Two‐electron oxygen photoreduction to hydrogen peroxide (H2O2) is seriously inhibited by its sluggish charge kinetics. Herein, a polarization engineering strategy is demonstrated by grafting ...(thio)urea functional groups onto covalent triazine frameworks (CTFs), giving rise to significantly promoted charge separation/transport and obviously enhanced proton transfer. The thiourea‐functionalized CTF (Bpt‐CTF) presents a substantial improvement in the photocatalytic H2O2 production rate to 3268.1 µmol h−1 g−1 with no sacrificial agents or cocatalysts that is over an order of magnitude higher than unfunctionalized CTF (Dc‐CTF), and a remarkable quantum efficiency of 8.6% at 400 nm. Mechanistic studies reveal the photocatalytic performance is attributed to the prominently enhanced two‐electron oxygen reduction reaction by forming endoperoxide at the triazine unit and highly concentrated holes at the thiourea site. The generated O2 from water oxidation is subsequently consumed by the oxygen reduction reaction (ORR), thereby boosting overall reaction kinetics. The findings suggest a powerful functional‐groups‐mediated polarization engineering method for the development of highly efficient metal‐free polymer‐based photocatalysts.
(Thio)urea‐functionalized covalent triazine frameworks (CTFs) are rationally designed, showing an outstanding photocatalytic activity toward production of H2O2 in water (3268.1 μmol h−1 g−1 with a quantum yield of 8.6% at 400 nm for the thiourea‐functionalized CTF) via reducing molecular oxygen (O2). This is much higher than most of the reported metal‐free polymer‐based photocatalysts in nonsacrificial systems.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Development of efficient non-precious catalysts for seawater electrolysis is of great significance but challenging due to the sluggish kinetics of oxygen evolution reaction (OER) and the impairment ...of chlorine electrochemistry at anode. Herein, we report a heterostructure of Ni
3
S
2
nanoarray with secondary Fe-Ni(OH)
2
lamellar edges that exposes abundant active sites towards seawater oxidation. The resultant Fe-Ni(OH)
2
/Ni
3
S
2
nanoarray works directly as a free-standing anodic electrode in alkaline artificial seawater. It only requires an overpotential of 269 mV to afford a current density of 10 mA·cm
−2
and the Tafel slope is as low as 46 mV·dec
−1
. The 27-hour chronopotentiometry operated at high current density of 100 mA·cm
−2
shows negligible deterioration, suggesting good stability of the Fe·Ni(OH)
2
/Ni
3
S
2
@NF electrode. Faraday efficiency for oxygen evolution is up to ∼ 95%, revealing decent selectivity of the catalyst in saline water. Such desirable catalytic performance could be benefitted from the introduction of Fe activator and the heterostructure that offers massive active and selective sites. The density functional theory (DFT) calculations indicate that the OER has lower theoretical overpotential than Cl
2
evolution reaction in Fe sites, which is contrary to that of Ni sites. The experimental and theoretical study provides a strong support for the rational design of high-performance Fe-based electrodes for industrial seawater electrolysis.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Rational design and controllable synthesis of nanostructured materials with unique microstructure and excellent electrochemical performance for energy storage are crucially desired. In this paper, a ...facile method is reported for general synthesis of hierarchically core–shell structured Ni3S2@NiMoO4 nanowires (NWs) as a binder‐free electrode for asymmetric supercapacitors. Due to the intimate contact between Ni3S2 and NiMoO4, the hierarchical structured electrodes provide a promising unique structure for asymmetric supercapacitors. The as‐prepared binder‐free Ni3S2@NiMoO4 electrode can significantly improve the electrical conductivity between Ni3S2 and NiMoO4, and effectively avoid the aggregation of NiMoO4 nanosheets, which provide more active space for storing charge. The Ni3S2@NiMoO4 electrode presents a high areal capacity of 1327.3 µAh cm−2 and 67.8% retention of its initial capacity when current density increases from 2 to 40 mA cm−2. In a two‐electrode Ni3S2@NiMoO4//active carbon cell, the active materials deliver a high energy density of 121.5 Wh kg−1 at a power density of 2.285 kW kg−1 with excellent cycling stability.
A facile method for general synthesis of core–shell structured Ni3S2@NiMoO4 nanowires as a binder‐free electrode for asymmetric supercapacitors is described in this study. Due to the intimate contact between the materials, core–shell structured Ni3S2@NiMoO4 binder‐free electrodes provide a promising target structure for energy storage.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Transitional metal selenides have high conductivity, even metal quality, which makes them great for using as electrode materials for fabricating supercapacitors. Here, hierarchical Ni3Se2 ...nanosheet-on-nanorods on Ni foam (NSR-Ni3Se2/Ni) was fabricated by a facile three-dimensional (3D) substrate-assisted confinement assembly method, and used as a freestanding electrode material for hybrid supercapacitors (HSCs). In this design, metallic Ni3Se2 with hybrid 1D/2D architecture could effectively enhance the active specific surface area of electrode and improve space utilization, as well as significantly facilitate electrons transport, while Ni foam served as the Ni source of Ni3Se2 and provided 3D multi-electron transport channels, thus boosting the specific capacity. The constructed hierarchical NSR-Ni3Se2 electrode delivered a superior areal specific capacity of 1.068 mAh/cm2 (7.69 F/cm2) at 2 mA/cm2 and retained 68.2% of the initial capacity when the current density increases by 15 times. Furthermore, the as-assembled NSR-Ni3Se2 device exhibited an ultrahigh energy density of 56.4 Wh/kg and high power density of 4640.3 W/kg, and a capacity retention of 92.6% even after 6000 cycles.
A hierarchical Ni3Se2 nanosheet-on-nanorods core-shell structure functioning as a freestanding electrode material for hybrid supercapacitors was fabricated by a facile three-dimensional Ni foam substrate-assisted confinement assembly method, which showed efficient and robust capacitor performance. Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The development of efficient strategies to recycle lithium-ion battery (LIB) electrode materials is an important yet challenging goal for the sustainable management of battery waste. This work ...reports a facile and economically efficient method to convert spent cathode material, LiFePO
4
, into a high-performance NiFe oxy/hydroxide catalyst for the oxygen evolution reaction (OER). Herein, Ni-LiFePO
4
is synthesized
via
the wetness impregnation method and further evolves into defect-rich NiFe oxy/hydroxide nanosheets during the OER. The introduction of the Ni promoter together with
in situ
evolution strengthens the electronic interactions among the metal sites and creates an abundance of defects. Experimentally, the evolved Ni-LiFePO
4
delivers a low overpotential of 285 mV at 10 mA cm
−2
and a small Tafel slope of 45 mV dec
−1
, outperforming pristine LiFePO
4
and is even superior to the benchmark catalyst RuO
2
. Density functional theory (DFT) calculations reveal that the introduction of Ni effectively activates Fe sites by optimizing the free energy of the *OOH intermediate and that the abundance of oxygen defects facilitates the oxygen desorption step, synergistically enhancing the OER performance of LiFePO
4
. As a green and versatile method, this is a new opportunity for the scalable fabrication of excellent electrocatalysts based on spent cathode materials.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Borocarbonitride (BCN), in a mesoscopic asymmetric state, is regarded as a promising photocatalyst for artificial photosynthesis. However, BCN materials reported in the literature primarily consist ...of symmetric N-B3 units, which generate highly spatial coupled electron–hole pairs upon irradiation, thus kinetically suppressing the solar-to-chemical conversion efficiency. Here, we propose a facile and fast weak-field electro-flash strategy, with which structural symmetry breaking is introduced on key nitrogen sites. As-obtained double-substituted BCN (ds-BCN) possesses high-concentration asymmetric B2–N-C coordination, which displays a highly separated electron–hole state and broad visible-light harvesting, as well as provides electron-rich N sites for O2 affinity. Thereby, ds-BCN delivers an apparent quantum yield of 7.6% at 400 nm and a solar-to-chemical conversion efficiency of 0.3% for selective 2e-reduction of O2 to H2O2, over 4-fold higher than that of the traditional calcined BCN analogue and superior to the metal-free C3N4-based photocatalysts reported so far. The weak-field electro-flash method and as-induced catalytic site symmetry-breaking methodologically provide a new method for the fast and low-cost fabrication of efficient nonmetallic catalysts toward solar-to-chemical conversions.
A partially fluorinated, metal‐free, imine‐linked two‐dimensional triazine covalent organic framework (TF50‐COF) photocatalyst was developed. Fluorine (F)‐substituted and nonsubstituted units were ...integrated in equimolar amounts on the edge aromatic units, where they mediated two‐electron O2 photoreduction. F‐substitution created an abundance of Lewis acid sites, which regulated the electronic distribution of adjacent carbon atoms and provided highly active sites for O2 adsorption, and widened the visible‐light‐responsive range of the catalyst, while enhancing charge separation. Varying the proportion of F maximized the interlayer interactions of TF50‐COF, resulting in improved crystallinity with faster carrier transfer and robust photostability. The TF50‐COF catalyst demonstrates high selectivity and stability in O2 photoreduction into H2O2, with a high H2O2 yield rate of 1739 μmol h−1 g−1 and a remarkable apparent quantum efficiency of 5.1 % at 400 nm, exceeding the performance of previously reported nonmetal COF‐based photocatalysts.
A crystalline, partially fluorinated triazine covalent organic framework (COF) was constructed with broad visible‐light responsiveness, improved charge separation and transfer, and enhanced O2 affinity. The COF exhibited attractive photocatalytic activity, selectivity, and stability for H2O2 production under visible‐light irradiation, and with higher activity than previously reported nonmetal COF‐based photocatalysts.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The rational design and synthesis of hybrid-type electrode nanomaterials are significant for their diverse applications, including their potential usage as high-efficiency nanoarchitectures for ...supercapacitors (SCs) as a class of promising energy-storage systems for powering next-generation electric vehicles and electronic devices. Here, we reported a facile and controllable synthesis of core-shell NiS/Ni
3
S
2
@ NiWO
4
nanoarrays to fabricate a freestanding electrode for hybrid SCs. Impressively, the as-prepared freestanding NiS/Ni
3
S
2
@NiWO
4
electrode presents an ultrahigh areal capacity of 2032 µA h cm
−2
at 5 mA cm
−2
, and a capacity retention of 63.6% even when the current density increased up to 50 mA cm
−2
. Remarkably, the NiS/Ni
3
S
2
@NiWO
4
nanoarray-based hybrid SC delivers a maximum energy density of 1.283 mW h cm
−2
at 3.128 mW cm
−2
and a maximum power density of 41.105 mW cm
−2
at 0.753 mW h cm
−2
. Furthermore, the hybrid SC exhibits a capacity retention of 89.6% even after continuous 10,000 cycles, proving its superior stability. This study provides a facile pathway to rationally design a variety of core shell metal nanostructures for high performance energy storage devices.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Highlights
An efficient and general strategy for ultrafast synthesis of seven transition metal layered hydroxides on conductive substrates is proposed, which avoids the use of additional reagents, ...multiple steps and long production time in the traditional bottom-up method.
The whole synthesis process only takes as fast as approximately 13 s, and its synthesis rate reaches ~ 0.46 cm
2
s
−1
.
The NiCo LDH@CC as a demonstration example is selected as cathode material for aqueous alkaline Zn (micro-) battery, which exhibits an outstanding performance.
Efficient synthesis of transition metal hydroxides on conductive substrate is essential for enhancing their merits in industrialization of energy storage field. However, most of the synthetic routes at present mainly rely on traditional bottom-up method, which involves tedious steps, time-consuming treatments, or additional alkaline media, and is unfavorable for high-efficiency production. Herein, we present a facile, ultrafast and general avenue to synthesize transition metal hydroxides on carbon substrate within 13 s by Joule-heating method. With high reaction kinetics caused by the instantaneous high temperature, seven kinds of transition metal-layered hydroxides (TM-LDHs) are formed on carbon cloth. Therein, the fastest synthesis rate reaches ~ 0.46 cm
2
s
−1
. Density functional theory calculations further demonstrate the nucleation energy barriers and potential mechanism for the formation of metal-based hydroxides on carbon substrates. This efficient approach avoids the use of extra agents, multiple steps, and long production time and endows the LDHs@carbon cloth with outstanding flexibility and machinability, showing practical advantages in both common and micro-zinc ion-based energy storage devices. To prove its utility, as a cathode in rechargeable aqueous alkaline Zn (micro-) battery, the NiCo LDH@carbon cloth exhibits a high energy density, superior to most transition metal LDH materials reported so far.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Display omitted
•Ni3S2@Co(OH)2 nanowires grown on Ni foam is synthesized via a facile process.•The Ni3S2@Co(OH)2 electrode demonstrates high specific capacitance of 2139.4 F g−1.•An asymmetric ...supercapacitor with high energy density was successfully assembled.
Core-shell structured Ni3S2@Co(OH)2 nano-wires directly grown on Ni foam as a binder-free electrode for asymmetric supercapacitors are synthesized though a facile two-step process. This unique core–shell architecture consisting of ultrathin Co(OH)2 nano-sheets and Ni3S2 nano-wires exhibits significantly enhanced electrochemical capacitive performance. The Ni3S2@Co(OH)2 electrode demonstrates high specific capacitance of 2139.4 F g−1 at the current density of 2 mA cm−2, and retains capacitance of 1139.4 F g−1 at a much higher current density of 40 mA cm−2. An asymmetric supercapacitor using Ni3S2@Co(OH)2 as cathode and active carbon as anode is successfully assembled in a coin cell. The as-prepared cell delivers high-power density as high as 18.27 kW kg−1 at the energy density of 74.79 Wh kg−1 with good cycling stability, which shows its feasibility for many practical applications for energy storage. These results indicate that the newly developed core-shell architecture is an efficient way towards improve the electrochemical performance in various promising energy storage applications.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
