Carbonized Wood Decorated with Ternary Heterogeneous MoS2-MoP-Mo2C Nanoparticles for pH-Universal Hydrogen Evolution

The assembly of diverse active materials significantly enhances the efficiency of the electrocatalytic hydrogen evolution reaction (HER). Herein, we prepare a three-phase composite structure electrocatalyst on carbonized wood, in which molybdenum carbide and molybdenum phosphide are attached to molybdenum sulfide nanosheets (MoS2-MoP-Mo2C@CW) through the hydrothermal method in combination with high-temperature calcination for a pH-universal HER. MoS2 possesses abundant unsaturated coordination edge active sites, thus facilitating the adsorption and desorption of the hydrogen intermediate (H*). The synergistic effect between MoS2, MoP featuring favorable electronic conductivity, and Mo2C holding strong adsorption of H* enhances the catalytic activity for the pH-universal HER. Moreover, the carbonized wood with a hierarchical porous structure and aligned microchannels accelerates mass transport during the HER. As a result, the molybdenum-based self-supported composite electrode exhibits outstanding HER performance with the low overpotentials of 46, 84, and 65 mV to achieve the current density of 10 mA cm-2 and the corresponding Tafel slopes of 57, 111 mV, and 63 mV dec-1 in alkaline, neutral, and acidic environments, respectively. MoS2-MoP-Mo2C@CW also shows a long-term durability of 200 h over a broad pH range at 10 mA cm-2. This work provides an effective strategy for the development of multiphase carbonized wood-based electrocatalysts for the pH-universal HER.

Free-Electron Inversive Modulation to Charge Antibonding Orbital of ReS2 Cocatalyst for Efficient Photocatalytic Hydrogen Generation

The free electron transfer between cocatalyst and photocatalyst has a great effect on the bonding strength between the active site and adsorbed hydrogen atom (Hads ), but there is still a lack of effective means to purposely manipulate the electron transfer in a beneficial direction of H adsorption/desorption activity. Herein, when ReSx cocatalyst is loaded on TiO2 surface, a spontaneous free-electron transfer from ReSx to TiO2 happens due to the smaller work function of ReSx , causing an over-strong S-Hads bond. To prevent the over-strong S-Hads bonds of ReSx in the ReSx /TiO2 , a free-electron reversal transfer strategy is developed to weaken the strong S-Hads bonds via increasing the work function of ReSx by incorporating O to produce ReOSx cocatalyst. Research results attest that a larger work function of ReOSx than that of TiO2 can induce reversal transfer of electrons from TiO2 to ReOSx to produce electron-rich S(2+δ)- , causing the increased antibonding-orbital occupancy of S-Hads in ReOSx /TiO2 . Accordingly, the stability of adsorbed H on S sites is availably decreased, thus weakening the S-Hads of ReOSx . In this case, an electron-rich S(2+δ)- -mediated "capture-hybridization-conversion" mechanism is raised . Benefiting from such property, the resultant ReOSx /TiO2 photocatalyst exhibits a superior H2 -evolution rate of 7168 µmol h-1 g-1 .

Orbital Modulation with P Doping Improves Acid and Alkaline Hydrogen Evolution Reaction of MoS2

There has been great interest in developing and designing economical, stable and highly active electrocatalysts for the hydrogen evolution reaction (HER) via water splitting in an aqueous solution at different pH values. Transition-metal dichalcogenides (TMDCs), e.g., MoS₂, are identified to be promising catalysts for the HER due to the limited active sites at their edges, while the large basal plane of MoS₂ is inert and shows poor performance in electrocatalytic hydrogen production. We theoretically propose orbital modulation to improve the HER performance of the basal plane of MoS₂ through non-metal P doping. The substitutional doping of P provides empty 3p_z orbitals, perpendicular to the basal plane, can enhance the hydrogen adsorption for acid HER and can promote water dissociation for alkaline HER, which creates significant active sites and enhances the electronic conductivity as well. In addition, 3P-doped MoS₂ exhibits excellent HER catalytic activity with ideal free energy at acid media and low reaction-barrier energy in alkaline media. Thus, the doping of P could significantly boost the HER activity of MoS₂ in such conditions. Our study suggests an effective strategy to tune HER catalytic activity of MoS₂ through orbital engineering, which should also be feasible for other TMDC-based electrocatalysts.

Electronic modulation of Co2P nanoneedle arrays by the doping of transition metal Cr atoms for a urea oxidation reaction

Urea electrolysis is of great interest for energy-related applications, but it is limited by a complex six-electron transfer process with slow kinetics. Herein, the in situ growth of Cr-doped Co₂P homogeneous nanoneedle arrays on nickel foam substrates (Cr-Co₂P/NF) was reported for the first time by a typical hydrothermal and low-temperature phosphorization process. The appropriate amount of Cr doping was found to promote the electronic modulation of active centers and the expansion of the specific active surface area, resulting in the superior performance of the urea oxidation reaction (UOR). It is noteworthy that Cr_0.4-Co₂P/NF exhibited a superior performance of the UOR at an onset potential of 1.290 V and a cell voltage of 1.333 V at 50 mA cm^-2 in 1 M KOH containing 0.5 M urea, which is one of the best catalytic activities reported so far. The experimental results demonstrate that the enhanced catalytic activity can be attributed to favorable electronic regulation, an improved charge transfer rate and increased exposure to active sites. Density functional theory (DFT) calculation indicates that the appropriate doping of Cr effectively regulates and controls the adsorption energy of urea and the conductivity of the Co₂P material itself. This work provides new ideas for the development of robust catalysts for the electrolysis of urea through doping strategies.

Defects engineering on CrOOH by Ni doping for boosting electrochemical oxygen evolution reaction

The design and construction of active centres are key to exploring advanced electrocatalysts for oxygen evolution reaction (OER). In this work, we demonstrate thein situconstruction of point defects on CrOOH by Ni doping (Ni-CrOOH/NF). Compared with pure CrOOH/NF, Ni-CrOOH/NF showed enhanced OER activity. The effect of the amount of Ni introduced on the OER performance was investigated. Ni_0.2-CrOOH/NF, the best introduction of Ni, uses a low overpotential of 253 mV to achieve a current density of 10 mA cm^-2with a high turnover frequency of 0.27 s^-1in 1.0 M NaOH. In addition, the electrocatalytic performance of Ni_0.2-CrOOH/NF showed little deterioration after 1000-cycle cyclic voltammetry scanning. In the potentiostatic test, activity was stable for at least 20 h.

Investigation of the supercapacitor behavior of MoS2 and Fe-doped MoS2 nano-flowers synthesized using the hydrothermal method

Flower-like nanosheets of Fe-doped MoS2 with high porosity exhibit better electrochemical activities in supercapacitors.

A facile photochemical strategy for the synthesis of high-performance amorphous MoS2 nanoparticles

It is difficult to avoid the formation of polysulfides by traditional chemical methods, and the synthesis of high purity amorphous MoS₂ nanomaterials under ambient conditions is still a challenging task. Here we present a new and facile photochemical strategy for the synthesis of amorphous MoS₂ nanomaterials, which is achieved by irradiating a mixed solution containing ammonium molybdate, formic acid and sodium sulfide simply with a Xe lamp for 3 min. The mechanism study reveals that the key step in this synthesis is the photolysis of formic acid to produce free radicals which can rapidly reduce Mo⁶⁺ to Mo⁴⁺, which then combines with S^2- to form MoS₂ and inhibits the formation of S-S^2- by preventing S^2- from participating in the reduction reaction. In addition, the results of a series of experiments indicate that the as-prepared amorphous MoS₂ features a small particle size, uniform morphology and relatively large specific surface area, and shows excellent performance in the removal of inorganic heavy metal ions (mercury, lead and cadmium ions) and organic pollutants (rhodamine B and tetracycline), catalase catalysis and a lithium battery anode, showing its great potential and broad application prospects in the fields of environmental remediation, clean energy and green catalysis.

In situsynthesis of Fe-doped CrOOH nanosheets for efficient electrocatalytic water oxidation

The oxygen evolution reaction (OER) is a process in electrochemical water splitting with sluggish kinetics that needs efficient non-noble-metal electrocatalysts. There have been few studies of CrOOH electrocatalysts for water oxidation due to their low performance. Herein,in situsynthesized Fe-doped CrOOH nanosheets on Ni foam (Fe-CrOOH/NF) were designed as electrocatalysts and performance in the OER was obviously improved. The effect of the amount of Fe doping was also investigated. Experiments revealed that the best performance of Fe-CrOOH/NF requires low overpotentials of 259 mV to reach 20 mA cm^-2together with a turnover frequency of 0.245 s^-1in 1.0 M KOH, which may suggest a new direction for the development of Fe-doped OER electrocatalysts.

Controlled Synthesis of V-Doped Heterogeneous Ni3S2/NiS Nanorod Arrays as Efficient Hydrogen Evolution Electrocatalysts

The development of low-cost and high-efficient electrocatalysts toward hydrogen evolution reaction (HER) is highly desirable and challenging. Herein, the novel V-doped Ni₃S₂/NiS heterostructure nanorod arrays grown on nickel foam (VNS/NF-WM) are synthesized via a facile methanol-assisted hydrothermal method. We demonstrate that the morphology, phase composition, and crystallinity of VNS/NF are well modulated by tuning the ratios of water/methanol solvent. The optimized VNS/NF-WM-heterostructured nanorod (volume ratio of water/methanol is 3:1) exhibits superior HER electrocatalytic activity with low overpotentials of 85 and 218 mV to yield current density values of 10 and 100 mA cm^-2, respectively, meanwhile sustaining an excellent stability with almost an unchanged current density of 10 mA cm^-2 for 60 h. Our work offers fresh insights into the rational design of highly active and stable earth-abundant-heterostructured electrocatalysts for the hydrogen fuel production.

A Ni-MOF nanosheet array for efficient oxygen evolution electrocatalysis in alkaline media

Ni-MOF(bpdc) nanosheet array on nickel foam (Ni-MOF/NF) is a superior OER catalyst with a requirement of an overpotential of 350 mV to attain 20 mA cm⁻² in 1.0 M KOH.

A hierarchical CuO@NiCo layered double hydroxide core–shell nanoarray as an efficient electrocatalyst for the oxygen evolution reaction

A hierarchical CuO@NiCo LDH core–shell nanoarray on copper foil (CuO@NiCo LDH/CF) acts as an efficient and durable oxygen-evolving electrocatalyst, capable of driving 20 mA cm⁻² at an overpotential of only 256 mV in 1.0 M KOH.

A NiCo LDH nanosheet array on graphite felt: an efficient 3D electrocatalyst for the oxygen evolution reaction in alkaline media

A NiCo LDH nanosheet array on graphite felt is an efficient 3D OER catalyst with the need for an overpotential of 249 mV to drive 20 mA cm⁻² in 1.0 M KOH.

Coupling 0D and 1D Carbons for Electrochemical Hydrogen Production Promoted by a Percolation Mechanism

Developing hydrogen evolution reaction (HER) electrocatalysts with high activity, durability and moderate price is essential for sustainable hydrogen energy utilization. Here, the facile coupling of carbon dots (CDs, 0D carbon materials) and carbon fibres (CFs, 1D carbon materials) for enhanced electrochemical hydrogen production was demonstrated. Electrochemical tests revealed that the CD/CF catalysts showed outstanding catalytic activity with a small overpotential of 280 mV at the current density of 10 mA cm^-2 , a small Tafel slope of 87 mV dec^-1 and prominent durability. Percolation theory was for the first time introduced to interpret the catalytic mechanism of the CD/CF catalysts. The special morphology assembled by the 0D carbons constituted the percolating clusters and promoted electron transport throughout the 1D carbons. The strategy and theory can be adapted to general electrocatalytic applications for achieving and interpreting precise tuning on highly efficient electron transfer in electrocatalysts.

Nanostructured Ni2SeS on Porous-Carbon Skeletons as Highly Efficient Electrocatalyst for Hydrogen Evolution in Acidic Medium

Nickel dichalcogenides have received extensive attention as promising noble-metal-free nanocatalysts for a hydrogen evolution reaction. Nonetheless, their catalytic performance is restricted by the sluggish reaction kinetics, limited exposed active sites, and poor conductivity. In this work, we report on an effective strategy to solve those problems by using an as-designed new porous-C/Ni₂SeS nanocatalyst with the Ni₂SeS nanostubs anchored on with porous-carbon skeletons process. On the basis of three advantages, as the enhancement of the intrinsic activity using the ternary sulfoselenide, increased number of exposed active sites due to the 3D hollow substrate, and increased conductivity caused by porous-carbon skeletons, the resulting porous-C/Ni₂SeS requires an overpotential of only 121 mV at a current density of 10 mA cm^-2 with a Tafel slope of 78 mV dec^-1 for hydrogen evolution in acidic media and a good long-term stability. Density functional theory calculations also show that the Gibbs free energy of hydrogen adsorption of the Ni₂SeS was -0.23 eV, which not only is close to the ideal value (0 eV) and Pt reference (-0.09 eV) but also is lower than those of NiS₂ and NiSe₂; large electrical states exist in the vicinity of the Fermi level, which further improves its electrocatalytic performance. This work provides new insights into the rational design of ternary dichalcogenides and hollow structure materials for practical applications in HER catalysis and energy fields.

Engineering interfacial structures to accelerate hydrogen evolution efficiency of MoS2 over a wide pH range

Developing low-cost electrocatalysts with outstanding electrochemical performance for water splitting over a wide pH range is urgently desired to meet the practical needs in different areas. Herein, a highly efficient hierarchical flower-like CoS₂@MoS₂ core-shell nanostructured electrocatalyst is fabricated by a two-step strategy, in which MoS₂ nanosheets with a layered structure are grown on the CoS₂ core supported on carbon paper (CP) and used as hydrogen evolution reaction (HER) electrocatalysts working in the whole pH range (0-14). Remarkably, benefiting from the interface-engineering in this 3D core-shell structure of the electrocatalyst, the optimum CoS₂@MoS₂/CP catalyst exhibits outstanding HER activity over a wide range of pH values and an overpotential of 69 mV in acidic solution, 145 mV in neutral solution and 82 mV in alkaline solution, respectively, to afford the standard current density of 10 mA cm^-2. Furthermore, it demonstrates superior stability under different pH conditions for at least 48 h. Density functional theory (DFT) calculations are performed to gain further insight into the effect of CoS₂@MoS₂ interfaces, revealing that the strong interfacial interaction between CoS₂ and MoS₂ dramatically reduces the Gibbs free energy of hydrogen adsorption and the energy barrier for water dissociation, thus enhancing the electrochemical HER activity in the whole pH range (0-14).

Hierarchical CuO@ZnCo LDH heterostructured nanowire arrays toward enhanced water oxidation electrocatalysis

It is of great importance to design and develop complex heterostructured nanocatalysts with superior electrochemical performance to that of single structured ones. Here, we report the hydrothermal fabrication of a hierarchical heterostructured CuO@ZnCo layered double hydroxide nanowire array on a copper foil (CuO@ZnCo LDH/CF). As a self-supported electrocatalyst for water oxidation, CuO@ZnCo LDH/CF has superior catalytic activity with the requirement of a low overpotential of 270 mV to attain 10 mA cm-2 in 1.0 M KOH. In addition, it shows strong durability to maintain its activity for at least 24 h.

Facile synthesis of amorphous MoSx–Fe anchored on Zr-MOFs towards efficient and stable electrocatalytic hydrogen evolution

MoS_x–Fe nanoparticles dispersively, firmly anchored on a UiO-66-(OH)₂ support via phenol–Fe(iii) coordination exhibit superior electrocatalytic hydrogen evolution performance in an acidic electrolyte.

Mo2C-embedded biomass-derived honeycomb-like nitrogen-doped carbon nanosheet/graphene aerogel films for highly efficient electrocatalytic hydrogen evolution

Honeycomb-like Mo₂C@nitrogen-doped carbon nanosheet/graphene aerogel films were synthesized successfully by solid-state reaction between (NH₄)₆Mo₇O₂₄ and regenerated chitin/graphene oxide aerogel.

Hydrothermal synthesis of polydopamine-functionalized cobalt-doped lanthanum nickelate perovskite nanorods for efficient water oxidation in alkaline solution

Perovskite oxides have attracted great attention recently for their low cost and high intrinsic activity in the electrochemical oxygen evolution reaction (OER). In this work, we synthesized highly efficient OER electrocatalysts in alkaline solution by carbonization of polydopamine (PDA)-functionalized cobalt-doped lanthanum nickelate perovskite nanorod (La₅Ni₃Co₂) complexes. The calcination temperature and molar ratio for La, Ni, and Co were optimized. The as-prepared complex with a molar ratio of 5 : 3 : 2 (La : Ni : Co) and a calcination temperature of 500 °C displayed enhanced OER activity and excellent durability. In 1.0 M KOH, the overpotential of the as-prepared catalyst at a current density of 10 mA cm^-2 was 0.360 V, which is comparable to those of noble metal-based materials or perovskite-based materials. The Tafel slope is 48.1 mV dec^-1, which is smaller than those of prepared composites. The satisfactory oxygen evolution activity could be attributed to the increased Co₃O₄, O₂^2-/O^-, pyridine N, and quaternary N species after calcination treatment, and the improved amount of Ni³⁺ during the OER process, as well as the high surface area and electrochemical surface area.

Cu3N nanowire array as a high-efficiency and durable electrocatalyst for oxygen evolution reaction

Developing non-precious oxygen evolution reaction (OER) electrocatalysts with high performance and long-term stability has drawn considerable research interest in recent years. In this communication, we report a self-supported Cu3N nanowire array on copper foam (Cu3N NA/CF) which is derived from a Cu(OH)2 nanowire array on copper foam (Cu(OH)2 NA/CF) through a nitridation process. Intriguingly, this 3D electrode exhibits marvellous OER activity with the need of an overpotential of only 298 mV at a current density of 20 mA cm-2 in 1.0 M KOH. In addition, the obtained electrocatalyst is capable of maintaining its high performance for at least 25 h under a static current density of 20 mA cm-2.

High-performance N2-to-NH3 fixation by a metal-free electrocatalyst

The Haber-Bosch process for the synthesis of ammonia (NH3) not only causes large energy consumption but also leads to CO2 emissions. Electrocatalytic hydrogenation of N2 to NH3 under ambient conditions is a highly desirable alternative method; however, it needs an efficient electrocatalyst. In this study, we report a mesoporous boron nitride (MBN) metal-free electrocatalyst for the N2 reduction reaction under ambient conditions. Owing to its mesoporous structure, this MBN electrocatalyst can expose more active sites, resulting in an outstanding NH3 formation rate of 18.2 μg h-1 mgcat.-1 with a faradaic efficiency of 5.5% at -0.7 V vs. reversible hydrogen electrode in 0.1 M Na2SO4. It also demonstrates strong long-term electrochemical durability.

Cobalt-Tannin-Framework-Derived Amorphous Co-P/Co-N-C on N, P Co-Doped Porous Carbon with Abundant Active Moieties for Efficient Oxygen Reactions and Water Splitting

It remains a tremendous challenge to develop a low-cost, earth-abundant, and efficient catalyst with multifunctional activities for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Herein, a facile and scalable avenue was developed to prepare amorphous Co-P/Co-N-C supported on N, P co-doped porous carbon (Co-P/Co-N-C/NPC) with a large specific surface area (1462.9 m²  g^-1 ) and abundant reactive sites including Co-P, Co-N and NPC. The prepared electrocatalyst exhibits outstanding catalytic performance for HER (η=234 mV at 10 mA cm^-2 ), OER (η=374 mV at 10 mA cm^-2 ), and ORR (E_1/2 =0.89 V, vs. reversible hydrogen electrode). Benefiting from the excellent HER performance and outstanding OER activity, the Co-P/Co-N-C/NPC delivers a current density of 10 mA cm^-2 for overall water splitting at a cell voltage of 1.59 V, which is comparable with the IrO₂ -Pt/C couple electrode.

A hierarchically-assembled Fe–MoS2/Ni3S2/nickel foam electrocatalyst for efficient water splitting

Hierarchically-assembled Fe–MoS₂/Ni₃S₂/NF demonstrates excellent HER, OER and full water splitting catalytic performances in an alkaline electrolyte.

Amorphous Ni–Fe double hydroxide hollow nanocubes enriched with oxygen vacancies as efficient electrocatalytic water oxidation catalysts

A hollow nanocube Ni_0.75Fe_0.25(OH)_x exhibits good oxygen evolution activity, which should be attributed to electronic modulation and abundant oxygen vacancies.

Hierarchical Cobalt Borate/MXenes Hybrid with Extraordinary Electrocatalytic Performance in Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is a key reaction for many renewable energy storage and conversion techniques. Developing efficient non-precious metal-based electrocatalysts for OER has attracted increasing attention. Herein is reported a strategy to fabricate hierarchical cobalt borate/Ti₃ C₂ T_x MXene (Co-B_i /Ti₃ C₂ T_x ) hybrid through fast chemical reactions at room temperature. This interesting hierarchical structure of Co-B_i /Ti₃ C₂ T_x hybrid is beneficial for exposing more active sites, improving mass diffusion, and charge-transfer pathways for electrochemical reaction. Moreover, a strong interaction between Co-B_i and Ti₃ C₂ T_x ensures efficient charge transfer and facilitates the electrostatic attraction of more anionic intermediates for a fast redox process. Consequently, the hierarchical Co-B_i /Ti₃ C₂ T_x hybrid shows extraordinary OER catalytic activity to deliver a current density of 10 mA cm^-2 at an overpotential of 250 mV, and a Tafel slope of about 53 mV dec^-1 .

Highly stable photoelectrochemical cells for hydrogen production using a SnO2-TiO2/quantum dot heterostructured photoanode

Photoelectrochemical (PEC) water splitting implementing colloidal quantum dots (QDs) as sensitizers is a promising approach for hydrogen (H2) generation, due to the QD's size-tunable optical properties. However, the challenge of long-term stability of the QDs is still unresolved. Here, we introduce a highly stable QD-based PEC device for H2 generation using a photoanode based on a SnO2-TiO2 heterostructure, sensitized by CdSe/CdS core/thick-shell "giant" QDs. This hybrid photoanode architecture leads to an appreciable saturated photocurrent density of ∼4.7 mA cm-2, retaining an unprecedented ∼96% of its initial current density after two hours, and sustaining ∼93% after five hours of continuous irradiation under an AM 1.5G (100 mW cm-2) simulated solar spectrum. Transient photoluminescence (PL) measurements demonstrate that the heterostructured SnO2-TiO2 photoanode exhibits faster electron transfer compared with the bare TiO2 photoanode. The lower electron transfer rate in the TiO2 photoanode can be attributed to slow electron kinetics in the ultraviolet regime, revealed by ultrafast transient absorption spectroscopy. Graphene microplatelets were further introduced into the heterostructured photoanode, which boosted the photocurrent density to ∼5.6 mA cm-2. Our results demonstrate that the SnO2-TiO2 heterostructured photoanode holds significant potential for developing highly stable PEC cells.