Polymeric carbon nitride (C3N4) has emerged as the most promising candidate for metal-free photocatalysts but is plagued by low activity due to the poor quantum efficiency and low specific surface ...area. Exfoliation of bulk crystals into ultrathin nanosheets has proven to be an effective and widely used strategy for enabling high photocatalytic performances; however, this process is complicated, time-consuming, and costly. Here, we report a simple bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors, alcohol molecules intercalation, and subsequent thermal-induced exfoliation and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution activity than bulk counterpart. Furthermore, we find that both the high activity and selectivity for the oxidative coupling of amines to imines can be obtained under visible light that surpass those of other metal-free photocatalysts so far.
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IJS, KILJ, NUK, PNG, UL, UM
Overall water splitting driven by a low voltage is crucial for practical H2 evolution, but it is challenging. Herein, anion‐modulation of 3D Ni–V‐based transition metal interstitial compound (TMIC) ...heterojunctions supported on nickel foam (Ni3N‐VN/NF and Ni2P‐VP2/NF) as coupled hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for efficient overall water splitting is demonstrated. The heterointerface in Ni3N‐VN has a suitable H* absorption energy, being favorable for enhancing HER activity with onset overpotential (ηonset) of zero and Tafel slope of 37 mV dec−1 in 1 m KOH (close to that of Pt/C/NF). For the OER, the synergy of Ni2P‐VP2 with oxide species can give enhanced activity with ηonset of 220 mV and Tafel slope of 49 mV dec−1. The good activity is ascribed to heterointerface for activating the intermediates, good conductivity of TMICs for electron‐transfer, and porous structure facilitation of mass‐transport. Additionally, the minimal mutual influence of Ni3N‐VN/NF and Ni2P‐VP2/NF allows easy coupling for efficient overall water splitting with a low driving voltage (≥1.43 V), a voltage of 1.51 V at 10 mA cm−2, and remarkable durability for 100 h. It can be driven by a solar cell (1.5 V), indicating its potential to store intermittent energy.
An anion‐modulation strategy is presented to create 3D Ni–V interstitial compound heterojunctions (Ni3N–VN/nickel foam (NF) and Ni2P‐VP2/NF). The excellent hydrogen evolution reaction (HER) activity of Ni3N–VN/NF and oxygen evolution reaction (OER) activity of Ni2P–VP2/NF and minimal mutual influence make them easy to couple to achieve overall water splitting with a low driving voltage and remarkable stability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Developing non‐precious‐metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn–air batteries. Co‐based catalysts ...have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co–N–C nanosheets supported by carbon felts (Co/Co–N–C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self‐template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co–N–C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X‐ray absorption fine spectroscopy and X‐ray photoelectron spectroscopy certify the formation of Co (mainly Co0) and the Co–N–C (mainly Co2+ and Co3+) structure. As the air‐cathode, the assembled aqueous Zn–air battery exhibits a small charge–discharge voltage gap (0.82 V@10 mA cm−2) and high power density of 132 mW cm−2, outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn–air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X‐ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co–N–C cathode in Zn–air battery.
A 3D hierarchical self‐supported electrode composed of Co nanoislands and Co–N–C nanosheets is developed for highly efficient bifunctional oxygen reduction reaction/oxygen evolution reaction catalysts toward both liquid‐ and solidstate Zn–air batteries. Operando X‐ray absorption fine‐structure is combined with density functional theory calculation to further elucidate the active sites of oxygen reactions at the Co/Co–N–C cathode in Zn–air batteries.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Phosphorus‐modified tungsten nitride/reduced graphene oxide (P‐WN/rGO) is designed as a high‐efficient, low‐cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on ...rGO is first synthesized by using the H3PO4(W3O9)4 cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P‐WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec−1, and a large exchange current density of 0.35 mA cm−2 in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm−2, while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.
Boosting HER activity by phosphorus modification of tungsten nitride/reduced graphene oxide leads to a low‐cost, high‐performance, non‐noble metal electrocatalyst for the hydrogen evolution reaction. The catalyst has a very small onset overpotential, a low Tafel slope, a large exchange current density in acid, and was stable in accelerated durability testing.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Herein, we present a new strategy for the synthesis of 2D porous MoP/Mo2N heterojunction nanosheets based on the pyrolysis of 2D PMo12O403−‐melamine (PMo12‐MA) nanosheet precursor from a polyethylene ...glycol (PEG)‐mediated assembly route. The heterostructure nanosheets are ca. 20 nm thick and have plentiful pores (<5 nm). These structure features offer advantages to promote the HER activity, including the favorable water dissociation kinetics around heterojunction as confirmed by theoretical calculations, large accessible surface of 2D nanosheets, and enhanced mass‐transport ability by pores. Consequently, the 2D porous MoP/Mo2N heterojunction nanosheets exhibit excellent HER activity with low overpotentials of 89, 91 and 89 mV to achieve a current density of 10 mA cm−2 in alkaline, neutral and acidic electrolytes, respectively. The HER performance is superior to the commercial Pt/C at a current density >55 mA cm−2 in neutral medium and >190 mA cm−2 in alkaline medium.
2D porous MoP/Mo2N heterojunction nanosheets have been created based on a PEG‐mediated assembly strategy, which exhibit outstanding performance for HER over wide pH ranges even out‐performing the Pt/C benchmark at large current density. A series of tests and DFT calculations shows the synergy of the heterojunctions, pores and 2D nanosheets for promoting the HER performance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Developing the efficient and low-cost electrocatalysts for overall water splitting is of the great importance for the production of H2. The popular bi-functional catalysts usually shown good activity ...for one half reaction at expense of the activity for another half-reaction, thus given a moderate performance for overall water splitting. In this paper, we have reported on integrating the active OER (Ni3N) and HER (NiMoN) components as Ni3N-NiMoN heterostructures for the effective overall water splitting. The heterostructures were constructed by the controllable nitridation of the Ni-Mo-O precursor anchored on carbon cloth (CC) under NH3 atmosphere. The micro-structures of the catalyst could be tuned by regulating the surface properties of CC and the calcination temperature. Under optimized condition, the Ni3N-NiMoN catalysts exhibited good catalytic activity for both OER and HER in alkaline electrolyte. The catalysts can achieve a current density of 10mAcm−2 at an overpotential of 31mV for HER, being close to Pt catalyst. Also, it only requiring an overpotential of 277mV to reach current density of 10mAcm−2 for OER. Moreover, the cell assembled by the identical Ni3N-NiMoN as both the cathode and anode needs only a cell voltage of 1.54V to achieve current density of 10mAcm−2. The superior performance of Ni3N-NiMoN heterostructures can be ascribed to the following points: 1) the simultaneous presence of active OER and HER components and the promoted action each other in the heterostructures, and 2) the exposure of the abundant active sites in the sheet-like structure assembled by the nanoparticles.
The OER-active Ni3N and HER-active NiMoN have been integrated as Ni3N-NiMoN heterostructures anchored on carbon cloth for the high-effective overall water splitting. The catalysts can achieve a current density of 10mAcm−2 at an overpotential of 31mV for HER and an overpotential of 277mV for OER. The cell assembled by Ni3N-NiMoN heterostructures as both the cathode and anode only needs a cell voltage of 1.54V to achieve 10mAcm−2 for overall water splitting. Display omitted
•The active OER and HER components are integrated as Ni3N-NiMoN heterostructures.•The heterostructures show good performance for both HER and OER.•The heterostructures exhibit superior performance for overall water splitting.•The origin of superior performance of the heterostructures is elucidated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An advanced supercapacitor material based on nitrogen‐doped porous graphitic carbon (NPGC) with high a surface area was synthesized by means of a simple coordination–pyrolysis combination process, in ...which tetraethyl orthosilicate (TEOS), nickel nitrate, and glucose were adopted as porogent, graphitic catalyst precursor, and carbon source, respectively. In addition, melamine was selected as a nitrogen source owing to its nitrogen‐enriched structure and the strong interaction between the amine groups and the glucose unit. A low‐temperature treatment resulted in the formation of a NPGC precursor by combination of the catalytic precursor, hydrolyzed TEOS, and the melamine–glucose unit. Following pyrolysis and removal of the catalyst and porogent, the NPGC material showed excellent electrical conductivity owing to its high crystallinity, a large Brunauer–Emmett–Teller surface area (SBET=1027 m2 g−1), and a high nitrogen level (7.72 wt %). The unusual microstructure of NPGC materials could provide electrochemical energy storage. The NPGC material, without the need for any conductive additives, showed excellent capacitive behavior (293 F g−1 at 1 A g−1), long‐term cycling stability, and high coulombic efficiency (>99.9 % over 5000 cycles) in KOH when used as an electrode. Notably, in a two‐electrode symmetric supercapacitor, NPGC energy densities as high as 8.1 and 47.5 Wh kg−1, at a high power density (10.5 kW kg−1), were achieved in 6 M KOH and 1 M Et4NBF4‐PC electrolytes, respectively. Thus, the synthesized NPGC material could be a highly promising electrode material for advanced supercapacitors and other conversion devices.
Energy storage made easy: Nitrogen‐doped porous graphitic carbon (NPGC) materials with large surface areas (1027 m2 g−1) and high nitrogen levels (7.72 wt %) were produced by a robust coordination–pyrolysis process (see figure). The prepared NPGC materials exhibit excellent capacitive behavior, superior cycling stability, and high energy and power densities as electrode material for advanced supercapacitors.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Paired electroreduction and electrooxidation of organics with water as a feedstock to produce value-added chemicals is meaningful. A comprehensive understanding of reaction mechanism is critical for ...the catalyst design and relative area development. Here, we have systematically studied the mechanism of the paired electroreduction and electrooxidation of organics on Fe-Mo-based phosphide heterojunctions. It is shown that active H* species for organic electroreduction originate from water. As for organic electrooxidation, among various oxygen species (OH*, OOH*, and O*), OH* free radicals derived from the first step of water dissociation are identified as active species. Furthermore, explicit reaction pathways and their paired advantages are proposed based on theoretical calculations. The paired electrolyzer powered by a solar cell shows a low voltage of 1.594 V at 100 mA cm
, faradaic efficiency of ≥99%, and remarkable cycle stability. This work provides a guide for sustainable synthesis of various value-added chemicals via paired electrocatalysis.
Sheet-like graphitic carbon with a porous structure can provide low-resistant pathways and short ion-diffusion channels for energy storage, and thus is expected to be an excellent material for ...high-power supercapacitors. Herein, porous graphene-like nanosheets (PGNSs) with a large surface area were synthesized for the first time viaan easy and cost-effective SAG (simultaneous activation-graphitization) route from renewable biomass waste coconut shell. In the synthesis, the graphitic catalyst precursor (FeCl sub(3)) and activating agent (ZnCl sub(2)) were introduced simultaneously into the skeleton of the coconut shell through coordination of the metal precursor with the functional groups in the coconut shell, thus making simultaneous realization of activation and graphitization of the carbon source under heat treatment. Notably, the iron catalyst in the framework of the coconut shell can generate a carburized phase which plays a key role in the formation of a graphene-like structure during the pyrolytic process. Our results indicated that PGNSs possess good electrical conductivity due to the high graphitic degree, exceptionally high Brunauer-Emmett-Teller surface area (S sub(BET) = 1874 m super(2) g super(-1)) and large pore volume (1.21 cm super(3) g super(-1)). While being used as a supercapacitor electrode without the use of any conductive additives, PGNSs exhibit a high specific capacitance of 268 F g super(-1), much higher than that of activated carbon (210 F g super(-1)) fabricated by only activation and graphitic carbon (117 F g super(-1)) by only graphitization at 1 A g super(-1). Also, PGNSs show superior cycle durability and Coulombic efficiency over 99.5% after 5000 cycles in KOH. Remarkably, in an organic electrolyte, PGNSs also display an outstanding capacitance of 196 F g super(-1) at 1 A g super(-1). An energy density of up to 54.7 W h kg super(-1) could be achieved at a high power density of 10 kW kg super(-1). The SAG strategy developed here would provide a novel route for low-cost and large-scale production of PGNS electrode materials for high-power supercapacitors.
Development of cost-effective and highly-efficient bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is crucial for overall water splitting in practical ...utilization. Herein, we proposed a novel non-noble metal bifunctional HER/OER electrocatalyst by synergistically coupling a dual-active Co-based heterojunction (Co-CoO) with high conductive and stable two-dimensional Ti
3
C
2
-MXene (defined as Co-CoO/Ti
3
C
2
-MXene). A series of characterizations and theoretical calculations verify that the synergistic effect of metallic Co with HER activity and CoO with OER performance leads to superb bifunctional catalytic performance, and Ti
3
C
2
-MXene can enhance electrical conductivity and prevent the aggregation of the Co-based catalysts, thereby improving both the activity and stability. Co-CoO/Ti
3
C
2
-MXene presents low onset potential (
η
onset
) of 8 mV and Tafel slope of 47 mV·dec
−1
for HER (close to that of Pt/C) and
η
onset
of 196 mV and Tafel slope of 47 mV·dec
−1
for OER (superior to that of RuO
2
). Assembled as an electrolyzer, Co-CoO/Ti
3
C
2
-MXene shows a low voltage of 1.55 V at 10 mA·cm
−2
, high Faradaic efficiency and remarkable stability. It can be driven by a solar cell of ∼ 1.55 V for consecutive production of hydrogen and oxygen gases.
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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
