Nickel-based catalysts are most commonly used in industrial alkaline water electrolysis. However, it remains a great challenge to address the sluggish reaction kinetics and severe deactivation ...problems of hydrogen evolution reaction (HER). Here, we show a Cu-doped Ni catalyst implanted with Ni-O-VOx sites (Ni(Cu)VOx) for alkaline HER. The optimal Ni(Cu)VOx electrode exhibits a near-zero onset overpotential and low overpotential of 21 mV to deliver -10 mA cm
, which is comparable to benchmark Pt/C catalyst. Evidence for the formation of Ni-O-VOx sites in Ni(Cu)VOx is established by systematic X-ray absorption spectroscopy studies. The VOx can cause a substantial dampening of Ni lattice and create an enlarged electrochemically active surface area. First-principles calculations support that the Ni-O-VOx sites are superactive and can promote the charge redistribution from Ni to VOx, which greatly weakens the H-adsorption and H
release free energy over Ni. This endows the Ni(Cu)VOx electrode high HER activity and long-term durability.
Abstract
Selective two-electron (2e
−
) oxygen reduction reaction (ORR) offers great opportunities for hydrogen peroxide (H
2
O
2
) electrosynthesis and its widespread employment depends on ...identifying cost-effective catalysts with high activity and selectivity. Main-group metal and nitrogen coordinated carbons (M-N-Cs) are promising but remain largely underexplored due to the low metal-atom density and the lack of understanding in the structure-property correlation. Here, we report using a nanoarchitectured Sb
2
S
3
template to synthesize high-density (10.32 wt%) antimony (Sb) single atoms on nitrogen- and sulfur-codoped carbon nanofibers (Sb-NSCF), which exhibits both high selectivity (97.2%) and mass activity (114.9 A g
−1
at 0.65 V) toward the 2e
−
ORR in alkaline electrolyte. Further, when evaluated with a practical flow cell, Sb-NSCF shows a high production rate of 7.46 mol g
catalyst
−1
h
−1
with negligible loss in activity and selectivity in a 75-h continuous electrolysis. Density functional theory calculations demonstrate that the coordination configuration and the S dopants synergistically contribute to the enhanced 2e
−
ORR activity and selectivity of the Sb-N
4
moieties.
The development of novel single atom catalyst (SAC) is highly desirable in organic synthesis to achieve the maximized atomic efficiency. Here, a Co‐based SAC on nitrogen‐doped graphene (SACo@NG) with ...high Co content of 4.1 wt% is reported. Various characterization results suggest that the monodispersed Co atoms are coordinated with N atoms to form robust and highly effective catalytic centers to activate peroxymonosulfate (PMS) for organic selective oxidation. The catalytic performance of the SACo@NG/PMS system is conducted on the selective oxidation of benzyl alcohol (BzOH) showing high efficiency with over 90% conversion and benzaldehyde selectivity within 180 min under mild conditions. Both radical and non‐radical processes occurred in the selective oxidation of BzOH, but the non‐radical oxidation plays the dominant role which is accomplished by the adsorption of BzOH/PMS on the surface of SACo@NG and the subsequent electron transfer through the carbon matrix. This work provides new insights to the preparation of efficient transition metal‐based single atom catalysts and their potential applications in PMS mediated selective oxidation of alcohols.
A novel cobalt single‐atom catalyst (SAC) is prepared on nitrogen‐doped graphene support with scalable mass through a feasible method. The atomic Co atoms are bonded with N atoms in the graphene matrix to form highly stabilized configurations. The Co SAC shows extraordinary performance in the selective oxidation of benzyl alcohol into benzaldehyde with activated peroxymonosulfate via radical and non‐radical pathways.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
A practical high-specific-energy Li metal battery requires thin (≤20 μm) and free-standing Li metal anodes, but the low melting point and strong diffusion creep of lithium metal impede their ...scalable processing towards thin-thickness and free-standing architecture. In this paper, thin (5 to 50 μm) and free-standing lithium strips were achieved by mechanical rolling, which is determined by the in situ tribochemical reaction between lithium and zinc dialkyldithiophosphate (ZDDP). A friction-induced organic/inorganic hybrid interface (~450 nm) was formed on Li with an ultra-high hardness (0.84 GPa) and Young’s modulus (25.90 GPa), which not only enables the scalable process mechanics of thin lithium strips but also facilitates dendrite-free lithium metal anodes by inhibiting dendrite growth. The rolled lithium anode exhibits a prolonged cycle lifespan and high-rate cycle stability (in excess of more than 1700 cycles even at 18.0 mA cm
−2
and 1.5 mA cm
−2
at 25 °C). Meanwhile, the LiFePO
4
(with single-sided load 10 mg/cm
2
) ||Li@ZDDP full cell can last over 350 cycles with a high-capacity retention of 82% after the formation cycles at 5 C (1 C = 170 mA/g) and 25 °C. This work provides a scalable approach concerning tribology design for producing practical thin free-standing lithium metal anodes.
The increasing use of zinc oxide nanoparticles (ZnO-NPs) in various commercial products is prompting detailed investigation regarding the fate of these materials in the environment. There is, ...however, a lack of information comparing the transformation of ZnO-NPs with soluble Zn2+ in both soils and plants. Synchrotron-based techniques were used to examine the uptake and transformation of Zn in various tissues of cowpea (Vigna unguiculata (L.) Walp.) exposed to ZnO-NPs or ZnCl2 following growth in either solution or soil culture. In solution culture, soluble Zn (ZnCl2) was more toxic than the ZnO-NPs, although there was substantial accumulation of ZnO-NPs on the root surface. When grown in soil, however, there was no significant difference in plant growth and accumulation or speciation of Zn between soluble Zn and ZnO-NP treatments, indicating that the added ZnO-NPs underwent rapid dissolution following their entry into the soil. This was confirmed by an incubation experiment with two soils, in which ZnO-NPs could not be detected after incubation for 1 h. The speciation of Zn was similar in shoot tissues for both soluble Zn and ZnO-NPs treatments and no upward translocation of ZnO-NPs from roots to shoots was observed in either solution or soil culture. Under the current experimental conditions, the similarity in uptake and toxicity of Zn from ZnO-NPs and soluble Zn in soils indicates that the ZnO-NPs used in this study did not constitute nanospecific risks.
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IJS, KILJ, NUK, PNG, UL, UM
The development of reliable and safe high‐energy‐density lithium‐ion batteries is hindered by the structural instability of cathode materials during cycling, arising as a result of detrimental phase ...transformations occurring at high operating voltages alongside the loss of active materials induced by transition metal dissolution. Originating from the fundamental structure/function relation of battery materials, the authors purposefully perform crystallographic‐site‐specific structural engineering on electrode material structure, using the high‐voltage LiNi0.5Mn1.5O4 (LNMO) cathode as a representative, which directly addresses the root source of structural instability of the Fd3¯m structure. By employing Sb as a dopant to modify the specific issue‐involved 16c and 16d sites simultaneously, the authors successfully transform the detrimental two‐phase reaction occurring at high‐voltage into a preferential solid‐solution reaction and significantly suppress the loss of Mn from the LNMO structure. The modified LNMO material delivers an impressive 99% of its theoretical specific capacity at 1 C, and maintains 87.6% and 72.4% of initial capacity after 1500 and 3000 cycles, respectively. The issue‐tracing site‐specific structural tailoring demonstrated for this material will facilitate the rapid development of high‐energy‐density materials for lithium‐ion batteries.
Crystallographic‐site‐specific structural engineering is performed on the cathode material structure for lithium‐ion batteries, aiming at the root causes of the instability based on the fundamental structure/function relationship. The high‐voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode with Fd3¯m space group symmetry is employed as a representative, of which two issue‐involved crystallographic sites are directly and simultaneously addressed, contributing to an extraordinarily excellent battery performance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Iron single atom catalysts (Fe SACs) are the best‐known nonprecious metal (NPM) catalysts for the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs), but their ...practical application has been constrained by the low Fe SACs loading (<2 wt%). Here, a one‐pot pyrolysis method is reported for the synthesis of iron single atoms on graphene (FeSA‐G) with a high Fe SAC loading of ≈7.7 ± 1.3 wt%. The as‐synthesized FeSA‐G shows an onset potential of 0.950 V and a half‐wave potential of 0.804 V in acid electrolyte for the ORR, similar to that of Pt/C catalysts but with a much higher stability and higher phosphate anion tolerance. High temperature SiO2 nanoparticle‐doped phosphoric acid/polybenzimidazole (PA/PBI/SiO2) composite membrane cells utilizing a FeSA‐G cathode with Fe SAC loading of 0.3 mg cm−2 delivers a peak power density of 325 mW cm−2 at 230 °C, better than 313 mW cm−2 obtained on the cell with a Pt/C cathode at a Pt loading of 1 mg cm−2. The cell with FeSA‐G cathode exhibits superior stability at 230 °C, as compared to that with Pt/C cathode. Our results provide a new approach to developing practical NPM catalysts to replace Pt‐based catalysts for fuel cells.
Fe single‐atom catalysts embedded in graphene with high atomic loading are successfully fabricated by an one‐pot synthesis method and demonstrate excellent activity and superior stability as nonprecious metal cathodes of PA/PBI/SiO2 composite membrane based high temperature polymer electrolyte membrane fuel cells, and deliver a peak power density of 325 mW cm−2 at 230 °C.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The anodic behaviour of a nickel electrode has been investigated in KOH electrolytes below and above the oxygen evolution potential. As the literature reports a wide range of behaviours, initial ...repetitive cyclic voltammetry in 1M KOH was compared to 30wt% KOH (i.e., that used in alkaline water electrolysers) and it was found that a process in addition to the normal α-Ni(OH)2/γ-NiOOH and β-Ni(OH)2/β-NiOOH occurs in the more concentrated electrolyte. It is also confirmed that the initial hydroxide layer formed anodically from metallic nickel is not α-Ni(OH)2, but a layer which is more readily reducible than α-Ni(OH)2. At higher potentials, while in-situ XAS suggested that γ-NiOOH is not transformed to any further phase up to 0.665V vs HgHgO in 1M KOH, after extensive OER (at least 40 hrs) in 30wt% at 50mAcm−2, an additional phase can be identified by cyclic voltammetry. Overall, during galvanostatic oxygen evolution, the nickel anodes follow an ageing behaviour characterised by a brief activation period, a short period of high activity (i.e., low overpotential) followed by deactivation and eventually stable but poor activity. While no clear evidence was obtained to identify the most active phase for oxygen evolution, it is likely that this is related to β-NiOOH and confined to the very surface of the electrode.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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