Efficient generation of hydrogen from water-splitting is an underpinning chemistry to realize the hydrogen economy. Low cost, transition metals such as nickel and iron-based oxides/hydroxides have ...been regarded as promising catalysts for the oxygen evolution reaction in alkaline media with overpotentials as low as ~200 mV to achieve 10 mA cm
, however, they are generally unsuitable for the hydrogen evolution reaction. Herein, we show a Janus nanoparticle catalyst with a nickel-iron oxide interface and multi-site functionality for a highly efficient hydrogen evolution reaction with a comparable performance to the benchmark platinum on carbon catalyst. Density functional theory calculations reveal that the hydrogen evolution reaction catalytic activity of the nanoparticle is induced by the strong electronic coupling effect between the iron oxide and the nickel at the interface. Remarkably, the catalyst also exhibits extraordinary oxygen evolution reaction activity, enabling an active and stable bi-functional catalyst for whole cell water-splitting with, to the best of our knowledge, the highest energy efficiency (83.7%) reported to date.
Electrocatalytic synergy is a functional yet underrated concept in electrocatalysis. Often, it materializes as intermetallic interaction between different metals. We demonstrate interphasic synergy ...in monometallic structures is as much effective. An interphasic synergy between Ni(OH)
and Ni-N/Ni-C phases is reported for alkaline hydrogen evolution reaction that lowers the energy barriers for hydrogen adsorption-desorption and facilitates that of hydroxyl intermediates. This makes ready-to-serve Ni active sites and allocates a large amount of Ni d-states at Fermi level to promote charge redistribution from Ni(OH)
to Ni-N/Ni-C and the co-adsorption of H
and OH
intermediates on Ni-N/Ni-C moieties. As a result, a Ni(OH)
@Ni-N/Ni-C hetero-hierarchical nanostructure is developed, lowering the overpotentials to deliver -10 and -100 mA cm
in alkaline media by 102 and 113 mV, respectively, compared to monophasic Ni(OH)
catalyst. This study unveils the interphasic synergy as an effective strategy to design monometallic electrocatalysts for water splitting and other energy applications.
Metal–organic framework (MOFs) two‐dimensional (2D) nanosheets have many coordinatively unsaturated metal sites that act as active centres for catalysis. To date, limited numbers of 2D MOFs ...nanosheets can be obtained through top‐down or bottom‐up synthesis strategies. Herein, we report a 2D oxide sacrifice approach (2dOSA) to facilely synthesize ultrathin MOF‐74 and BTC MOF nanosheets with a flexible combination of metal sites, which cannot be obtained through the delamination of their bulk counterparts (top‐down) or the conventional solvothermal method (bottom‐up). The ultrathin iron–cobalt MOF‐74 nanosheets prepared are only 2.6 nm thick. The sample enriched with surface coordinatively unsaturated metal sites, exhibits a significantly higher oxygen evolution reaction reactivity than bulk FeCo MOF‐74 particles and the state‐of‐the‐art MOF catalyst. It is believed that this 2dOSA could provide a new and simple way to synthesize various ultrathin MOF nanosheets for wide applications.
Think thin: The so‐called 2D oxide sacrifice approach is developed to coordinate the metal atoms of amorphous metal oxide nanosheets with ligands to synthesize metal–organic framework (MOF) nanosheets. The resulting ultrathin FeCo MOF‐74 nanosheets (2.6 nm) show an excellent oxygen evolution reaction (OER) activity owing to abundant coordinatively unsaturated metal sites and heteroatom synergy.
Nickel‐based electrocatalysts are promising candidates for oxygen evolution reaction (OER) but suffer from high activation overpotentials. Herein, in situ structural reconstruction of V‐doped Ni2P ...pre‐catalyst to form highly active NiV oxyhydroxides for OER is reported, during which the partial dissolution of V creates a disordered Ni structure with an enlarged electrochemical surface area. Operando electrochemical impedance spectroscopy reveals that the synergistic interaction between the Ni hosts and the remaining V dopants can regulate the electronic structure of NiV oxyhydroxides, which leads to enhanced kinetics for the adsorption of *OH and deprotonation of *OOH intermediates. Raman spectroscopy and X‐ray absorption spectroscopy further demonstrate that the increased content of active β‐NiOOH phase with the disordered Ni active sites contributes to OER activity enhancement. Density functional theory calculations verify that the V dopants facilitate the generation of *O intermediates during OER, which is the rate‐determining step for realizing efficient O2 evolution. Optimization of these properties endows the NiV oxyhydroxide electrode with a low overpotential of 221 mV to deliver a current density of 10 mA cm−2 and excellent stability in the alkaline electrolyte.
In situ electrochemical oxidation and etching of V‐doped Ni2P pre‐catalyst enables the formation of NiV oxyhydroxide electrocatalysts for highly efficient oxygen evolution reaction. The partial dissolution of V can create enlarged electrochemical surface areas, while the remaining V modulate the electronic structure and the adsorption energy of OER intermediates. The in situ reconstructed catalyst displays extraordinary catalytic performance and stability.
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.
By introducing chromium into a nickel–iron layered double hydroxide (LDH), a nickel iron chromium hydroxide nanomesh catalyst has been achieved on nickel foam substrate via electrodeposition followed ...by partial etching of chromium. The electrodeposited chromium acts as a sacrificial template to introduce holes in the LDH to increase the electrochemically active surface area, and the remaining chromium synergistically modulates the electronic structure of the composite. The obtained electrode shows extraordinary performance for oxygen evolution reaction and excellent electrochemical stability. The onset potential of the as-prepared electrode in 1 M KOH is only 1.43 V vs RHE, and the overpotential to achieve a high current density of 100 mA·cm–2 is only 255 mV, outperforming benchmark nonprecious NiFe hydroxide composite electrode in alkaline media.
Transition metal nitrogen carbon based single‐atom catalysts (SACs) have exhibited superior activity and selectivity for CO2 electroreduction to CO. A favorable local nitrogen coordination ...environment is key to construct efficient metal‐N moieties. Here, a facile plasma‐assisted and nitrogen vacancy (NV) induced coordinative reconstruction strategy is reported for this purpose. Under continuous plasma striking, the preformed pentagon pyrrolic N‐defects around Ni sites can be transformed to a stable pyridinic N dominant Ni‐N2 coordination structure with promoted kinetics toward the CO2‐to‐CO conversion. Both the CO selectivity and productivity increase markedly after the reconstruction, reaching a high CO Faradaic efficiency of 96% at mild overpotential of 590 mV and a large CO current density of 33 mA cm‐2 at 890 mV. X‐ray adsorption spectroscopy and density functional theory (DFT) calculations reveal this defective local N environment decreases the restraint on central Ni atoms and provides enough space to facilitate the adsorption and activation of CO2 molecule, leading to a reduced energy barrier for CO2 reduction.
A nitrogen vacancy (NV) induced coordinative reconstruction is realized, by increasing plasma treating time, to construct a defective and unsaturated Ni‐pyridinic N2 coordination structure with superior CO2 reduction activity. This local N environment decreases the restraint on central Ni atoms and provides enough space which favors the adsorption and activation of CO2 molecule, leading to a reduced energy barrier for CO2 reduction.
Water oxidation in all oxygenic photosynthetic organisms is catalysed by the Mn₄CaO₄ cluster of Photosystem II. This cluster has inspired the development of synthetic manganese catalysts for solar ...energy production. A photoelectrochemical device, made by impregnating a synthetic tetranuclear-manganese cluster into a Nafion matrix, has been shown to achieve efficient water oxidation catalysis. We report here in situ X-ray absorption spectroscopy and transmission electron microscopy studies that demonstrate that this cluster dissociates into Mn(II) compounds in the Nafion, which are then reoxidized to form dispersed nanoparticles of a disordered Mn(III/IV)-oxide phase. Cycling between the photoreduced product and this mineral-like solid is responsible for the observed photochemical water-oxidation catalysis. The original manganese cluster serves only as a precursor to the catalytically active material. The behaviour of Mn in Nafion therefore parallels its broader biogeochemistry, which is also dominated by cycles of oxidation into solid Mn(III/IV) oxides followed by photoreduction to Mn²⁺.
Aggregation induced photoluminescent quenching of graphene quantum dots (GQDs) is a well-known effect, although there are limited reports of multicolour light emissions from such aggregates. In the ...present work, we demonstrate a novel aggregation induced bathochromic shift in emission similar to J-aggregates observed in dye molecules. Nitrogen-doped graphene quantum dots (N-GQDs) prepared in the presence of diethylenetriamine show blue emission which is attributed to monomers at low concentration (58 μg/ml) while cyan (1.75 mg/ml), and greenish yellow (3.5 mg/ml) emissions are observed at higher concentrations under 365 nm UV lamp. These materials for the first time show yellow and orange emission from drop cast film of N-GQDs under 365 nm UV-light while the parent powder gives orange emission. The variety of emission colours that could be made simply by controlling the degree of aggregation presents exciting possibilities in a range of applications such as sensing, bioimaging, solar harvesting and forensic science.
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Closing both the carbon and nitrogen loops is a critical venture to support the establishment of the circular, net‐zero carbon economy. Although single atom catalysts (SACs) have gained interest for ...the electrochemical reduction reactions of both carbon dioxide (CO2RR) and nitrate (NO3RR), the structure–activity relationship for Cu SAC coordination for these reactions remains unclear and should be explored such that a fundamental understanding is developed. To this end, the role of the Cu coordination structure is investigated in dictating the activity and selectivity for the CO2RR and NO3RR. In agreement with the density functional theory calculations, it is revealed that Cu‐N4 sites exhibit higher intrinsic activity toward the CO2RR, whilst both Cu‐N4 and Cu‐N4−x‐Cx sites are active toward the NO3RR. Leveraging these findings, CO2RR and NO3RR are coupled for the formation of urea on Cu SACs, revealing the importance of *COOH binding as a critical parameter determining the catalytic activity for urea production. To the best of the authors’ knowledge, this is the first report employing SACs for electrochemical urea synthesis from CO2RR and NO3RR, which achieves a Faradaic efficiency of 28% for urea production with a current density of −27 mA cm–2 at −0.9 V versus the reversible hydrogen electrode.
Tuning the coordination structure of Cu single atom catalysts is explored for the simultaneous electrochemical conversion of CO2 and NO3− to urea. Cu‐N4 sites achieve a Faradaic efficiency of 28% for urea, demonstrating the potential of single atom catalysts for zero‐carbon fertilizer production from waste carbon dioxide and nitrates.
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