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.
It is highly profitable to transform glycerol - the main by-product from biodiesel production to high value-added chemicals. In this work, we develop a photoelectrochemical system based on nanoporous ...BiVO
for selective oxidation of glycerol to 1,3-dihydroxyacetone - one of the most valuable derivatives of glycerol. Under AM 1.5G front illumination (100 mW cm
) in an acidic medium (pH = 2) without adscititious oxidant, the nanoporous BiVO
photoanode achieves a glycerol oxidation photocurrent density of 3.7 mA cm
at a potential of 1.2 V versus RHE with 51% 1,3-dihydroxyacetone selectivity, equivalent to a production rate of 200 mmol of 1,3-dihydroxyacetone per m
of illumination area in one hour.
Nitrogen‐doped carbon materials are proposed as promising electrocatalysts for the carbon dioxide reduction reaction (CRR), which is essential for renewable energy conversion and environmental ...remediation. Unfortunately, the unclear cognition on the CRR active site (or sites) hinders further development of high‐performance electrocatalysts. Herein, a series of 3D nitrogen‐doped graphene nanoribbon networks (N‐GRW) with tunable nitrogen dopants are designed to unravel the site‐dependent CRR activity/selectivity. The N‐GRW catalyst exhibits superior CO2 electrochemical reduction activity, reaching a specific current of 15.4 A gcatalyst−1 with CO Faradaic efficiency of 87.6% at a mild overpotential of 0.49 V. Based on X‐ray photoelectron spectroscopy measurements, it is experimentally demonstrated that the pyridinic N site in N‐GRW serves as the active site for CRR. In addition, the Gibbs free energy calculated by density functional theory further illustrates the pyridinic N as a more favorable site for the CO2 adsorption, *COOH formation, and *CO removal in CO2 reduction.
A 3D nitrogen‐doped graphene nanoribbon network is constructed by the chemical pyrolysis with high CO2 electrochemical reduction performance. The pyridinic N site is proved to be the active site by experimental and density functional theory calculations.
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.
A good electrochemical performance for a multistep electron transfer reaction calls for low thermodynamic energy barrier, fast kinetics, and abundance of surface reactive intermediates. While ...physical and spectral characterizations fail to obtain most of these details because of interference from the electrolyte and dynamic surface structures under reaction conditions, electrochemical measurements instead are able to provide the most direct information. A thermodynamic-kinetic model was developed in our previous work, which showed great capability to extract the adsorption energies of reactive intermediates through the Tafel plot without considering the exact structures of catalysts in the oxygen evolution reaction (OER). In this work, a more adaptive model in combination with probing the methanol oxidation reaction was developed. This approach offers the following advantages: From the aspect of thermodynamics, an experimentally rationalized adsorption profile could be obtained without the requirement to know the scaling factors of reactive intermediates. From the aspect of surface structure, the potential induced change of intermediates’ coverage in the reaction could be described with high sensitivity. From the aspect of kinetics, multiple Tafel slopes in a single Tafel plot could be explained by potential induced variation in intermediates’ coverage and activation energy in the rate-determining step (RDS). A volcano relation between the symmetry factor and adsorption energy was also discerned and discussed, showing the strong correlation between thermodynamics and kinetics. Our model offers a promising analyzing tool by providing essential information on the electrochemical interface and both thermodynamic and kinetic properties of catalysts, which are important for the design of next-generation high-performance catalysts for multistep electrochemical reactions.
The electrochemical oxygen reduction reaction in acidic media offers an attractive route for direct hydrogen peroxide (H2O2) generation and on-site applications. Unfortunately there is still a lack ...of cost-effective electrocatalysts with high catalytic performance. Here, we theoretically designed and experimentally demonstrated that a cobalt single-atom catalyst (Co SAC) anchored in nitrogen-doped graphene, with optimized adsorption energy of the *OOH intermediate, exhibited a high H2O2 production rate, which even slightly outperformed the state-of-the-art noble-metal-based electrocatalysts. The kinetic current of H2O2 production over Co SAC could reach 1 mA/cmdisk2 at 0.6 V versus reversible hydrogen electrode in 0.1 M HClO4 with H2O2 faraday efficiency > 90%, and these performance measures could be sustained for 10 h without decay. Further kinetic analysis and operando X-ray absorption study combined with density functional theory (DFT) calculation demonstrated that the nitrogen-coordinated single Co atom was the active site and the reaction was rate-limited by the first electron transfer step.
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•Single-atom catalysts (SACs) for H2O2 production were theoretically designed•Cobalt SAC exhibited the highest activity and selectivity for H2O2 production•In situ XAS tracked the dynamic process of the CoN4 active sites•Kinetic analysis identified the rate-determining step of the reaction
Hydrogen peroxide is a valuable chemical with extensive applications, but the current industrial production method is energy-intensive and generates substantial waste. The electrochemical oxygen reduction reaction in acidic media offers an attractive route for direct hydrogen peroxide generation and on-site applications. Unfortunately, there is still a lack of cost-effective electrocatalysts with high catalytic performance. Here, by combining theoretical calculations and experimental methods, we demonstrate that an atomically dispersed cobalt anchored in nitrogen-doped carbon can function as a highly active and selective electrocatalyst for direct hydrogen peroxide synthesis. This cobalt single-atom catalyst combines the advantages of both homogeneous catalysts of cobalt macrocycles (well-defined active sites) and heterogeneous metal-nitrogen-carbon catalysts (high catalytic performance) together, showing promising application in electrosynthesis device.
By combining theoretical and experimental methods, Gao et al. systematically studied the relationship between the structure of transition metal (Mn, Fe, Co, Ni, and Cu) single-atom catalyst anchored in nitrogen-doped graphene and the catalytic performance of hydrogen peroxide (H2O2) synthesis via electrochemical two-electron oxygen reduction reaction (ORR) (2e− ORR). The thus designed Co single-atom catalyst can function as a highly active and selective catalyst for H2O2 synthesis and even slightly outperforms state-of-the-art noble-metal-based electrocatalysts in acidic media.
The ability to suppress the recombination of the photoinduced charges is the key prerequisite for an excellent photocatalyst, which has attracted extensive and continuous interest in the field of ...photocatalysis. Herein, we presented a convenient strategy for the one-step selective synthesis of ultrathin BiOBr nanosheets with atomic thickness through a simple solvothermal method. These ultrathin BiOBr nanosheets not only show high exposure percentage of active (001) facets but also have an optimized band structure, which synergistically facilitates the electron-hole pair separation to realize significantly promoted visible-light photocatalytic activity. Our results provide a new avenue and direction for the design of photocatalysts with high visible-light photocatalytic performance.
Ultrathin BiOBr nanosheets with atomic thickness were successfully synthesized through a simple solvothermal method realizing significantly promoted visible-light photocatalytic activity.
The lack of model single-atom catalysts (SACs) and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the designed model ...single-Fe-atom catalysts with well-controlled microenvironments, we have explored the exact structure of catalytic centers and provided insights into a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the developed operando57Fe Mössbauer spectroscopy. In combination with theoretical studies, the N-FeN4C10 moiety is evidenced as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via capturing the peroxido (∗O2−) and hydroxyl (∗OH−) intermediates under in situ ORR conditions. We anticipate that the integration of operando techniques and SACs in this work shall shed some light on the electronic-level insight into the catalytic centers and underlying reaction mechanism.
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•Single-Fe-atom material with controlled microenvironment as efficient ORR catalyst•Operando57Fe Mössbauer spectroscopy developed for the characterization of SACs in ORR•Evidence for electronic and structural dynamics of single-Fe-atom moieties in ORR
Single-atom catalysts (SACs) build a conceptual bridge between homo- and heterogeneous catalysis. However, the lack of model SACs and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the newly designed model single-Fe-atom catalysts, we explored the exact structure of catalytic centers and provided a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the newly developed operando57Fe Mössbauer spectroscopy. The potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ∗O2− and ∗OH− intermediates and further supported by theoretical calculations. These results provide a proof of concept for the integration of operando techniques and SACs, which may direct the way toward the electronic-level insight into the catalytic centers and reaction mechanism.
Operando Mössbauer spectroscopy was developed for in situ monitoring the evolution of catalytic centers in single-Fe-atom catalyst under practical oxygen reduction reaction conditions. Combining with operando Raman and X-ray absorption spectroscopies, the potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ∗O2− and ∗OH− intermediates and further supported by theoretical calculations.
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