Search

Developing new forms of flexible zinc–air (Zn–air) batteries is crucial to economic growth. Nevertheless, the absence of an oxygen evolution reaction catalyst with high catalytic efficiency and low-cost causes instability of Zn–air battery cycling and economic unviability, respectively. In this paper, a leaf-like N-doped carbon structure with CoS2 nanoparticles self-supported on carbon fiber paper (CoS2-CZ@CFP) was developed as an air electrode for Zn–air batteries, which not only uses nonprecious metal elements, but also has a self-supporting configuration, enhancing the contact between the catalyst and electrode while facilitating the transfer of electrons. Sulfur as the source gas was introduced into Co-doped metal–organic skeletons (Co-ZIFs) anchored on carbon fiber paper (CFP) for in situ vulcanizing transition metal Co, which successfully ensures the uniform distribution of sulfide particles in the carbon matrix, hence enriching active catalyst sites. The CoS2-CZ@CFP demonstrated an overpotential of 1.611 V at J = 50 mA cm−2, superior to RuO2@CFP (1.814 V). A Zn–air battery fabricated using the synthesized CoS2-CZ@CFP exhibited an extended life cycle of 117 h. This research paves the way for a novel method of designing self-supporting configurations of sulfides and carbon matrix composites as promising air electrodes applicable to Zn–air batteries. [ABSTRACT FROM AUTHOR]

In this paper, a novel Pt/CoP/C photo-electro synergistic catalyst was successfully synthesized by a hydrothermal method combined with phosphorus doping treatment. The addition of Vulcan XC-72R is in favor of effectively preventing agglomeration of active catalytic sites, resulting in more uniform and smaller Pt and CoP nanoparticles. The as-obtained Pt/CoP/C shows excellent photo-electro catalytic performance for the HER with simulated solar light irradiation. The optimal hydrogen production is 5384.18 mmol h−1 g−1, which is obviously higher than that of the commercial catalyst (20 wt% Pt/C: 4608.52 mmol h−1 g−1). The research results show that introducing cobalt phosphide into the Pt catalyst can improve the electrocatalytic activity and stability for the HER; in particular, the existence of Co3O4 in Pt/CoP/C leads to an efficient photo-electro catalysis under irradiation, which significantly improves the catalytic activity of Pt. The results above provide a novel strategy for the rational design of cost-effective Pt-based composites towards a fast HER. [ABSTRACT FROM AUTHOR]

Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo2N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo2N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo2N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (‖ΔGH*‖), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo2N to form stable structures of Co doped Mo2N (Co–Mo2N) and Cu doped Mo2N (Cu–Mo2N). Compared with pristine Mo2N, both Cu–Mo2N and Co–Mo2N demonstrated a much improved cocatalytic effect over g-C3N4 in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co–Mo2N with the highest conductivity and lowest ‖ΔGH*‖ illustrated the best cocatalytic effect, and the H2 production performance (367.8 μmol g−1 h−1) of Co–Mo2N/g-C3N4 achieved was 10 and 5 times higher than those of Mo2N/g-C3N4 and Cu–Mo2N/g-C3N4. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application. [ABSTRACT FROM AUTHOR]

Element doping and construction of heterojunction composites are the most common ways to enhance g-C3N4, which are very attractive in achieving high photocatalytic activity. In this study, 2D nanosheet structured BCN was obtained by doping B atoms with graphite carbon nitride. Subsequently, Ti MOFs were loaded on BCN to obtain a Z-scheme heterojunction composite TBCN through calcination. Under simulated sunlight, the photocatalytic hydrogen production rate of the TBCN heterostructure was 1242 μmol h−1 g−1, which was 2.2 times higher than that of BCN and 9.34 times higher than that of bulk graphite carbon nitride (GCN). Experimental results showed that the construction of a Z-scheme heterojunction composite (TBCN) could effectively adjust the material band gap position, expand the light absorption range, enhance electron transfer and inhibit electron–hole recombination, which are crucial for efficient photocatalysis. This study not only provides a strategy for constructing heterojunction composites in the field of g-C3N4 photocatalytic hydrogen evolution, but also deeply analyzes the electron migration direction and the reasons for enhancing carrier separation in the Z-type heterojunction scheme, thus providing potential guidance for future research. [ABSTRACT FROM AUTHOR]

Electrocatalysts for hydrogen production play a crucial role in advancing the green economy. However, the sluggish kinetics of the hydrogen evolution reaction (HER) limited its application. Therefore, efficient strategies with a tailored d-band center adjustment are highly desirable. In this study, we synthesized N, P-doped carbon matrix-confined Mo-doped FeP nanoparticles using a simple strategy to optimize the catalyst's d-band center. Mo-FeP@NPC presents an excellent HER performance of 63 mV (H2SO4) and 116 mV (KOH) at −10 mA cm−2 in acid and alkaline electrolytes, separately. Theoretical calculations confirm that the outstanding HER performance originates from the strong electronic coupling between atoms, thus upshifting the d-band center and increasing H intermediate adsorption on the active sites. Furthermore, the N, P-doped carbon matrix protects the Mo-doped FeP nanoparticles from aggregation, exposing more active sites during hydrogen production. This work provides new avenues for applying highly efficient metal phosphide catalysts for the HER. [ABSTRACT FROM AUTHOR]

A new strategy for doping selenium and phosphide in hollow N-doped carbon nanobox (N-CNB)-based porous electrospun N-doped carbon nanofibers (CNFs) was developed. First, lightweight N-CNBs were produced. Then, a hybrid of N-CNBs and CNFs (CNBs/CNFs) was prepared using electrospinning/carbonization techniques. Eventually, P and Se atoms were doped into CNBs/CNFs using a thermal treatment approach to prepare Se/P@CNBs/CNFs. The electrocatalytic capability of the Se/P@CNBs/CNFs composite toward H2O2 oxidation was investigated for H2O2 sensing, which showed performance in a linear range from 200 μM to 1800 μM with a high sensitivity of 171 μA mM−1 cm−2 and a limit of detection (LOD) of 58 μM (S/N = 3). In addition, the ability of Se/P@CNBs/CNFs toward H2O2 sensing in human serum was studied. These results indicated the excellent electrocatalytic performance of the as-prepared Se/P@CNBs/CNFs, which could be related to the unique hollow CNBs/CNFs doped with P and Se elements with a mesoporous structure, the open channels for effective H2O2 diffusion, fast mass/electron transport, and synergistic effect between the P and Se and CNBs/CNFs. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOF) were used as templates to prepare transition metal sulfides and phosphides in order to expose the active site of the material to a greater extent. Utilizing the synergistic effect of bimetals, Ni2+ and Mo6+ were selected as metal ion centers and trimesic acid was selected as the ligand to prepare NiMo-MOFs by the hydrothermal method. Then, NiMo-P, NiMo-S and NiMo-P/S were prepared using NiMo-MOFs as the precursor, and the preparation conditions of the abovementioned hybrids were optimized through linear sweep voltammetry. The results show that when the molar ratio of NiMo-MOF to NaH2PO2 is 1: 5, and the as-prepared NiMo-P is further doped with S in a proportion of 1: 1, the overpotential of the final NiMo-P/S hybrid is 313 mV at a current density of 10 mA cm-2, and its electrochemical impedance (Rct), Tafel slope and electrochemical active surface areas are 22.38 Ω, 63.8 mV dec-1, and 707.5 cm-2, respectively. The optimized NiMo-P/S hybrid provides more active sites and reaction areas along with good stability, which is conducive to promoting the kinetics of the oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Recently, many studies have been done on MXene (2D titanium carbide) for energy storage applications. It possesses outstanding features like hydrophobicity, conductivity, and particularly strong surface redox reactivity, which are essential for energy storage applications. Despite these exceptional properties, MXene's electrochemical performance is significantly impacted by certain deficiencies, such as the inability to assemble MXene sheets. To prevent MXene sheets from restacking, the spaces between them must be filled with an appropriate material. Metal-organic frameworks (MOFs) for electrochemical applications have also been extensively studied. Due to their high crystallinity, porous structure, and substantial surface area, MOFs find diverse applications, but their efficacy as electrode materials is hindered by a lower specific capacity and charging/discharging rate. Addressing these limitations, combining MOFs with suitable materials is preferred for enhanced performance. This study suggests an innovative approach: a composite between Cu-BTC MOF and N-MXene. By shortening both the ion/electron diffusion pathways and improving the electroactive sites, the prevention of MXene sheet restacking was achieved, leading to exceptional specific and rate capacity in the composite with MOFs. The Cu-BTC/N-MXene-decorated electrode exhibited energy and power density reaching approximately 65.23 W h kg-1 and 923 W kg-1 in a two-electrode (real device) configuration. Cu-BTC/N-MXene//N-MXene retained 99% of its capacity and a coulombic efficiency of 92% after 8000 alternate GCD cycles. The findings of this investigation highlight the significant potential of employing the innovative electrode material Cu-BTC/N-MXene for supercapattery applications. [ABSTRACT FROM AUTHOR]

Cellulose nanofiber (CNF) is an environmentally friendly material with a high specific surface area, which is an ideal candidate for cathode catalysts in zinc–air batteries (ZABs). However, untreated CNF-based carbon materials suffer from low intrinsic activity and fewer micro-mesopores. Herein, we developed an N-doped porous carbon aerogel from CNF and graphite phase carbon nitride (g-C3N4) via hydrothermal pretreatment and the carbonization process. The CNF can serve as the skeleton of the aerogel that leads to an interconnected porous structure, while g-C3N4 guarantees the in situ N doping and the formation of more nanopores. Therefore, the as-prepared carbon aerogel exhibits excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances owing to the successful N doping with sufficient graphite-N and pyridine-N active sites (69.1%) and high specific surface areas (785.4 m2 g−1). The assembled ZABs with a carbon aerogel deliver a specific capacity of 790 mA h g−1 and an energy density of 945.6 W h kg−1 with a long-term stability over 100 h. This work opens a new avenue for the effective conversion of abundant biomass into bifunctional air cathodes for energy-related applications. [ABSTRACT FROM AUTHOR]

Medium entropy alloys, consisting of four elements in close to isotropic proportions, have attracted a great deal of attention because of their unique properties (excellent strength, corrosion resistance, etc.). Here, we present a series of quaternary medium entropy alloy FeCoNiW electrocatalysts loaded onto nitrogen-doped carbon (NC) skeletons. The prepared medium entropy alloy catalysts have excellent OER catalytic activity and stability. In alkaline media, the FeCoNiW-NC electrocatalysts annealed at 350 °C were able to achieve an overpotential as low as 225 mV at a current density of 10 mA cm−2, which is 55 mV lower than that of the commercial RuO2, while it has a smaller Tafel slope of 54 mV dec−1. The introduction of W leads to a change in the electronic structure of the FeCoNi alloy and increases the specific surface area of the catalyst, exhibiting excellent performance. This work contributes to the exploration of OER catalysts by opening new avenues for the design of efficient and economical OER electrocatalysts. [ABSTRACT FROM AUTHOR]

It is still a challenge to explore durable and highly efficient non-precious metal-based electrocatalysts, especially transition metal phosphides (TMPs), with favorable nanoarchitectures towards the hydrogen evolution reaction (HER). Herein, we demonstrate an effective NaCl hard template strategy combined with subsequent high temperature phosphorization to prepare MoP nanocrystals encapsulated in N-doped three-dimensional carbon networks (MoP/NC). Due to the excellent integration of uniform electrocatalytic active constituents and a unique porous conductive carbonaceous framework, the hierarchical heterostructures exhibit robust HER activity to achieve 10 mA cm−2 at relatively low overpotential in acidic (130 mV) and alkaline (150 mV) media, respectively, and present superior cyclability and durability to bulk MoP. This work provides a versatile route to design and construct multi-dimensional TMP/carbonaceous matrix composites to be applied in the electrocatalytic HER and even other energy storage and conversion applications. [ABSTRACT FROM AUTHOR]

Black phosphorene (BP) is a metal-free two-dimensional photocatalyst with potential for visible-light-driven photocatalytic H2 evolution. However, its inert basal plane toward the HER hinders its practical application. To overcome this problem, we design a novel nonprecious metal–nonmetal co-doping method of BP to activate its inert basal plane and improve photocatalytic HER performance. Through density functional theory (DFT) calculations, we systematically investigate the photocatalytic performance of nonprecious metal and nonmetal co-doped BPs. Our results show that V–N co-doped BP exhibits excellent thermodynamic stability, suitable band structure, improved carrier separation, superior adsorption and dissociation energies and enhanced visible-light absorption coefficient. Importantly, V–N co-doping successfully activates the inert basal plane of BP, allowing it to drive the HER under illumination (ΔGH = −0.12 eV). This study highlights the potential of nonprecious metal–nonmetal co-doping to enhance the photocatalytic activity of BP, providing invaluable insights for advancing the field of co-doped BP in photocatalysis. [ABSTRACT FROM AUTHOR]

Direct urea fuel cells (DUFCs) offer an environmentally friendly, and cost-effective way to turn wastewater into energy. However, the paucity of efficient, cost-effective, and electrochemically stable urea electro-oxidation reaction (UOR) specific electrocatalysts continues to impede the design and development of practically useful DUFCs. The present work explores the design and development of N-doped graphene (NGr)-supported platinum (Pt) plus silver (Ag) alloy nanohybrids (PtxAg100−x-NGr) as potential UOR electrocatalysts. Our results suggest that the electrocatalytic performance of PtxAg100−x-NGr is very sensitive toward the composition of this nanohybrid. The nanohybrid with a Pt : Ag ratio of 1 : 1, referred to as Pt50Ag50-NGr in the MS, exhibits the best UOR electrocatalytic performance. The Pt50Ag50-NGr composite exhibits a Tafel slope of just ∼12.92 mV dec−1, and a UOR-specific activity of nearly 4028 mA cm−2 mg cat−1 at 1.673 V (vs. RHE) and requires an overpotential of just 1.617 V (vs. RHE) to maintain a UOR specific current density of 10 mA cm−2. These parameters qualify the Pt50Ag50-NGr as a promising anode material for DUFCs. This we demonstrate through the design of a Pt50Ag50-NGr anode-based prototype urea-H2O2 fuel cell that delivers an open circuit voltage (OCV) of 750 mV and a power density of ∼5.75 mW cm−2. [ABSTRACT FROM AUTHOR]

Although graphite phase carbon nitride (CN) photocatalysts possess great potential in solving the global energy crisis, their photocatalytic activity is severely affected by sluggish charge dissociation/migration efficiency, a high carrier recombination rate, low active site exposure, and limited visible-light harvesting. Herein, a sulfur doped CN (x-DZCN) was tailored via one-step thermally-induced polymerization of urea with dithizone, which could evolve hydrogen at a rate of 1930 μmol g−1 h−1 (7.1 times higher than that of a single CN). The characterization of the catalyst confirmed that the boosted photocatalytic activity originated from the improved specific surface area from 46 to 61 m2 g−1, broadened visible light harvesting from 470 nm to over 600 nm, more negative conduction band (shift up of 0.54 eV), and promoted charge behavior (improved exciton dissociation and carrier migration efficiency, as well as suppressed carrier recombination capacity). The stable and efficient photocatalytic hydrogen evolution performance verifies the feasibility and potential of this photocatalyst in clean energy production. [ABSTRACT FROM AUTHOR]

The rational design of an active and stable electrocatalyst for the hydrogen evolution reaction (HER) is demonstrated as a major challenge for the renewable energy-driven water-splitting process. Herein, a unique structure of nitrogen-doped carbon-based Mo2C@TiO2 (NC/Mo2C@TiO2) was synthesized via controlling incorporation of TiO2 nanoparticles in the carbonization process to achieve promising electrocatalytic activity towards the HER. The electronic structure of Mo2C nanodots was regulated by TiO2 and nitrogen-doped carbon, thus exposing abundant active sites for the HER. Electrochemical measurement shows that the NC/Mo2C@TiO2 electrocatalyst has a low overpotential of 167 mV at 10 mA cm−2 with a Tafel slope of 158 mV dec−1 in 1 M KOH. The electrocatalyst shows excellent stability with a slightly declined current density of 92.88% after 35 h of operation because of the involvement of TiO2. Moreover, the design concept can be extended to developing other transition metal carbide electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of efficient and stable catalysts for the oxygen reduction reaction (ORR) is crucial to enable practical large-scale application of Zn–air batteries (ZABs). This study investigates the utilization of N, S co-doped coal-based activated carbon materials, synthesized through facile reactions, which exhibit high specific surface area and abundant active sites. The results of material characterization and experiments indicate that co-doping with N and S can effectively modify the charge distribution of coal-based activated carbon materials, increase the active sites, and ultimately enhance their performance in the oxygen reduction reaction (ORR). The N, S-AC catalyst exhibits remarkable catalytic activity for the ORR in alkaline electrolytes, demonstrating a high half-wave potential (E1/2 = 0.79 V), ultimate current density (jL = 6.35 mA cm−2) and stability, as well as considerable tolerance to methanol. The N, S-AC-based ZAB also demonstrates exceptional performance, achieving a maximum power density of 142 mW cm−2 and a specific capacity of 804 mA h gZn−1. This study not only simplifies the preparation process for heteroatom-doped coal-based activated carbon catalysts but also explores practical applications for ZABs. [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) are widely used as catalysts for overall water splitting due to their maximum utilization of surface active sites. However, until now, efficient SACs for water splitting are still lacking. Herein, a systematic screening of the overall water splitting performance of Fe, Co, and Ni atoms anchored on M2C, nitrogen modified M2C, and Fe and N co-modification M2C MXenes is performed by using first-principles calculations. The results show that Fe/Mo2C exhibits better hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances among the studied TM/Mo2C structures, with the corresponding value of ΔGH* and ηOER being 0.03 eV and 0.66 V, respectively. In addition, there is an obvious volcanic curve relationship between the d-band center (εd) of TM/M2C and the overpotential of the OER (ηOER). Low N doping concentrations (25%) can also adjust the HER and OER activity of M2C. Interestingly, N doping and Fe loading co-modification Mo2C (Fe/N-Mo2C) shows the best HER and OER properties among the studied TM/N-Mo2C structures, with the corresponding ΔGH* and ηOER being 0.01 eV and 0.39 V, respectively. The thermodynamics binding energy and dynamics simulation results reveal that TM/M2C and TM/N-M2C are dynamically stable at the reaction temperature. This work shows that Fe/N-Mo2C can be a potential catalyst for overall water splitting. [ABSTRACT FROM AUTHOR]

Developing durable and efficient catalysts for the hydrogen evolution reaction (HER) is of great importance for hydrogen production. By judiciously doping nonmetallic elements into transition metal electrocatalysts, the respective electronic configurations of the catalysts can be effectively adjusted, and their activity levels can be improved. Herein, B-doped CoP/nitrogen-doped carbon (B-CoP/NC) was constructed by subjecting B-doped Co-Prussian blue analogue to a phosphidation process. Benefiting from an enhanced electrochemical active area, improved conductivity, and suitable electron distribution caused by the introduction of B, the defective nanocubes of the B-CoP/NC catalyst needed overpotentials of only 158 and 234 mV to achieve current densities of, respectively, 10 and 100 mA cm−2 and showed a low Tafel slope of 67 mV dec−1. This work has supplied a general route involving NaBH4 pretreatment for introducing B into transition metal phosphide and has offered a method for designing HER catalysts. [ABSTRACT FROM AUTHOR]

Catalysts with high catalytic activity and low cost are extremely significant for hydrogen production by water cracking. In this work, through simple electrospinning and carbonization methods, Ru with excellent catalytic activity is dispersed onto Fe4C to form Ru–Fe4C nanoparticles loaded on N-doped carbon nanofibers (Ru–Fe4C/NCNF), so that Ru can expose more active sites and thus improve HER catalytic activity. Meanwhile, the addition of low-cost Fe can reduce the use of noble metal Ru, thereby reducing the catalyst cost. On the other hand, the prepared Ru–Fe4C/NCNF can be used as a self-supporting working electrode and shows good stability. The experimental results show that the prepared Ru–Fe4C/NCNF can drive a current density of 10 mA cm−2 with only 106 mV in 1 M KOH, and more importantly, only 254 mV can produce a current density of 100 mA cm−2. At the same time, it shows excellent stability after continuously working for 100 h at a current density of 100 mA cm−2. This work provides a new thought to synthesize economical catalysts with high catalytic activity. [ABSTRACT FROM AUTHOR]

Rational construction of low-cost, high-activity electrocatalysts is essential for hydrogen production from electrolytic water. Herein, a Co0.75Mo3S3.75/MoS2 heterogeneous interfacial structure and nitrogen and carbon co-doped on a carbon cloth hydrogen evolution electrocatalyst (NC-Co-MoS2/CC-450) was synthesized by a simple drop coating and pyrolysis method. NC-Co-MoS2/CC-450 exhibits excellent hydrogen evolution performance, achieving a current density of 10 mA cm−2 at only 56 mV, while exhibiting a Faraday efficiency of 99.85% and good stability. Moreover, at high current densities (100 mA cm−2 and 200 mA cm−2), only 155 mV and 220 mV overpotentials are required, respectively, with a small Tafel slope (69.2 mV dec−1). This is due to the intrinsic nitrogen and carbon doped multiphase composite Co0.75Mo3S3.75/MoS2 heterogeneous interface synergistic crystalline-amorphous material system, which generates a large number of lattice defects and exposes a richer active area, accelerating the efficiency of hydrogen evolution and hydrogen desorption. The hydrogen evolution performance of NC-Co-MoS2/CC-450 prepared by the rational design is significantly better than that of many previously reported molybdenum-based catalysts, and this work suggests a further way to continue the development of low-cost and efficient alkaline hydrogen evolution electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of high performance electrocatalysts is pivotal for electrocatalytic hydrogen evolution reaction (HER). In this work, a nitrogen doped carbon dot (NDCD) supported palladium copper nanoparticle composite (n-PdCu@NDCDs) was synthesized and effectively utilized as an electrocatalyst. The as-synthesized n-PdCu@NDCD composite was duly characterized by regular analytical techniques (HR-TEM, EDS, XPS, XRD, FT-IR, and Raman). Moreover, the electrocatalytic activity of n-PdCu@NDCDs was studied by linear sweep voltammetry (LSV), Tafel, and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M aqueous H2SO4. The overpotential at high current density of n-PdCu@NDCDs was much lower than that of PdCu, NDCDs, and bare GC. The EIS studies showed that the charge transfer resistance of n-PdCu@NDCDs decreased from 1864 to 503.4 Ω cm−2 on increasing the HER overpotentials, which confirmed the excellent conductivity and activity of the composite. Thus the present work confirms the utility of the n-PdCu@NDCD composite as an electrocatalyst for the HER. [ABSTRACT FROM AUTHOR]

Developing cost-efficient, stable, and environmentally benign electrocatalysts is a strong enticement towards the realization of commercial clean energy devices. Ni–Co-based systems have been particularly interesting owing to the well-recognized catalytically active redox pairs of Co3+/Co2+ and Ni3+/Ni2+. The sulphides of the latter have been frequently investigated catalyst systems with a particular focus on the sulphide-based heterostructured unions that offer better interfacial contacts. In this study, we report an electrochemically efficient hetero-catalyst (Co9S8–NiCo2S4/N-rGO) consisting of a binary sulphide–sulphide system, Co9S8/NiCo2S4, anchored on N-doped rGO) through a simple sulphurization strategy. The hetero-catalyst with ideally integrated interfaces ensures facile interfacial electron movement within the sulphide components and the rGO backbone, rendering excellent electrocatalytic properties. The highly exposed surface and N-doping in rGO further offer to expedite the mass transfer rate, and the suitable integration with the latter reduces the electrolyte corrosion to improve the activity and stability. Co9S8–NiCo2S4/N-rGO exhibits impressive bifunctional activity with an overpotential requirement of 149 mV for a benchmark hydrogen evolution reaction (HER) current of 10 mA cm−2 and an overpotential requirement of 230 mV for a benchmark oxygen evolution reaction (OER) current of 20 mA cm−2. The enhanced HER and OER kinetics are further supported by low Tafel slopes of 89 mV dec−1 and 93 mV dec−1, respectively. The full cell constructed from Co9S8–NiCo2S4/N-rGO exhibits water-splitting to the tune of 10 mA cm−2 and 100 mA cm−2 at cell voltages of 1.59 V and 2.1 V, respectively. Moreover, excellent catalytic stability was demonstrated with negligible loss in the catalytic performance for 15 continuous hours of electrocatalysis. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water-splitting cells and metal–air batteries. Cobalt phosphide nanomaterials have been reported as promising OER electrocatalysts. Herein, the rational design of advanced nanostructures for nitrogen doped and carbon coated cobalt phosphide hollow nanospheres (CoP@NC HNS) was highly desirable to optimize their electrocatalytic performance. SiO2 nanospheres were used as a sacrificial template for the synthesis of hollow nanospheres composed of ultrathin CoP@NC nanosheet arrays. The hollow nanostructure CoP@NC was coated with a layer of carbon material and the thickness of the shell was about 40 nm. The resultant CoP@NC HNS manifested high electrocatalytic activity towards the OER with low overpotential (320 mV, 10 mA cm−2), small Tafel slope (68 mV dec−1), and remarkable stability in alkaline electrolyte. Remarkably, the CoP@NC HNS still maintained an outstanding performance for the OER at 60 °C. [ABSTRACT FROM AUTHOR]

Developing noble-metal-free bifunctional electrocatalysts at an effective cost and with a high catalytic ability for hydrogen production via water-splitting is imperative, although a great bottleneck remains. Herein, we present a plasma engraving strategy to synthesize N-doped CoFeS on cobalt foam with a multi-interface and defect hierarchical structure. The N-doped CoFeS was synthesized using an ion exchange method to prepare the CoFe LDH precursor, followed by sulphidation and plasma-assisted engraving in nitrogen gas. The N-doped CoFeS requires an overpotential of 230 mV for the OER and 26 mV for the HER to reach a current density of 10 mA cm−2. It also shows an excellent catalytic activity towards overall water splitting, which requires a low voltage of 1.61 and 1.80 V to achieve a current density of 10 and 50 mA cm−2, respectively, in 1 M KOH. The super-catalytic properties can be attributed to the interface and defect structure, which induces a high intrinsic activity, a superior transfer coefficient, and abundant active sites. This work presents a novel approach to prepare noble-metal-free electrocatalyst with plenty of interface and defect sites for overall water splitting. [ABSTRACT FROM AUTHOR]

Among other factors, the electrochemical capacitor (EC) properties of graphene oxide (GO) are limited by conductivity issues emanating from high oxygen concentrations. Hence, innovative GO modifications, such as derivatisation and synthesising composites with conducting polymers, are required to boost the EC properties. This allows the exploitation of the low material cost associated with carbonaceous materials. Herein, the effect of temperature (70, 130 and 190 °C) on the hydrothermal treatment of a GO/urea mixture (to form nitrogen-doped reduced GO samples U70, U130 and U190 (N-RGO), respectively) was investigated in order to study the resulting physicochemical and EC properties of N-RGO in a K2SO4 electrolyte. Subsequently, the EC properties of the N-RGO obtained from the optimum temperature were investigated in composites with polyaniline (PANI). The functionality of the composites in the electrolytes, namely, K2SO4 (SO42− radius: 258 pm) versus KOH (OH− radius: 133 pm), was compared. The nitrogen at% in GO and N-RGO (U190) was 0.39 and 6.74%, respectively, with corresponding conductivities of 4.61 × 10−7 and 4.17 × 10−1 S cm−1. Compared with GO, U130 achieved the highest increase in specific capacitance (Cs) of 200 times at 10 mV s−1. The 5 wt% PANI composite displayed the highest enhancement of Cs of 14 032% at 50 mV s−1 and 4749% at 5 mV s−1 relative to N-RGO and PANI in K2SO4, respectively. The highest Cs values for NRGO-PANI composites in KOH were more than double those of K2SO4. This work demonstrates that the hydrothermal treatment temperature tailors the physicochemical properties of the doped GO and, together with the anion size of the electrolyte and PANI wt%, synergistically tunes the EC properties of the ultimate PANI-N-RGO composite. [ABSTRACT FROM AUTHOR]

Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo2N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo2N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo2N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (‖ΔGH*‖), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo2N to form stable structures of Co doped Mo2N (Co–Mo2N) and Cu doped Mo2N (Cu–Mo2N). Compared with pristine Mo2N, both Cu–Mo2N and Co–Mo2N demonstrated a much improved cocatalytic effect over g-C3N4 in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co–Mo2N with the highest conductivity and lowest ‖ΔGH*‖ illustrated the best cocatalytic effect, and the H2 production performance (367.8 μmol g−1 h−1) of Co–Mo2N/g-C3N4 achieved was 10 and 5 times higher than those of Mo2N/g-C3N4 and Cu–Mo2N/g-C3N4. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application. [ABSTRACT FROM AUTHOR]

Using metal-free heteroatom-doped carbon material electrocatalysts with high efficiency and low cost for oxygen reduction reaction (ORR) to replace Pt or its alloys is a major task for promoting the reaction efficiency of fuel cells. Here, we report the rational design of three-dimensional (3D) ultra-thin N-doped porous graphene-like carbon (NPC) catalyst based on amino acid zinc chelates containing ligand bonds as both templates and nitrogen sources. During high-temperature annealing treatment, the evaporation of Zn is beneficial to produce a hierarchical porous structure, higher specific surface area and more defect sites. A 3D ultra-thin graphene-like covalently crosslinked polymer with a multilayer network structure was formed by a condensation reaction of amino acid Zn complexes. Under the optimized pyrolysis temperature, the as-obtained NPC-1050 catalyst has a higher defect density and graphitic-N/pyridinic-N ratio, and exhibits an excellent ORR catalytic performance. The half-wave potential, onset potential and limiting current density are 0.878 mV, 0.970 mV and 5.64 mA cm−2, respectively. In addition, it also showed a competitive performance when compared to commercial Pt/C catalysts in Zn-air batteries. The present route may provide new insights into the synthesis of polypeptide or protein metal complexes, and their application in energy fields. [ABSTRACT FROM AUTHOR]

The water splitting reaction has the potential to be a sustainable and environmentally friendly way of producing hydrogen as a fuel source, which is an important step in reducing our reliance on fossil fuels and mitigating climate change. Currently, most commonly used catalysts for water splitting are based on precious metals such as platinum and iridium, which are expensive and scarce. Therefore, finding new catalysts that are low-cost, abundant and efficient is of great importance for making water splitting economically viable on a large scale. It was found that pairing up Co nanoparticles (NPs) with MoCx boosted the hydrogen evolution reaction (HER) activity by more than 2-fold (η10 = 130 mV, Tafel slope = 156.08 mV dec−1), compared with the pure Co NPs supported on N-doped carbon (η10 = 337 mV) under alkaline medium conditions. Its activity is comparable to those of Pt single-atom catalysts (SACs) supported on a mesoporous carbon matrix. The good activity may be due to the modification of the D-band of Co by Mo doping and the relatively high electrochemically active surface area (ECSA) of 477.25 cm2, which is comparable to those of Ru SAC materials. [ABSTRACT FROM AUTHOR]

The effect of element doping can effectively promote the surface activity of catalysts due to the optimization of the electronic structure and surface charge distribution. Herein, we report the effect of Fe-doped NiCoP on the hydrogen evolution reaction to regulate the hydrogen adsorption energy and Gibbs free energy of hydrogen adsorption. [ABSTRACT FROM AUTHOR]

In the current work, TiO2 nanoarchitectures with high surface area and charge density have been synthesized by a facile hydrothermal method and further modified via co-doping with a transition metal (nickel) and rare-earth metals (europium, cerium, and holmium). Different characterization tools (i.e., XRD, BET surface area, FTIR, Raman, PL, SEM, TEM, XAS, XPS, and DRS) have been used to check the effect of co-doping on the electrical, morphological, and structural properties of the TiO2 nanoarchitectures. The FTIR, Raman, and XRD results confirmed the successful co-doping of the TiO2 nanoarchitectures. The high surface area of the co-doped nanoarchitectures as compared to undoped and singly doped TiO2 was confirmed from BET measurements. The presence of dopants in various oxidation states was further elucidated via XPS and XAS studies. FE-SEM and TEM revealed the formation of interconnected, mesoporous-type nanoarchitectures, with particle sizes less than 100 nm. The supercapacitive behavior of synthesized nanoarchitectures was evaluated by performing cyclic voltammetry, linear scan voltammetry, galvanostatic charge–discharge, and electrochemical impedance measurements. The specific capacitance values (Csp) indicate that the co-doping of rare-earth metals into the TiO2 structure results in enhanced capacitance of the target materials. The highest capacitive behavior was observed in the Ni-Ho-3 sample (740 F g−1), followed by Ni-Eu-3 (630 F g−1), Ni-Ce-3 (552 F g−1), and Ni-5 (545 F g−1), as compared to that of pure TiO2 (240 F g−1). Furthermore, the Ni-Ho-3 electrode also showed better cyclic stability with 97% capacity retention after 1000 cycles at a high current density of 5 A g−1. The water oxidation studies also showed that all the doped TiO2 nano-catalysts show enhanced oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity. The OER overpotential values at 10 mA cm−2 for Ni-Eu-3, Ni-5, Ni-Ce-3, and Ni-Ho-3 are 520, 550, 600, and 620 mV, respectively. The Tafel slopes of undoped TiO2, Ni-5, Ni-Eu-3, Ni-Ce-3, and Ni-Ho-3 are measured to be 151, 143, 134, 141, and 137 mV dec−1, respectively. The smallest Tafel slope of Ni-Eu-3 indicated its highest OER efficiency among all the selected samples. As compared with the other samples, Ni-Ho-3 sample also showed a lower value for the Tafel slope. The superior performance of co-doped nanoarchitectures was credited to the development of mesoporous structures with more electroactive sites, high charge density, and better charge transfer (EIS results). [ABSTRACT FROM AUTHOR]

The preparation of green hydrogen by electrolyzing water has shown great application prospects, and the noble metal Pt as a catalyst for the hydrogen evolution reaction (HER) is one of the main factors hindering its large-scale development. Therefore, efforts to develop low-cost catalysts are currently on-going in many laboratories. Herein, we used hydroxylated carbon nanotubes as starting materials and doped them with heteroatoms (S and N) to create catalytic active sites. In order to further improve the catalytic performance of the material, ruthenium nanoparticles were embedded on the nanotubes to obtain an excellent HER catalyst (Ru@S/N/CNT). We have systematically analyzed its morphology, chemical composition and electrochemical properties. The results show that its HER catalytic performance is outstanding, even higher than that of commercial Pt/C. Ru@S/N/CNTs show excellent catalytic performance under both acidic and alkaline conditions, which is due to the synergistic effect of the doping strategy and ruthenium nanoparticles. In 0.5 M H2SO4, the overpotential is 68 mV (10 mA cm−2), and the Tafel slope is only 44 mV dec−1. In 1 M KOH, the overpotential is only 9 mV at 10 mA cm−2, and the Tafel slope is only 37 mV dec−1. The doping strategy can only improve the catalytic performance of the material to a certain extent, and the SCN− poisoning experiment shows that dispersed ruthenium nanoparticles play a major role in HER catalysis. [ABSTRACT FROM AUTHOR]