuel cell (PEMFC), metal-air batteries and water splitting. Here, we report a in-situ simple approach to synthesize ultra-small sized transition metal carbides (TMCs) nanoparticles coupled with nitrogen-doped carbon hybrids (TMCs/NC, including WC/NC, V₈C₇/NC and Mo₂C/NC). The TMCs/NC exhibit excellent ORR and HER performances in acidic electrolyte as bi-functional catalysts. The potential of WC/NC at the current density of 3.0 mA cm^?2 for ORR is 0.814 V (vs. reversible hydrogen electrode (RHE)), which is very close to Pt/C (0.827 V), making it one of the best TMCs based ORR catalysts in acidic electrolyte. Besides, the TMCs/NC exhibit excellent performances toward HER, the Mo₂C/NC only need an overpotential of 80 mV to drive the current density of 10 mA cm^?2, which is very close to Pt/C (37 mV), making it the competitive alternative candidate among the reported non-precious metal HER catalysts.     

Silicon monoxide assisted synthesis of Ru modified carbon nanocomposites as high mass activity electrocatalysts for hydrogen evolution

Extremely low content of Ruthenium (Ru) nanoparticles were loaded on the carbon black (Ru/C) via reducing Ru ions with silicon monoxide. The obtained Ru/C nanocomposites exhibit an exciting electrochemical catalytic activity for hydrogen evolution reaction (HER) in the oxygen-free 0.5 M H₂SO₄ medium. The optical one (Ru/C-2) with a low Ru amount of 2.34% shows higher activity than previously reported Ru-based catalysts. The overpotential at 10 mA cm⁻² is 114 mV and the Tafel slope is 67 mV·dec⁻¹. Ru/C-2 catalyst also has good stability. The overpotential that afford the current density of 10 mA cm⁻² of 20 wt% Pt/C increased 92 mV while that of Ru/C-2 only increased 50 mV after a 30,000 s chronopotentiometry test. Furthermore, the mass activity of Ru/C-2 catalyst is even better than that of the commercial 20 wt% Pt/C when the overpotential is larger than 0.18 V. This silicon monoxide-mediated strategy may open a new way for the fabrication of high performance electrocatalysts.     

N-doped graphene quantum dots incorporated cobalt ferrite/graphitic carbon nitride ternary composite for electrochemical overall water splitting

Multicomponent electrocatalysts containing carbon supports play a crucial role in influencing the hydrogen and oxygen evolution reactions which enhance the total water splitting. Herein, we report a ternary composite with cobalt ferrite, graphitic carbon nitride, and N-doped graphene quantum dots prepared via hydrothermal technique. The purity of the samples is established by carrying out various characterization methods. The intrinsic characteristics of the obtained materials are investigated by employing electrocatalytic processes in an alkaline media toward hydrogen and oxygen evolution reactions. Cobalt ferrite/graphitic carbon nitride/N doped graphene quantum dots electrocatalyst demonstrates a very low overpotential towards hydrogen evolution reaction of 287 mV at a constant 10 mA cm^?2 current density in 1.0 M KOH. Tafel slope and R_ct values generated are 94 mV dec^?1 and 0.86 cm², respectively. Oxygen evolution reaction studies reveal an overpotential of 445 mV at 10 mA cm^?2 with a Tafel slope of 69 mV dec^?1. Finally, the cell potential needed for the cobalt ferrite/graphitic carbon nitride/N doped graphene quantum dots electrode to achieve 10 mA cm^?2 in total water splitting is only 2.0 V while displaying long-term stability.     

Physical insights into alkaline overall water splitting with NiO microflowers electrodes with ultra-low amount of Pt catalyst

Electrochemical water splitting represents a promising alternative to conventional carbon-based energy sources. The hydrogen evolution reaction (HER) is a key process, still if conducted in alkaline media, its kinetics is slow thus requiring high amount of Pt based catalysts. Extensive research has been focused on reducing Pt utilization by pursuing careful electrode investigation. Here, a low-cost chemical methodology is reported to obtain large amount of microflowers made of interconnected NiO nanowalls (20 nm thick) wisely decorated with ultralow amounts of Pt nanoparticles. These decorated microflowers, dispersed onto graphene paper by drop casting, build a high performance HER electrode exhibiting an overpotential of only 66 mV at current density of 10 mA cm^?2 under alkaline conditions. Intrinsic activity of catalyst was evaluated by measuring the Tafel plot (as low as 82 mV/dec) and turnover frequencies (2.07 s^?1 for a Pt loading of 11.2 μg cm^?2). The effect of Pt decoration has been modelled through energy band bending supported by electrochemical analyses. A full cell for alkaline electrochemical water splitting has been built, composed of Pt decorated NiO microflowers as cathode and bare NiO microflowers as anode, showing a low potential of 1.57 V to afford a current density of 10 mA cm^?2 and a good long-term stability. The reported results pave the way towards an extensive utilization of Ni based nanostructures with ultralow Pt content for efficient electrochemical water splitting.     

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.     

Enhanced activity of Pd/α-MnO2 for electrocatalytic oxygen evolution reaction

This work describes the application of α-MnO₂ and Pd/α-MnO₂ as electrocatalysts in the oxygen evolution reaction (OER). Characterization data revealed that the Pd²⁺ precursor has been oxidized during the synthesis, and the resulting Pd⁴⁺ ions have unprecedently replaced the lattice framework Mn³⁺ ions of α-MnO₂. Furthermore, formation of PdO nanoparticles was also observed. Lower OER overpotential at j = 10 mA cm^?2 (636 mV) was obtained for Pd/α-MnO₂ in relation to α-MnO₂ (700 mV), what is in alignment with the lower charge transfer resistance of Pd/α-MnO₂ (4.9 kΩ cm²) compared to α-MnO₂ (10.4 kΩ cm²). Lower Tafel slope (73 mV dec^?1) and higher TOF (2.87 × 10^?4 s^?1) at overpotential of 350 mV was obtained for Pd/α-MnO₂ in relation to α-MnO₂ (Tafel of 77 mV dec^?1 and TOF of 1.94 × 10^?4 s^?1), indicating a faster electron transfer kinetics promoted by Pd. Pd/α-MnO₂ was stable at j = 14 mA cm^?2 for 6 h.     

Platinum-rhodium alloyed dendritic nanoassemblies: An all-pH efficient and stable electrocatalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) is regarded as a feasible strategy for producing high-purity hydrogen from abundant water. It is significant yet challenging for synthesis of Pt-based pH-universal HER electrocatalysts by substantially reducing the Pt loading without any decay in the activity. Herein, bimetallic PtRh alloyed dendritic nanoassemblies (DNAs) were efficiently prepared by a facile one-pot solvothermal strategy in oleylamine (OAm), coupling with the aid of glycine and cetyltrimethylammonium chloride (CTAC). By virtue of the unique branch-like structures and compositions advantages, the PtRh DNAs catalyst showed steeply enhanced HER activity with small overpotentials (i.e. 28 mV in 1.0 M KOH, 23 mV in 1.0 M phosphate buffer solution and 27 mV in 0.5 M H₂SO₄) at the current density of 10 mA cm⁻², surpassing those of commercial Pt/C under such conditions. This work provides a facile and rational strategy to construct advanced Pt-based bimetallic electrocatalyst for energy-correlated applications.     

Low Ir-content Ir/Fe@NCNT bifunctional catalyst for efficient water splitting

In order to reduce the cost of electrocatalysts and increase the exposure of the Ir active sites while ensuring the stability of the catalyst, a N-doped carbon nanotube (NCNT) is applied as a conductive support to confine the Ir clusters for avoiding them growing up via a modified method based on pyrolysis of a mixture of melamine, ferric chloride and iridium trichloride. It is found that Ir species in the as-obtained Ir(20)/Fe@NCNT-900 composite exist in two forms, Ir nanoclusters (1–2 nm) dotted on the wall of NCNT and the Ir atomically scattered on the Fe nanoparticles wrapped in the NCNT. Although the Ir content of Ir(20)/Fe@NCNT-900 is extremely low (～4 wt% Ir), the composite catalyst delivers excellent activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with an exceptionally low overpotential of 4.7 mV/11 mV for HER and 300 mV/270 mV for OER to drive 10 mA cm^?2 in 0.5 M H₂SO₄/1.0 M KOH electrolyte respectively, which exceeds the commercial Pt/C (20 wt% Pt) and IrO₂ benchmarks. In addition, it has much higher mass activity for OER at 1.55 V (1.78 A mg^?1_Ir) than those of the referenced catalysts in acid. The cell voltage of the two-electrode system assembled by Ir(20)/Fe@NCNT-900 for total water splitting in acidic and alkaline media are only 1.520 V and 1.510 V to afford 10 mA cm^?2 separately, lower than that of Pt/C||IrO₂ and with a good stability. Our work provides a construction method of low-content precious metal composite catalysts which can be applied in OER and overall water splitting field.     

Surfactant-assisted synthesis of platinum nanoparticle catalysts for proton exchange membrane fuel cells

High-performance platinum nanoparticle catalysts (Pt–NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mg_Pt^?1 and specific activity (SA) of 0.077 mA cm^?2, higher than those of commercial Pt/C (0.023 A mg_Pt^?1 and 0.035 mA cm^?2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm^?2, which is about 1.24 times larger than that of commercial Pt/C.     

Facile construction of 3D hyperbranched PtRh nanoassemblies: A bifunctional electrocatalyst for hydrogen evolution and polyhydric alcohol oxidation reactions

Development of highly effective and stable electrocatalysts is urgent for various energy conversion applications. Herein, a facile co-reduction approach was developed to fabricate three-dimensional (3D) hyperbranched PtRh nanoassemblies (NAs) under solvothermal conditions, where creatinine and cetyltrimethylammonium chloride (CTAC) were employed as the structure-directing agents. The as-synthesized nanocatalyst exhibited intriguing catalytic characters for hydrogen evolution reduction (HER) with a low overpotential (20 mV) at 10 mA cm⁻² and a small Tafel slope (49.01 mV dec⁻¹). Meanwhile, the catalyst showed remarkably enlarged mass activity (MA: 2.16/2.02 A mg⁻¹) and specific activity (SA: 4.16/3.88 mA cm⁻²) towards ethylene glycol and glycerol oxidation reactions (EGOR and GOR) alternative to commercial Pt black and homemade Pt₃Rh nanodendrites (NDs), PtRh₃ NDs and Pt nanoparticles (NPs). This method offers a feasible platform to fabricate bifunctional, efficient, durable and cost-effective nanocatalysts with finely engineered structures and morphologies for renewable energy devices.     

Atomic interface engineering: Strawberry-like RuO2/C hybrids for efficient hydrogen evolution from ammonia borane and water

Efficient hydrogen production plays a key role in establishing hydrogen economy in the current world. In this study, we fabricated ultrafine RuO₂ nanoparticles on carbon black to form a strawberry-like RuO₂/C hybrid, using by a solid-phase grinding and subsequent low-temperature annealing. The synthesized hybrid displays very low reaction activation energy (28.5 KJ mol^?1) for hydrogen evolution from ammonia borane. In case of hydrogen evolution from alkaline water, it also exhibits a remarkably improved electrocatalytic activity than a commercial Pt/C, with an ultra-low overpotential of 8 mV (at 10 mA cm^?2). For the above bifunctional catalyst, the formed C–Ru–C bonds between the ruthenium oxide and carbon result in the ultrahigh activity of the hybrid, as evidenced by DFT results. This work offers a guideline to synthesize efficient metal-based (Ru, Pd, Rh, Ir, Au, etc.) catalysts with smart structures for catalysis.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

Metal-organic frameworks derived self-supported Ni2P nanorod arrays for electrocatalytic hydrogen evolution

The development of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is of importance. Herein, we demonstrate a self-supported Ni₂P nanostructure with nanorod arrays morphology, fabricated by directly growing metal-organic frameworks (MOFs) on the commercial nickel foam prior to phosphorization treatment, as an electrocatalyst for HER. This electrocatalyst exhibits remarkable electrocatalytic HER activity in an alkaline electrolyte, affording current densities of 10 and 100 mA cm^?2 at the overpotentials of 120 and 168 mV, respectively, accompanied with a low Tafel slope of 37 mV dec^?1. Furthermore, this electrocatalyst shows a current density of 105 mA cm^?2, and this current density can be retained for more than 20 h, suggesting its superior stability. This remarkable HER performance is believed a result of superiority for its structural integrality and mechanical stability.     

ZIF67@MoO3 NSs@NF composite electrocatalysts reinforced by chemical bonds and oxygen vacancy for efficient oxygen evolution reaction and overall water-splitting

A kind of composite electrocatalysts with the structure of MoO₃ nanosheets coated by ZIF67 nanocrystals and grown on the nickel foam substrate (ZIF67@MoO₃ NSs@NF) is prepared and mainly used as the electrode for oxygen evolution reaction (OER) and overall water splitting. The excellent electrocatalytic activity of ZIF67@MoO₃ NSs@NF are demonstrated. It can use the overpotential (?) of 178 mV and 386 mV respectively to drive 10 mA cm^?2 and 50 mA cm^?2. It is also observed that the ZIF67@MoO₃ NSs@NF electrode has the highest initial current density (45.7 mA cm^?2) at 1.618 V and can maintain more than 90% of the initial current density after 20,000 s. The ZIF67@MoO₃ NSs@NF electrode also shows the small HER overpotential of 135 mV at 10 mA cm^?2. Furthermore, the voltage of ZIF67@MoO₃ NSs@NF as a bifunctional overall water splitting catalysts is 1.58 V at 10 mA cm^?2, which is superior to another noble metal electric catalyst combination RuO₂/NF(+)//Pt–C/NF(?). And the ZIF67@MoO₃ NSs@NF(+)//ZIF67@MoO₃ NSs@NF(?) combination can maintain more than 90% of the initial current density after 65,000 s at 1.58 V. The main reason is the composite interface of MoO₃ NSs and ZIF67 phases with Co–O bonds, C–O–Mo bonds and oxygen vacancies defects facilitates the increase of the active sites and efficient electron transfer rate.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

Facile construction of porous and heterostructured molybdenum nitride/carbide nanobelt arrays for large current hydrogen evolution reaction

The development of cost-effective, highly efficient and stable electrocatalysts for alkaline water electrolysis at a large current density has attracted considerable attention. Herein, we reported a one-dimensional (1D) porous Mo₂C/Mo₂N heterostructured electrocatalyst on carbon cloth as robust electrode for large current hydrogen evolution reaction (HER). The MoO₃ nanobelt arrays and urea were used as the metal and non-metal sources to fabricate the electrocatalyst by one-step thermal reaction. Due to the in-situ formed abundant high active interfaces and porous structure, the Mo₂C/Mo₂N electrocatalyst shows enhanced HER activity and kinetics, as exemplified by low overpotentials of 54, 73, and 96 mV at a current density of 10 mA cm^?2 and small Tafel slopes of 48, 59 and 60 mV dec^?1 in alkaline, neutral and acid media, respectively. Furthermore, the optimal Mo₂C/Mo₂N catalyst only requires a low overpotential of 290 mV to reach a large current density of 500 mA cm^?2 in alkaline media, which is superior to commercial Pt/C catalyst (368 mV) and better than those of recently reported Mo-based electrocatalysts. This work paves a facile strategy to construct highly efficient and low-cost electrocatalyst for water splitting, which could be extended to fabricate other heterostructured electrocatalyst for electrocatalysis and energy conversion.     

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.     

Adjusting electronic structure coupling of Fe–Ni2P (NiFeP-MOF) multilevel structure for ultra-activity and durable catalytic water oxidation

Efficient electrocatalyst for alkaline oxygen evolution reaction is the critical core to the wide application of metal-air energy storage and water electrolysis hydrogen energy. Therefore, appropriate design of highly active and stable non-noble metal oxygen evolution electrocatalyst with good electronic structure and multilevel structure is both a goal and a challenge. Here, we report a Fe–Ni₂P electrocatalyst (NiFeP-MOF) with multilevel structure, which was obtained by anion exchange on the basis of Fe–Ni(OH)₂ (NiFe-MOF) grown on nickel foam in situ by solvothermal method. As expected, Fe substitution regulates the Ni oxidation state in the NiFeP-MOF and realizes electronic structure coupling, showing a highly active and stable oxygen evolution reaction (OER) in alkaline electrolyte solution. Specifically, the NiFeP-MOF demonstrates an ultralow overpotentials (232 mV, 10 mA cm^?2; 267 mV 100 mA cm^?2), respectively, an extremely small Tafel slope (34 mV dec^?1). Separately, the electrocatalyst shows an excellent cycle stability at 10 mA cm^?2 for 12 h (43,200 s). More importantly, this work come up with an available policy for the preparation of excellent alkaline hydrolysis electrolysis catalysts and air cathodes with excellent performance.