RESUMEN

Heteroatom doping is considered a typical method for improving the electrochemical properties of composites. In this work, the multi-component oxide catalyst (Ni(VO3)2 and Co2V2O7 on Ni foam, referred to as NiCoVOx@NF) is formed by hydrothermal doping of V element into NiCo-based precursors followed by co-oxidation. In the catalyst NiCoVOx@NF, all three components of Ni, Co and V are particularly tightly coordinated, exhibiting an integrated structure of keel flower-like arrays. The catalyst NiCoVOx@NF's contact surface with water is increased thanks to this unusual structure, exposing a high number of active sites. Furthermore, NiCoVOx@NF owns efficient electronic pathways, which greatly enhances the electron transport ability. To generate a current density of 10 mA cm-2 for hydrogen evolution reaction, just a 107 mV overpotential is required. The electrode exhibits a low overpotential of 217 mV to deliver 50 mA cm-2 for oxygen evolution reaction. In addition, the total water splitting performance of NiCoVOx@NF is also excellent, which could be achieved by only one 1.5 V AA battery. This study provides a feasible heteroatom doping route to design bifunctional catalysts with improved performances.

RESUMEN

Combining the self-sacrifice of a highly crystalline substance to design a multistep chain reaction towards ultrathin active-layer construction for high-performance water splitting with atmospheric-temperature conditions and an environmentally benign aqueous environment is extremely intriguing and full of challenges. Here, taking cobalt carbonate hydroxides (CCHs) as the initial crystalline material, we choose the Lewis acid metal salt of Fe(NO3 )3 to induce an aqueous-phase chain reaction generating free CO3 2- ions with subsequent instant FeCO3 hydrolysis. The resultant ultrathin (∼5 nm) amorphous Fe-based hydroxide layer on CCH results in considerable activity in catalyzing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), yielding 10/50 mA ⋅ cm-2 at overpotentials of 230/266.5 mV for OER and 72.5/197.5 mV for HER. The catalysts can operate constantly in 1.0 M KOH over 48 and 45 h for the OER and HER, respectively. For bifunctional catalysis for alkaline electrolyzer assembly, a cell voltage as low as 1.53 V was necessary to yield 10 mA cm-2 (1.7 V at 50 mA cm-2 ). This work rationally builds high-efficiency electrochemical bifunctional water-splitting catalysts and offers a trial in establishing a controllable nanolevel ultrathin lattice disorder layer through an atmospheric-temperature chemical route.

RESUMEN

Engineering lattice strain, especially when it combines with the lattice distortion and vacancy (LDV) induced by locally unbalanced Coulomb forces (LUCFs), can improve the local coordination environment of atoms to achieve synergistically active sites and dynamic regulation of electrocatalysts, which are beneficial to high-performance bifunctional water splitting. Considering that Ni-based selenides possess abundant variable valence states, the Nb/Fe diatomic heterogeneous spin states are purposely introduced to produce LUCFs for improving the electronic coordination environment of the materials. The as-prepared Nb/Fe co-doped Ni-Ses (NbFe-NixSey) electrocatalyst exhibits the prominent oxygen and hydrogen evolution reaction (OER/HER) properties, with low overpotentials of 237 and 226 mV at 50 mA cm-2, respectively. The alkaline water electrolyzer with NbFe-NixSey as both anodic and cathodic electrodes only requires a cell potential of 1.7 V to reach 50 mA cm-2 in a continuous operation of 50 h. This work provides a new insight to regulate the electronic structure of advanced catalyst materials at the atomic level through LUCFs-induced LDV and further push forward the energy conversion technology.

RESUMEN

Lattice disorder engineering on highly crystalline texture toward high-efficiency N2-to-NH3 electrocatalysis is tremendously challenging. Here, abundant lattice disturbances were established on an ultrafine Nb2O5 nanoparticle by Cu substitution. Cu-Nb2O5 anchored on a carbon material (Cu-Nb2O5@C) exhibits excellent activity and high selectivity for N2 electroreduction to NH3 with a yield rate of 28.07 µg h-1 mg-1 and a faradaic efficiency (FE) of 13.25% at -0.2 V vs. reversible hydrogen electrode (RHE) in acidic electrolyte. Cu-Nb2O5@C presents superb durability with no obvious change in catalyst constituents and structure after N2 reduction as confirmed by ex situ characterization studies. The excellent catalytical performance should originate from structural superiority of lattice turbulence for more active sites and optimized electronic state as well as good conductivity of carbon support. Meanwhile, in neutral electrolyte, the NH3 FE also reaches up to 10.29% at the same potential.

RESUMEN

Interface engineering has proven an effective strategy for designing high-performance water-oxidation catalysts. Interface construction combining the respective advantages of amorphous and crystalline phases, especially embedding amorphous phases in crystalline lattices, has been the focus of intensive research. This study concerns the construction of an amorphous-crystalline FeOOH phase boundary (a-c-FeOOH) by structural evolution of iron oxyhydroxide-isolated Fe(OH)3 precursors from one-step hydrothermal synthesis. a-c-FeOOH demonstrates superb electrocatalytic activity for the oxygen evolution reaction (OER) with overpotential of 330 mV to drive a current density of 300 mA cm-2 in 1.0 m KOH, which is among the best OER catalysts and much better than the pristine amorphous or crystalline FeOOH alone. Density functional theory calculations reveal that the high-density a-c phase boundaries play a critical role in determining high OER activity.

RESUMEN

Electrochemical reduction of CO2 into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO2 reduction reaction to convert CO2 into alcohols with high selectivity. In 0.5 m KHCO3 , such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE CH 3 OH ) up to 80.2 %, with a total FE CH 3 OH + C 2 H 5 OH of 94.3 % at -0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO2 toward CH3 OH owing to the synergistic effect of two adjacent Fe atoms, and the potential-determining step is the hydrogenation process of *CO.

RESUMEN

Amorphous transition-metal (hydr)oxides have proven to be the most promising oxygen evolution reaction (OER) electrocatalysts. Here, a facile and novel strategy for the generation of porous amorphous cobalt oxide through one-step treatment of the cobalt carbonate hydroxide precursor with concentrated sulfuric acid has been reported. Benefiting from the optimized amorphous structure, the prepared catalyst exhibits an excellent water-oxidation activity in an alkaline electrolyte with the demand of 50 mV less overpotential at 10 mA cm-2 compared to that of highly-crystallized Co3O4. Compared with the 400 °C annealing process for Co3O4, the ultrafast acid treatment process within 10 seconds at room-temperature for achieving such amorphous cobalt oxide demonstrates tremendous convenience. More impressively, after continuous testing for 60 h at an overpotential of 370 mV, it still maintains a porous configuration as well as ∼92% of the original current density. Our findings not only present a high-efficiency OER electrocatalyst, but also provide a methodology with broad applicability toward the systematic study of other non-crystal oxides for green energy applications.

RESUMEN

Conversion of naturally abundant nitrogen to ammonia is a key (bio)chemical process to sustain life and represents a major challenge in chemistry and biology. Electrochemical reduction is emerging as a sustainable strategy for artificial nitrogen fixation at ambient conditions by tackling the hydrogen- and energy-intensive operations of the Haber-Bosch process. However, it is severely challenged by nitrogen activation and requires efficient catalysts for the nitrogen reduction reaction. Here we report that a boron carbide nanosheet acts as a metal-free catalyst for high-performance electrochemical nitrogen-to-ammonia fixation at ambient conditions. The catalyst can achieve a high ammonia yield of 26.57 µg h-1 mg-1cat. and a fairly high Faradaic efficiency of 15.95% at -0.75 V versus reversible hydrogen electrode, placing it among the most active aqueous-based nitrogen reduction reaction electrocatalysts. Notably, it also shows high electrochemical stability and excellent selectivity. The catalytic mechanism is assessed using density functional theory calculations.

RESUMEN

An amorphous Co-Mo-B film on a Ti mesh (Co-Mo-B/Ti) is fabricated via one-step electrodeposition exhibiting a dramatically enhanced hydrogen evolution reaction (HER) performance in alkaline media. To attain a current density of 20 mA cm-2, such Co-Mo-B/Ti demands only an overpotential of 110 mV, 190 mV lower than that of the counterpart Co-B/Ti, with strong electrochemical durability to maintain its catalytic activity for at least 32 h.

RESUMEN

The discovery of stable and noble-metal-free catalysts toward efficient electrochemical reduction of nitrogen (N2 ) to ammonia (NH3 ) is highly desired and significantly critical for the earth nitrogen cycle. Here, based on the theoretical predictions, MoS2 is first utilized to catalyze the N2 reduction reaction (NRR) under room temperature and atmospheric pressure. Electrochemical tests reveal that such catalyst achieves a high Faradaic efficiency (1.17%) and NH3 yield (8.08 × 10-11 mol s-1 cm-1 ) at -0.5 V versus reversible hydrogen electrode in 0.1 m Na2 SO4 . Even in acidic conditions, where strong hydrogen evolution reaction occurs, MoS2 is still active for the NRR. This work represents an important addition to the growing family of transition-metal-based catalysts with advanced performance in NRR.

RESUMEN

In spite of recent advances in the synthesis of transition metal phosphide nanostructures, the simple fabrication of hierarchical arrays with more accessible active sites still remains a great challenge. In this Communication, we report a space-confined phosphidation strategy toward developing hierarchical CoP nanosheet@microwire arrays on nickel foam (CoP NS@MW/NF) using a Co(H2PO4)2·2H3PO4 microwire array as the precursor. The thermally stable nature of the anion in the precursor is key to hierarchical nanostructure formation. When used as a 3D electrode for water oxidation electrocatalysis, such CoP NS@MW/NF needs an overpotential as low as 296 mV to drive a geometrical catalytic current density of 100 mA cm-2 in 1.0 M KOH, outperforming all reported Co phosphide catalysts in alkaline media. This catalyst also shows superior long-term electrochemical durability, maintaining its activity for at least 65 h. This study offers us a general method for facile preparation of hierarchical arrays for applications.

RESUMEN

It is highly desired but still remains challenging to design and develop a Co-based nanoparticle-encapsulated conductive nanoarray at room temperature for high-performance water oxidation electrocatalysis. Here, it is reported that room-temperature anodization of a Co(TCNQ)2 (TCNQ = tetracyanoquinodimethane) nanowire array on copper foam at alkaline pH leads to in situ electrochemcial oxidation of TCNQ- into water-insoluable TCNQ nanoarray embedding Co(OH)2 nanoparticles. Such Co(OH)2 -TCNQ/CF shows superior catalytic activity for water oxidation and demands only a low overpotential of 276 mV to drive a geometrical current density of 25 mA cm-2 in 1.0 m KOH. Notably, it also demonstrates strong long-term electrochemical durability with its activity being retrained for at least 25 h, a high turnover frequency of 0.97 s-1 at an overpotential of 450 mV and 100% Faradic efficiency. This study provides an exciting new method for the rational design and development of a conductive TCNQ-based nanoarray as an interesting 3D material for advanced electrochemical applications.

RESUMEN

It is highly desired to develop efficient earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. In this communication, we report the in situ electrochemical conversion of a nanoarray of Cu(tetracyanoquinodimethane), Cu(TCNQ), an inorganic-organic hybrid, on Cu foam into CuO nanocrystals confined in a highly conductive nanoarray via anode oxidation. As a 3D catalyst electrode, the resulting CuO-TCNQ/CF shows high OER activity and demands an overpotential of only 317 mV to drive a geometrical catalytic current density of 25 mA cm-2. Notably, this catalyst also demonstrates strong long-term electrochemical durability. This study provides us with a universal strategy toward topotactic room-temperature preparation of conductive nanoarrays with confined transition metal nanocatalysts for practical applications.

RESUMEN

It is fascinating to design and synthesize high-efficiency and noble-metal-free alkaline oxygen evolution reaction (OER) electrocatalysts. In this Communication, we describe the one-step hydrothermal synthesis of a WO3 nanoarray directly grown on conductive carbon cloth (WO3/CC) for efficient water oxidation in 1.0 M KOH. As a monolithically integrated array catalyst, WO3/CC exhibits superior OER activity demanding overpotential as low as 280 mV to afford a benchmarking catalytic current density of 10 mA cm-2. It is worth noting that WO3/CC also possesses strong electrochemical durability with 95% Faradaic yields.

RESUMEN

Efficient oxygen evolution reaction (OER) catalysts are highly desired to improve the overall efficiency of electrochemical water splitting. We develop a benzoate anion-intercalated layered cobalt hydroxide nanobelt array on nickel foam (benzoate-Co(OH)2 /NF) through a one-pot hydrothermal process. As a 3 D electrode, benzoate-Co(OH)2 /NF with an expanded interlayer spacing (14.72 Å) drives a high OER catalytic current density of 50 mA cm-2 at an overpotential of 291 mV, outperforming its carbonate anion-intercalated counterpart with a lower interlayer spacing of 8.81 Š(337 mV overpotential at 50 mA cm-2 ). Moreover, this benzoate-Co(OH)2 /NF can maintain its catalytic activity for 21 h.

Asunto(s)

RESUMEN

The exploration of high-performance and earth-abundant water oxidation catalysts operating under mild conditions is highly attractive and challenging. In this communication, core-shell CoFe2O4@Co-Fe-Bi nanoarray on carbon cloth (CoFe2O4@Co-Fe-Bi/CC) was successfully fabricated by in situ surface amorphization of CoFe2O4 nanoarray on CC (CoFe2O4/CC). As a 3D water oxidation electrode, CoFe2O4@Co-Fe-Bi/CC shows outstanding activity with an overpotential of 460 mV to drive a geometrical catalytic current density of 10 mA cm-2 in 0.1 M potassium borate (pH 9.2). Notably, it also demonstrates superior long-term durability for at least 20 h with 96% Faradic efficiency. Density functional theory calculations indicate that the conversion from OOH* to O2 is the rate-limiting step and the high water oxidation activity of CoFe2O4@Co-Fe-Bi/CC is associated with the lower free energy of 1.84 eV on a Co-Fe-Bi shell.

RESUMEN

There is an urgent demand to develop earth-abundant electrocatalysts for efficient and durable water oxidation under mild conditions. A nickel-substituted cobalt-borate nanowire array is developed on carbon cloth (Ni-Co-Bi/CC) via oxidative polarization of NiCo2 S4 nanoarray in potassium borate (K-Bi). As a bimetallic electrocatalyst for water oxidation, such Ni-Co-Bi/CC is superior in catalytic activity and durability in 0.1 m K-Bi (pH: 9.2), with a turnover frequency of 0.33 mol O2 s-1 at the overpotential of 500 mV and nearly 100% Faradaic efficiency. To drive a geometrical catalytic current density of 10 mA cm-2 , it only needs overpotential of 388 mV, 34 mV less than that for Co-Bi/CC, outperforming reported non-noble-metal catalysts operating under benign conditions. Notably, its activity is maintained over 80 000 s. Density functional theory calculations suggest that the O* to OOH* conversion is the rate-determining step and Ni substitution decreases the free energy on Co-Bi from 2.092 to 1.986 eV.

RESUMEN

The exploration of high-performance and cost-effective water oxidation catalysts operating under mild conditions is still urgent and challenging. In this communication, a nickel-borate nanoarray supported on carbon cloth (Ni-Bi/CC) has been fabricated through oxidative polarization of a nickel oxide nanoarray on CC (NiO/CC) in a borate electrolyte (pH 9.2). As a 3D electrode, this Ni-Bi/CC exhibits superior catalytic activity for water oxidation in 0.1 M potassium borate (K-Bi) solution, yielding a geometrical catalytic current density of 10 mA cm-2 at an overpotential of 470 mV. Notably, this electrode also demonstrates outstanding long-term electrochemical durability for 25 h with 100% Faradaic efficiency.

RESUMEN

Dispersion in water of two-dimensional (2D) nanosheets is conducive to their practical applications in fundamental science communities due to their abundance, low cost, and ecofriendliness. However, it is difficult to achieve stable aqueous 2D material suspensions because of the intrinsic hydrophobic properties of the layered materials. Here, we report an effective and economic way of producing various 2D nanosheets (h-BN, MoS2, MoSe2, WS2, and graphene) as aqueous dispersions using carbon quantum dots (CQDs) as exfoliation agents and stabilizers. The dispersion was prepared through a liquid phase exfoliation. The as-synthesized stable 2D nanosheets based dispersions were characterized by UV-vis, HRTEM, AFM, Raman, XPS, and XRD. The solutions based on CQD decorated 2D nanosheets were utilized as aqueous lubricants, which realized a friction coefficient as low as 0.02 and even achieved a superlubricity under certain working conditions. The excellent lubricating properties were attributed to the synergetic effects of the 2D nanosheets and CQDs, such as good dispersion stability and easy-sliding interlayer structure. This work thus proposes a novel strategy for the design and preparation of high-performance water based green lubricants.

RESUMEN

Herein, a conceptually new and straightforward aqueous route is described for the synthesis of hydroxyl- and amino-functionalized boron nitride quantum dots (BNQDs) with quantum yields (QY) as high as 18.3 % by using a facile bottom-up approach, in which a mixture of boric acid and ammonia solution was hydrothermally treated in one pot at 200 °C for 12 h. The functionalized BNQDs, with excellent photoluminescence properties, could be easily dispersed in an aqueous medium and applied as fluorescent probes for the detection of ferrous (Fe2+ ) and ferric (Fe3+ ) ions with excellent selectivity and low detection limits. The mechanisms for the hydrothermal reaction and fluorescence quenching were also simulated by using density functional theory (DFT), which confirmed the feasibility and advantages of this strategy. It provides a scalable and eco-friendly method for preparation of BNQDs with good dispersability and could also be generalized to the synthesis of other 2D quantum dots and nanoplates.