NiFe‐based layered double hydroxides (LDHs) are among the most efficient oxygen evolution reaction (OER) catalysts in alkaline medium, but their long‐term OER stabilities are questionable. In this ...work, it is demonstrated that the layered structure makes bulk NiFe LDH intrinsically not stable in OER and the deactivation mechanism of NiFe LDH in OER is further revealed. Both operando electrochemical and structural characterizations show that the interlayer basal plane in bulk NiFe LDH contributes to the OER activity, and the slow diffusion of proton acceptors (e.g., OH−) within the NiFe LDH interlayers during OER causes dissolution of NiFe LDH and therefore decrease in OER activity with time. To improve diffusion of proton acceptors, it is proposed to delaminate NiFe LDH into atomically thin nanosheets, which is able to effectively improve OER stability of NiFe LDH especially at industrial operating conditions such as elevated operating temperatures (e.g., at 80 °C) and large current densities (e.g., at 500 mA cm−2).
The interlayer basal plane in bulk NiFe layered double hydroxide (LDH) contributes to the oxygen evolution reaction (OER) activity. Restricted diffusion of proton acceptors within the interlayers of bulk NiFe LDH causes catalyst dissolution. Exfoliating multilayered NiFe LDH into single‐layered nanosheets greatly improves the catalytic stability of NiFe LDH in alkaline OER.
Designing effective electrocatalysts for the carbon dioxide reduction reaction (CO2RR) is an appealing approach to tackling the challenges posed by rising CO2 levels and realizing a closed carbon ...cycle. However, fundamental understanding of the complicated CO2RR mechanism in CO2 electrocatalysis is still lacking because model systems are limited. We have designed a model nickel single‐atom catalyst (Ni SAC) with a uniform structure and well‐defined Ni‐N4 moiety on a conductive carbon support with which to explore the electrochemical CO2RR. Operando X‐ray absorption near‐edge structure spectroscopy, Raman spectroscopy, and near‐ambient X‐ray photoelectron spectroscopy, revealed that Ni+ in the Ni SAC was highly active for CO2 activation, and functioned as an authentic catalytically active site for the CO2RR. Furthermore, through combination with a kinetics study, the rate‐determining step of the CO2RR was determined to be *CO2−+H+→*COOH. This study tackles the four challenges faced by the CO2RR; namely, activity, selectivity, stability, and dynamics.
Ni‐che reaction: In situ reduction of nickel(II) 2,9,16,23‐tetra(amino)phthalocyanine, anchored on the surface of carbon nanotubes, yields nickel single atoms. Advanced spectroscopy of the single‐atom catalyst reveals that Ni+ is a highly active catalytic site for CO2 activation and reduction.
Heteroatom doped atomically dispersed Fe1‐NC catalysts have been found to show excellent activity toward oxygen reduction reaction (ORR). However, the origin of the enhanced activity is still ...controversial because the structure‐function relationship governing the enhancement remains elusive. Herein, sulfur(S)‐doped Fe1‐NC catalyst was obtained as a model, which displays a superior activity for ORR towards the traditional Fe‐NC materials. 57Fe Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy revealed that incorporation of S in the second coordination sphere of Fe1‐NC can induce the transition of spin polarization configuration. Operando 57Fe Mössbauer spectra definitively identified the low spin single‐Fe3+‐atom of C‐FeN4‐S moiety as the active site for ORR. Moreover, DFT calculations unveiled that lower spin state of the Fe center after the S doping promotes OH* desorption process. This work elucidates the underlying mechanisms towards S doping for enhancing ORR activity, and paves a way to investigate the function of broader heteroatom doped Fe1‐NC catalysts to offer a general guideline for spin‐state‐determined ORR.
The enhanced oxygen reduction reaction (ORR) activity of sulfur‐doped Fe‐N‐C single‐atom catalysts is studied from Fe spin‐state tuning. Operando 57Fe Mössbauer spectra monitoring further supported the low‐spin (LS) single‐Fe3+‐atom of the C‐FeN4‐S moiety as the active site for the ORR.
Rationally designing active and durable catalysts for the oxygen evolution reaction (OER) is of primary importance in water splitting. Perovskite oxides (ABO3) with versatile structures and multiple ...physicochemical properties have triggered considerable interest in the OER. The leaching of A site cations can create nanostructures and amorphous motifs on the perovskite matrix, thus facilitating the OER process. However, selectively dissolving A site cations and simultaneously obtaining more active amorphous motifs derived from the B site cations remains a great challenge. Herein, a top‐down strategy is proposed to transform bulk crystalline perovskite (LaNiO3) into a nanostructured amorphous hydroxide by FeCl3 post‐treatment, resulting in an extremely low overpotential of 189 mV at 10 mA cm−2. The top‐down‐constructed amorphous catalyst with a large surface area has dual NiFe active sites, where high‐valence Ni3+‐based edge‐sharing octahedral frameworks are surrounded by interstitial distorted Fe octahedra and contribute to the superior OER performance. This top‐down strategy provides a valid way to design novel perovskite‐derived catalysts.
An amorphous NiFe‐based catalyst (a‐LNF(t‐d)) is constructed from LaNiO3 perovskite oxide through a top‐down strategy involving FeCl3 post‐treatment, which selectively dissolves the La ions and deposits the Fe ions. The a‐LNF(t‐d) sample, with large surface area and unusual electronic/geometrical structure shows extremely high oxygen evolution reaction (OER) activity and stability.
Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pH-universal ...electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm
with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur.
Hydrogen spillover is a well-known phenomenon in heterogeneous catalysis; it involves H
cleavage on an active metal followed by the migration of dissociated H species over an 'inert' support
. ...Although catalytic hydrogenation using the spilled H species, namely, spillover hydrogenation, has long been proposed, very limited knowledge has been obtained about what kind of support structure is required to achieve spillover hydrogenation
. By dispersing Pd atoms onto Cu nanomaterials with different exposed facets, Cu(111) and Cu(100), we demonstrate in this work that while the hydrogen spillover from Pd to Cu is facet independent, the spillover hydrogenation only occurs on Pd
/Cu(100), where the hydrogen atoms spilled from Pd are readily utilized for the semi-hydrogenation of alkynes. This work thus helps to create an effective method for fabricating cost-effective nanocatalysts with an extremely low Pd loading, at the level of 50 ppm, toward the semi-hydrogenation of a broad range of alkynes with extremely high activity and selectivity.
Direct electrolysis of pH‐neutral seawater to generate hydrogen is an attractive approach for storing renewable energy. However, due to the anodic competition between the chlorine evolution and the ...oxygen evolution reaction (OER), direct seawater splitting suffers from a low current density and limited operating stability. Exploration of catalysts enabling an OER overpotential below the hypochlorite formation overpotential (≈490 mV) is critical to suppress the chloride evolution and facilitate seawater splitting. Here, a proton‐adsorption‐promoting strategy to increase the OER rate is reported, resulting in a promoted and more stable neutral seawater splitting. The best catalysts herein are strong‐proton‐adsorption (SPA) materials such as palladium‐doped cobalt oxide (Co3–xPdxO4) catalysts. These achieve an OER overpotential of 370 mV at 10 mA cm−2 in pH‐neutral simulated seawater, outperforming Co3O4 by a margin of 70 mV. Co3–xPdxO4 catalysts provide stable catalytic performance for 450 h at 200 mA cm−2 and 20 h at 1 A cm−2 in neutral seawater. Experimental studies and theoretical calculations suggest that the incorporation of SPA cations accelerates the rate‐determining water dissociation step in neutral OER pathway, and control studies rule out the provision of additional OER sites as a main factor herein.
Direct electrolysis of pH‐neutral seawater is not only a promising approach to produce clean hydrogen energy, but also of great significance to seawater desalination. Now, both the simulations and experimental characterizations illustrate that incorporating the strong‐proton‐adsorption cations into Co3O4 can increase the rate‐determining water dissociation step and achieve industrially required current density of >200 mA cm−2 in natural seawater.
The implementation of water splitting systems, powered by sustainable energy resources, appears to be an attractive strategy for producing high‐purity H2 in the absence of the release of carbon ...dioxide (CO2). However, the high cost, impractical operating conditions, and unsatisfactory efficiency and stability of conventional methods restrain their large‐scale development. Seawater covers 70% of the Earth's surface and is one of the most abundant natural resources on the planet. New research is looking into the possibility of using seawater to produce hydrogen through electrolysis and will provide remarkable insight into sustainable H2 production, if successful. Here, guided by density functional theory (DFT) calculations to predict the selectivity of gas‐evolving catalysts, a seawater‐splitting device equipped with affordable state‐of‐the‐art electrocatalysts composed of earth‐abundant elements (Fe, Co, Ni, and Mo) is demonstrated. This device shows excellent durability and specific selectivity toward the oxygen evolution reaction in seawater with near 100% Faradaic efficiency for the production of H2 and O2. Powered by a single commercial III–V triple‐junction photovoltaic cell, the integrated system achieves spontaneous and efficient generation of high‐purity H2 and O2 from seawater at neutral pH with a remarkable 17.9% solar‐to‐hydrogen efficiency.
A seawater photoelectrolysis system based on earth‐abundant catalysts is developed, which exhibits excellent durability and specific selectivity toward the oxygen evolution reaction with a remarkable 17.9% solar‐to‐hydrogen conversion efficiency.
The continuous oxidation and leachability of active sites in Ru‐based catalysts hinder practical application in proton‐exchange membrane water electrolyzers (PEMWE). Herein, robust inter‐doped ...tungsten–ruthenium oxide heterostructures (Ru–W)Ox fabricated by sequential rapid oxidation and metal thermomigration processes are proposed to enhance the activity and stability of acidic oxygen evolution reaction (OER). The introduction of high‐valent W species induces the valence oscillation of the Ru sites during OER, facilitating the cyclic transition of the active metal oxidation states and maintaining the continuous operation of the active sites. The preferential oxidation of W species and electronic gain of Ru sites in the inter‐doped heterostructure significantly stabilize RuOx on WOx substrates beyond the Pourbaix stability limit of bare RuO2. Furthermore, the asymmetric Ru–O–W active units are generated around the heterostructure interface to adsorb the oxygen intermediates synergistically, enhancing the intrinsic OER activity. Consequently, the inter‐doped (Ru–W)Ox heterostructures not only demonstrate an overpotential of 170 mV at 10 mA cm−2 and excellent stability of 300 h in acidic electrolytes but also exhibit the potential for practical applications, as evidenced by the stable operation at 0.5 A cm−2 for 300 h in PEMWE.
The robust inter‐doped (Ru–W)Ox heterostructures enhance the activity and stability of acidic oxygen evolution reaction (OER) by inducing valence oscillation and stabilizing RuOx on WOx substrates. The asymmetric Ru–O–W units synergistically adsorb oxygen intermediates, resulting in improved intrinsic activity and demonstrating potential for practical applications with low overpotential and excellent stability.
Ni‐rich layered oxides are one of the most attractive cathode materials in high‐energy‐density lithium‐ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we ...report a strong dependence of degradation pathways on the long‐range cationic disordering of Co‐free Ni‐rich Li1−m(Ni0.94Al0.06)1+mO2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near‐surface region of NA particles with very low cation disorder (NA‐LCD, m≤0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a “core–shell” structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA‐HCD, 0.06≤m≤0.15) that lead to a slow capacity decay upon cycling.
A series of Ni‐rich Li1−m(Ni0.94Al0.06)1+mO2 (NA) oxides are synthesized through tailoring the heating temperature. The NA oxides with high cation disorder experience a comparably homogeneous fatigue process upon extended cycling, while a disordered surface with lattice mismatch is gradually formed in the NA with low cation disorder (i.e. heterogeneous degradation) which results in a rapid capacity decay during the fast charge–discharge cycling.
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