Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by ...simply calcining the mixture of graphitic carbon nitride (g‐C3N4) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g‐C3N4. The resultant boron‐doped and nitrogen‐deficient g‐C3N4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h−1 g−1, much higher than previously reported g‐C3N4. It is well evidenced that with conduction and valence band positions substantially and continuously tuned by the simultaneous introduction of boron dopants and nitrogen defects into g‐C3N4, the band structures are exceptionally modulated for both effective optical absorption in visible light and much increased driving force for water oxidation. Moreover, the engineered electronic structure creates abundant unsaturated sites and induces strong interlayer C–N interaction, leading to efficient electron excitation and accelerated charge transport. In the present work, a facile approach is successfully demonstrated to engineer the electronic structures and the band structures of g‐C3N4 with simultaneous introduction of dopants and defects for high‐performance photocatalytic oxygen evolution, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.
Boron dopants and nitrogen defects are simultaneously introduced into g‐C3N4 through a simple NaBH4 thermal treatment approach. With exceptionally modulated band structures for effective optical absorption and increased water‐oxidation driving force, as well as engineered electronic structure for efficient electron excitation and facilitated charge transport, the resultant boron‐doped and nitrogen‐deficient g‐C3N4 exhibits excellent activity for photocatalytic oxygen evolution.
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The electrosynthesis from 5‐hydroxymethylfurfural (HMF) is considered a green strategy to achieve biomass‐derived high‐value chemicals. As the molecular structure of HMF is relatively complicated, ...understanding the HMF adsorption/catalysis behavior on electrocatalysts is vital for biomass‐based electrosynthesis. The electrocatalysis behavior can be modulated by tuning the adsorption energy of the reactive molecules. In this work, the HMF adsorption behavior on spinel oxide, Co3O4 is discovered. Correspondingly, the adsorption energy of HMF on Co3O4 is successfully tuned by decorating with single‐atom Ir. It is observed that compared with bare Co3O4, single‐atom‐Ir‐loaded Co3O4 (Ir‐Co3O4) can enhance adsorption with the CC groups of HMF. The synergetic adsorption can enhance the overall conversion of HMF on electrocatalysts. With the modulated HMF adsorption, the as‐designed Ir‐Co3O4 exhibits a record performance (with an onset potential of 1.15 VRHE) for the electrosynthesis from HMF.
Single atoms of Ir are anchored on Co3O4 for efficient electro‐oxidation of 5‐hydroxymethylfurfural (HMF). It is found that an isolated Ir atom can optimize the adsorption configuration of HMF molecules on catalysts and accelerate HMF oxidation.
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Combining noble metals with nonnoble metals is an attractive strategy to balance the activity and cost of electrocatalysts. However, a guiding principle for selecting suitable nonnoble metals is ...still lacking. Herein, a thorough mechanistic study on the platform oxygen evolution reaction (OER) electrocatalyst of Ir@Co3O4 to deeply understand the synergy between Ir and Co3O4 for the boosted OER has been carried out. It is demonstrated that the pseudocapacitive feature of Co3O4 plays a key role in accumulating sufficient positive charge Q, while the Ir sites are responsible for achieving a high reaction order (β), synergistically contributing to the high OER activity of Ir@Co3O4 through the rate law equation. Specifically, Ir@Co3O4 displays a low overpotential of 280 mV at 10 mA cm−2 with a small Ir loading of 1.4 wt%. Ir@Co3O4 is further applied to Zn‐air batteries, which enables a low charging potential and thus alleviates the oxidative corrosion of the air electrode, leading to improved cycle stability of 210 h at 20 mA cm−2. This work demonstrates that anchoring active noble metal sites (for high β) on pseudocapacitive supports (for high Q) is highly favorable to the OER process, providing a clear guidance for boosting the utilization of noble metals in electrocatalysis.
Ultra‐low loading Ir (1.4 wt%) is anchored on Co3O4 for oxygen evolution reaction (OER). The pseudocapacitive Co3O4 helps accumulate the positive charge Q, while the Ir sites help achieve a high reaction order (β). Anchoring the ultra‐low loading noble catalyst on the pseudocapacitive non‐noble catalyst is a promising strategy for high‐performance low‐cost catalyst development.
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The electrooxidation of 5‐hydroxymethylfurfural (HMF) offers a promising green route to attain high‐value chemicals from biomass. The HMF electrooxidation reaction (HMFOR) is a complicated process ...involving the combined adsorption and coupling of organic molecules and OH− on the electrode surface. An in‐depth understanding of these adsorption sites and reaction processes on electrocatalysts is fundamentally important. Herein, the adsorption behavior of HMF and OH−, and the role of oxygen vacancy on Co3O4 are initially unraveled. Correspondingly, instead of the competitive adsorption of OH− and HMF on the metal sites, it is observed that the OH− can fill into oxygen vacancy (Vo) prior to couple with organic molecules through lattice oxygen oxidation reaction process, which could accelerate the rate‐determining step of the dehydrogenation of 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA) intermediates. With the modulated adsorption sites, the as‐designed Vo‐Co3O4 shows excellent activity for HMFOR with the earlier potential of 90 and 120 mV at 10 mA cm−2 in 1 m KOH and 1 m PBS solution. This work sheds insight on the catalytic mechanism of oxygen vacancy, which benefits designing a novel electrocatalysts to modulate the multi‐molecules combined adsorption behaviors.
The electrooxidation of 5‐hydroxymethylfurfural (HMFOR) process is complicated, including the HMF and OH− jointly adsorbed and coupled with each other. In this work, the role of oxygen vacancies is investigated during HMFOR. It is found that the OH− tends to fill into Vo and participate in the dehydrogenation of HMF molecules, which can improve the catalytic activity of HMFOR.
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Co‐based spinel oxides, which are of mixing valences with the presence of both Co2+ and Co3+ at different atom locations, are considered as promising catalysts for the electrochemical oxidation of ...5‐hydroxymethylfurfural (HMF). Identifying the role of each atom site in the electroxidation of HMF is critical to design the advanced electrocatalysts. In this work, we found that Co2+Td in Co3O4 is capable of chemical adsorption for acidic organic molecules, and Co3+Oh play a decisive role in HMF oxidation. Thereafter, the Cu2+ was introduced in spinel oxides to enhance the exposure degree of Co3+ and to boost acidic adsorption and thus to enhance the electrocatalytic activity for HMF electrooxidation significantly.
The exploration of optimal geometrical site in Co3O4 for electrochemical HMF oxidation by the building tetrahedral (Zn2+) and octahedral (Al3+) blocks is described. The electrochemical results demonstrate that Co3+Oh are the best geometrical sites for HMF oxidation, and the chemical adsorption for acidic organic molecules is dominated by Co2+Td. The exposure degree of Co3+ is improved by Cu2+ and thus results in a record activity.
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The selective hydrogenation of acetylene to ethylene in an ethylene‐rich gas stream is an important process in the chemical industry. Pd‐based catalysts are widely used in this reaction due to their ...excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single‐atom catalysts on nitrogen‐doped graphene (Pd1/N‐graphene) by a freeze‐drying‐assisted method is reported. The Pd1/N‐graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C2H2 with H2 in the presence of excess C2H4 under photothermal heating (UV and visible‐light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C2H4 hydrogenation. Importantly, the Pd1/N‐graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar‐driven photothermal catalyst systems based on single‐atom active sites for selective hydrogenation reactions.
Pd single‐atom catalysts on nitrogen‐doped graphene are successfully fabricated. A Pd1/N‐graphene catalyst (Pd loading of 2.3 wt%) exhibits outstanding activity and selectivity for the selective hydrogenation of acetylene in the presence of excess ethylene under photothermal or direct thermal heating at 125 °C, which is attributed to the suppression of C2H4 hydrogenation to C2H6 by Pd‐N4 surface sites.
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The activity of electrocatalysts strongly depends on the number of active sites, which can be increased by downsizing electrocatalysts. Single‐atom catalysts have attracted special attention due to ...atomic‐scale active sites. However, it is a huge challenge to obtain atomic‐scale CoOx catalysts. The Co‐based metal–organic frameworks (MOFs) own atomically dispersed Co ions, which motivates to design a possible pathway to partially on‐site transform these Co ions to active atomic‐scale CoOx species, while reserving the highly porous features of MOFs. In this work, for the first time, the targeted on‐site formation of atomic‐scale CoOx species is realized in ZIF‐67 by O2 plasma. The abundant pores in ZIF‐67 provide channels for O2 plasma to activate the Co ions in MOFs to on‐site produce atomic‐scale CoOx species, which act as the active sites to catalyze the oxygen evolution reaction with an even better activity than RuO2.
Through the efficient and mild O2‐plasma process, atomic‐scale CoOx species in a ZIF‐67 matrix are on‐site formed, which are in favor of combining with OH* to act as active sites to directly catalyze the oxygen evolution reduction with an even better activity than commercial RuO2.
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It is of essential importance to design an electrocatalyst with excellent performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting. Co3O4 has been ...developed as a highly efficient OER electrocatalyst, but it has almost no activity for HER. In a previous study, it has been demonstrated that the formation of oxygen vacancies (VO) in Co3O4 can significantly enhance the OER activity. However, the stability of VO needs to be considered, especially under the highly oxidizing conditions of the OER process. It is a big challenge to stabilize the VO in Co3O4 while reserving the excellent activity. Filling the oxygen vacancies with heteroatoms in the VO-rich Co3O4 may be a smart strategy to stabilize the VO by compensating the coordination numbers and obtain an even surprising activity due to the modification of electronic properties by heteroatoms. Herein, we successfully transformed VO-rich Co3O4 into an HER-OER electrocatalyst by filling the in situ formed VO in Co3O4 with phosphorus (P-Co3O4) by treating Co3O4 with Ar plasma in the presence of a P precursor. The relatively lower coordination numbers in VO-Co3O4 than those in pristine Co3O4 were evidenced by X-ray adsorption spectroscopy, indicating that the oxygen vacancies were created after Ar plasma etching. On the other hand, the relatively higher coordination numbers in P-Co3O4 than those in VO-Co3O4 and nearly same coordination number as that in pristine Co3O4 strongly suggest the efficient filling of P in the vacancies by treatment with Ar plasma in the presence of a P precursor. The Co–O bonds in Co3O4 consist of octahedral Co3+(Oh)–O and tetrahedral Co2+(Td)–O (Oh, octahedral coordination by six oxygen atoms and Td, tetrahedral coordination by four oxygen atoms). More Co3+(Oh)–O are broken when oxygen vacancies are formed in VO-Co3O4, and more electrons enter the octahedral Co 3d orbital than those entering the tetrahedral Co 3d orbital. Then, with the filling of P in the vacancy site, electrons are transferred out of the Co 3d states, and more Co2+(Td) than Co3+(Oh) are left in P-Co3O4. These results suggest that the favored catalytic ability of P-Co3O4 is dominated by the Co2+(Td) site. P-Co3O4 shows superior electrocatalytic activities for HER and OER (among the best non-precious metal catalysts). Owing to its superior efficiency, P-Co3O4 can directly catalyze overall water splitting with excellent performance. The theoretical calculations illustrated that the improved electrical conductivity and intermediate binding by P-filling contributed significantly to the enhanced HER and OER activity of Co3O4.
Red phosphorus is a promising photocatalyst with wide visible‐light absorption up to 700 nm, but the fast charge recombination limits its photocatalytic hydrogen evolution reaction (HER) activity. ...Now, 001‐oriented Hittorf's phosphorus (HP) nanorods were successfully grown on polymeric carbon nitride (PCN) by a chemical vapor deposition strategy. Compared with the bare PCN and HP, the optimized PCN@HP hybrid exhibited a significantly enhanced photocatalytic activity, with HER rates reaching 33.2 and 17.5 μmol h−1 from pure water under simulated solar light and visible light irradiation, respectively. It was theoretically and experimentally indicated that the strong electronic coupling between PCN and 001‐oriented HP nanorods gave rise to the enhanced visible light absorption and the greatly accelerated photoinduced electron–hole separation and transfer, which benefited the photocatalytic HER performance.
001‐oriented hexagonal‐shaped Hittorf's phosphorus (HP) nanorods with exposed {110} facets were grown on polymeric carbon nitride (PCN) for boosting photocatalytic hydrogen evolution from pure water. The enhanced visible light absorption and accelerated charge transfer efficiency through the P−N bonds and the 001‐oriented HP nanorods were crucial for the improved photocatalytic activity.
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Rational design and synthesis of hetero‐coordinated moieties at the atomic scale can significantly raise the performance of the catalyst and obtain mechanistic insight into the oxygen‐involving ...electrocatalysis. Here, a facile plasma‐photochemical strategy is applied to construct atomically coordinated Pt–Co–Se moieties in defective CoSe2 (CoSe2−x) through filling the plasma‐created Se vacancies in CoSe2−x with single Pt atomic species (CoSe2−x‐Pt) under ultraviolet irradiation. The filling of single Pt can remarkably enhance the oxygen evolution reaction (OER) activity of CoSe2. Optimal OER specific activity is achieved with a Pt content of 2.25 wt% in CoSe2−x‐Pt, exceeding that of CoSe2−x by a factor of 9. CoSe2−x‐Pt shows much better OER performance than CoSe2−x filled with single Ni and even Ru atomic species (CoSe2−x‐Ni and CoSe2−x‐Ru). Noticeably, it is general that Pt is not a good OER catalyst but Ru is; thus the design of active sites for electrocatalysis at an atomic level should follow a different intrinsic mechanism. Mechanism studies unravel that the single Pt can induce much higher electronic distribution asymmetry degree than both single Ni and Ru, and benefit the interaction between the Co sites and adsorbates (OH*, O*, and OOH*) during the OER process, leading to a better OER activity.
Atomically coordinated Pt–Co–Se moieties are generated by filling Se vacancies in defective CoSe2 with single Pt atoms (CoSe2−x‐Pt) under ultraviolet irradiation. Even though Pt is not a good oxygen evolution reaction (OER) catalyst, single Pt can induce a higher electronic distribution asymmetry degree than single Ni and Ru, and benefit the interaction between Co sites and adsorbates, endowing CoSe2−x‐Pt with much better OER performance.
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