Abstract
Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN
4
site usually exhibits an ...unsatisfactory ORR activity due to its poor O
2
adsorption and activation. Here, we report an axial Fe–O coordination induced electronic localization strategy to improve its O
2
adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe–O coordination evokes the electronic localization among the axial direction of O–FeN
4
sites to enhance O
2
adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe–O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O
2
adsorption and activation with an ultralow Tafel slope of 27.5 mV dec
−1
and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.
Abstract
Atomically dispersed transition metals on carbon-based aromatic substrates are an emerging class of electrocatalysts for the electroreduction of CO
2
. However, electron delocalization of ...the metal site with the carbon support via d-π conjugation strongly hinders CO
2
activation at the active metal centers. Herein, we introduce a strategy to attenuate the d-π conjugation at single Ni atomic sites by functionalizing the support with cyano moieties. In situ attenuated total reflection infrared spectroscopy and theoretical calculations demonstrate that this strategy increases the electron density around the metal centers and facilitates CO
2
activation. As a result, for the electroreduction of CO
2
to CO in aqueous KHCO
3
electrolyte, the cyano-modified catalyst exhibits a turnover frequency of ~22,000 per hour at −1.178 V versus the reversible hydrogen electrode (RHE) and maintains a Faradaic efficiency (FE) above 90% even with a CO
2
concentration of only 30% in an H-type cell. In a flow cell under pure CO
2
at −0.93 V versus RHE the cyano-modified catalyst enables a current density of −300 mA/cm
2
with a FE above 90%.
The photoreduction of CO2 to hydrocarbon products has attracted much attention because it provides an avenue to directly synthesize value‐added carbon‐based fuels and feedstocks using solar energy. ...Among various photocatalysts, graphitic carbon nitride (g‐C3N4) has emerged as an attractive metal‐free visible‐light photocatalyst due to its advantages of earth‐abundance, nontoxicity, and stability. Unfortunately, its photocatalytic efficiency is seriously limited by charge carriers′ ready recombination and their low reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to be an efficient way to improve the charge transfer and reaction efficiency. Here, boron (B) is doped into the large cavity between adjacent tri‐s‐triazine units via coordination with two‐coordinated N atoms. Theoretical calculations prove that the new electron excitation from N (2px, 2py) to B (2px, 2py) with the same orbital direction in B‐doped g‐C3N4 is much easier than N (2px, 2py) to C 2pz in pure g‐C3N4, and improves the charge transfer and localization, and thus the reaction dynamics. Moreover, B atoms doping changes the adsorption of CO (intermediate), and can act as active sites for CH4 production. As a result, the optimal sample of 1%B/g‐C3N4 exhibits better selectivity for CH4 with ≈32 times higher yield than that of pure g‐C3N4.
Graphitic carbon nitride (g‐C3N4) exhibits unsatisfactory photocatalytic CO2 reduction activity due to its low charge transfer and reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to improve the charge transfer and reaction efficiency. In this work, B atoms are doped into g‐C3N4 for improving charge transfer and localization, and boosting the photocatalytic activity.
Excessive consumption of fossil fuels gives rise to the increasing emission of carbon dioxide (CO2) in the atmosphere and furthers the ecocrisis. Electrochemical CO2 reduction (ECR) has both ...functions of dwindling greenhouse gas concentration and converting it into valuable products. Due to the intrinsic chemical inertness of CO2 molecules, the study on efficient and low‐cost catalysts has attracted much attention. Recently isolated atoms, dispersed in stable support, play an important role in decreasing energy barriers of intermediate steps and obtaining target products with high activity and selectivity for ECR. The effective regulation of central atoms or coordination environment is significant to realize the desired performances of ECR with a high efficiency and selectivity. Hence, a comprehensive summary about strategies for improving the performance of ECR on single atom catalysts (SACs) is necessary. Herein, the SACs on various supports are introduced, the methods to design stable SACs are discussed, and the strategies for tuning the performance of ECR on SACs are summarized. The localized environment manipulation is widely used for high‐performance SACs design, including regulating central atoms and coordination environment. Finally, the perspectives are discussed to shed light on the rational design of intriguing SACs for ECR.
The performance of single atom catalysts (SACs) in carbon dioxide (CO2) electroreduction is closely related to the central atoms and its coordination environment. Strategies which include regulating the central atoms, coordination atoms, coordination number, and diatomic strategies are successfully developed to enhance the performance of SACs in CO2 reduction reaction.
The reaction interface which governs the electrocatalytic behavior is notoriously hard to understand due to inadequate regulatory and detection methods. By using on-chip microdevices, we employ ...variable back-gate voltages to generate molecular polarization and thus fine-tune the concentration of hydronium ions (H
3
O
+
) in electrochemical double layers for efficient hydrogen evolution. Taking C
60
/ MoS
2
heterojunction as a prototype, electrical tests reveal that the back-gate promotes the charge transfer from C
60
to MoS
2
, leading to the polarization of C
60
.
In situ
photoluminescence spectra verify that the polarized C
60
can attract H
3
O
+
to accumulate in the vicinity of MoS
2
in the external electric field. Profiting from the back-gated H
3
O
+
enrichment, the hydrogen evolution current is increased by five times at −0.45 V
RHE
when a 1.5-V back-gate voltage is applied. The insight into the reaction interface from manipulation to detection can facilitate diverse catalytic reactions.
Single-atom photocatalysts, due to their high catalysis activity, selectivity and stability, become a hotspot in the field of photocatalysis. Graphitic carbon nitride (g-C 3N 4) is known as both a ...good support for single atoms and a star photocatalyst. Developing g-C 3N 4-based single-atom photocatalysts exhibits great potential in improving the photocatalytic performance. In this review, we summarize the recent progress in g-C 3N 4-based single-atom photocatalysts, mainly including preparation strategies, characterizations, and their photocatalytic applications. The significant roles of single atoms and catalysis mechanism in g-C 3N 4-based single-atom photocatalysts are analyzed. At last, the challenges and perspectives for exploring high-efficient g-C 3N 4-based single-atom photocatalysts are presented.
Electrochemical production of hydrogen peroxide (H2O2) through two‐electron (2 e−) oxygen reduction reaction (ORR) is an on‐site and clean route. Oxygen‐doped carbon materials with high ORR activity ...and H2O2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen‐doped carbon nanosheet (OCNS900) catalyst for 2 e− ORR. The OCNS900 exhibits outstanding 2 e− ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g−1 at 0.75 V (vs. RHE) and H2O2 production rate of 770 mmol g−1 h−1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C−OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e− ORR, which were corroborated by theoretical calculations.
The oxygen‐doped carbon nanosheet (OCNS900) has been demonstrated as highly effective catalyst for electrosynthesizing hydrogen peroxide with mass activity of 14.5 A g−1 at 0.75 V (vs. RHE) and H2O2 production rate of 770 mmol g−1 h−1 in a flow cell. Chemical titration and DFT calculations were used to decipher the high activity for hydrogen peroxide production; the C=O groups are identified as the most active sites.
Atomically dispersed transition metal sites have been extensively studied for CO2 electroreduction reaction (CO2RR) to CO due to their robust CO2 activation ability. However, the strong hybridization ...between directionally localized d orbits and CO vastly limits CO desorption and thus the activities of atomically dispersed transition metal sites. In contrast, s‐block metal sites possess nondirectionally delocalized 3s orbits and hence weak CO adsorption ability, providing a promising way to solve the suffered CO desorption issue. Herein, we constructed atomically dispersed magnesium atoms embedded in graphitic carbon nitride (Mg‐C3N4) through a facile heat treatment for CO2RR. Theoretical calculations show that the CO desorption on Mg sites is easier than that on Fe and Co sites. This theoretical prediction is demonstrated by experimental CO temperature program desorption and in situ attenuated total reflection infrared spectroscopy. As a result, Mg‐C3N4 exhibits a high turnover frequency of ≈18 000 per hour in H‐cell and a large current density of −300 mA cm−2 in flow cell, under a high CO Faradaic efficiency ≥90 % in KHCO3 electrolyte. This work sheds a new light on s‐block metal sites for efficient CO2RR to CO.
Atomically dispersed magnesium atoms embedded in graphitized C3N4 (Mg‐C3N4) show weak CO adsorption because of nondirectionally delocalized Mg 3 s orbit. Mg‐C3N4 exhibits a high turnover frequency (TOF) of ≈18 000 hour−1 under a CO Faradaic efficiency ≥90 %. Furthermore, the flow cell fabricated with Mg‐C3N4 reaches a large current density of −300 mA cm−2 under a CO Faradaic efficiency ≥90 %.
Ruthenium (Ru)‐based catalysts, with considerable performance and desirable cost, are becoming highly interesting candidates to replace platinum (Pt) in the alkaline hydrogen evolution reaction ...(HER). The hydrogen binding at Ru sites (Ru−H) is an important factor limiting the HER activity. Herein, density functional theory (DFT) simulations show that the essence of Ru−H binding energy is the strong interaction between the 4dz2
orbital of Ru and the 1s orbital of H. The charge transfer between Ru sites and substrates (Co and Ni) causes the appropriate downward shift of the 4dz2
‐band center of Ru, which results in a Gibbs free energy of 0.022 eV for H* in the RuCo system, much lower than the 0.133 eV in the pure Ru system. This theoretical prediction has been experimentally confirmed using RuCo alloy‐nanosheets (RuCo ANSs). They were prepared via a fast co‐precipitation method followed with a mild electrochemical reduction. Structure characterizations reveal that the Ru atoms are embedded into the Co substrate as isolated active sites with a planar symmetric and Z‐direction asymmetric coordination structure, obtaining an optimal 4dz2
modulated electronic structure. Hydrogen sensor and temperature program desorption (TPD) tests demonstrate the enhanced Ru−H interactions in RuCo ANSs compared to those in pure Ru nanoparticles. As a result, the RuCo ANSs reach an ultra‐low overpotential of 10 mV at 10 mA cm−2 and a Tafel slope of 20.6 mV dec−1 in 1 M KOH, outperforming that of the commercial Pt/C. This holistic work provides a new insight to promote alkaline HER by optimizing the metal‐H binding energy of active sites.
Optimizing Ru−H adsorption/desorption efficiency, via adjusting the Ru 4dz2
orbital in RuCo alloy‐nanosheets, enables highly promoted alkaline hydrogen evolution reaction. This optimized adsorption/desorption efficiency is demonstrated by the hydrogen sensor and temperature programmed desorption experiments. The RuCo alloy‐nanosheets possess a record low overpotential of 10 mV at 10 mA cm−2, superior to the commercial Pt/C and Ru/C.
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