The vapochromism of the platinum( ii ) terpyridyl complex Pt(tpy)Cl(PF 6 ) ( 1 , tpy = 2,2′:6′,2′′-terpyridine) was investigated. Complex 1 was found to exist in two forms. The yellow form of 1 ...turned to red by exposing the solid to either vapor or solution of acetonitrile, accompanied by changes in luminescence spectroscopy. This process could be reversed upon the loss of acetonitrile. Complex 1 was also demonstrated to show aggregation in a diethyl ether–acetonitrile system through Pt⋯Pt and terpyridyl π–π interactions to afford the red form of 1 . Crystals of the red and yellow forms of 1 were analyzed. The red form of 1 crystallizes in the orthorhombic space group Pnma with a co-crystallized acetonitrile solvent molecule and thus is defined as 1 -MeCN, while the yellow form is found to have the previously reported non-solvated crystal structure of 1 . In 1 -MeCN, the square planar Pt(tpy)Cl + monocations stack to give an extended chain-like array of Pt atoms with a short Pt⋯Pt distance of 3.362 Å, while in 1 , there are two alternating Pt⋯Pt distances (4.032 and 3.340 Å). Time-dependent density functional theory (TDDFT) calculations demonstrated that Pt⋯Pt and terpyridyl π–π interactions play important roles in electronic absorption features of the Pt(tpy)Cl + system. Compared to dimers, the stack of three molecules of 1 with a short Pt⋯Pt distance considerably lowers the transition energy of metal–metal-to-ligand charge transfer (MMLCT), which causes a dramatic red shift in UV-vis spectroscopy.
Facile deposition of a water-splitting catalyst on low-cost electrode materials could be attractive for hydrogen production from water and solar energy conversion. Herein we describe fast ...electrodeposition of cobalt-based water oxidation catalyst （Co-WOC） on simple graphite electrode for water splitting, The deposition process is quite fast, which reaches a plateau in less than 75 min and the final ctLrrent density is -1.8 mA/cm2 under the applied potential of 1.31 V at pH --7.0. The scanning electron microscopy （SEM） study shows the formation of nanometer-sized particles （10-100 nm） on the surface of the electrode after only 2 min and micrometer-sized particles （2-5/zm） after 90 rain of electrolysis. X-ray photoelectron spectroscopy （XPS） data demonstrate the as-synthesized ex-situ catalyst mainly contains Co2＋ and Co3＋ species incorporating a substantial amount of phosphate anions. These experiments suggest that cost-efficient cobalt oxide materials on graphite exhibit alluring ability for water splitting, which might provide a novel method to fabricate low-cost devices for electrochemical energy storage.
The commercialization of fuel cells, especially for direct formic acid fuel cells (DFAFCs) and proton‐exchange membrane fuel cells (PEMFCs), is significantly restrained by the high cost, poor ...stability, and sluggish kinetics of platinum group metals (PGM) catalysts for both the anodic formic acid oxidation reaction (FAOR) and the cathodic oxygen reduction reaction (ORR). Currently, it has confronted with challenges, including exploring highly active, cost‐effective, and stable catalysts to replace PGM for DFAFCs and PEMFCs. Recently, the increasing investigation has been focused on the single‐atom catalysts (SACs) to enhance the catalytic performance owing to the maximum atom utilization and highly exposed active sites. The aim of this review is to present the recent research activities on carbon supported SACs. At the beginning of the review, metal‐based SACs supported on different carbon supports, and the typical characterization methods are introduced. Subsequently, recent advances in metal‐based SACs for FAOR and ORR catalysis are scientifically summarized. Particularly, some representative metal‐based SACs for ORR activity are further exemplified with a deeper understanding of structure‐activity relationships. Finally, the challenges and opportunities of SACs are prospected, such as the mechanism understanding and commercial applications.
A wide range of single‐atom catalysts (SACs) embedded in carbon‐based supports have attracted increasing attention for catalytic reactions due to their unique properties beyond the nanostructure counterparts. This review highlights the potential of SACs as new advanced electrocatalysts to maximize the formic acid oxidation reaction and oxygen reduction reaction catalytic activity and alleviate the use of costly platinum group metals.
Alkaline exchange membrane fuel cells (AEMFCs) have broad application prospects due to the use of low-cost, non-precious catalysts. Furthermore, a wide range of fuels, for example, carbon-neutral ...hydrogen (H
2
) and ammonia (NH
3
), can be directly used in H
2
-fueled AEMFCs and NH
3
-fueled AEM direct ammonia fuel cells (AEM-DAFCs). However, the development of the above-mentioned AEMFCs is hindered by the sluggish dynamics of the alkaline hydrogen oxidation reaction (HOR), ammonium oxidation reaction (AOR), and oxygen reduction reaction (ORR) and low efficiency catalysts for these electrode reactions. Thus, it is expected that the rational design and controlled synthesis of highly efficient, durable catalysts will enable AEMFCs to achieve comparable performance to or even a higher performance than that of proton exchange membrane fuel cells (PEMFCs), which usually require high-cost platinum group metals (PGMs). In particular, the proposed catalytic mechanism of these reactions in alkaline media is still under debate, especially of the HOR and AOR. Herein, we present an in-depth, comprehensive understanding of the alkaline HOR, AOR, and ORR based on metal catalysts, especially employing PGM-free catalysts, including the proposed mechanisms and the current development of catalysts and AEMFCs. Finally, we highlight the prevailing challenge of the mechanisms and catalysts for each reaction and outline the possible development directions for AEMFCs. We anticipate that this review will offer global scientific insights and a roadmap for the design of catalysts for alkaline electrode reactions to accelerate the further development of AEMFC technology.
We present a comprehensive understanding of the alkaline hydrogen oxidation reaction (HOR), ammonium oxidation reaction (AOR), and oxygen reduction reaction (ORR) based on metal catalysts for H
2
or NH
3
-fueled alkaline exchange membrane fuel cells.
The modulation effect has been widely investigated to tune the electronic state of single‐atomic M‐N‐C catalysts to enhance the activity of oxygen reduction reaction (ORR). However, the in‐depth ...study of modulation effect is rarely reported for the isolated dual‐atomic metal sites. Now, the catalytic activities of Fe‐N4 moiety can be enhanced by the adjacent Pt‐N4 moiety through the modulation effect, in which the Pt‐N4 acts as the modulator to tune the 3d electronic orbitals of Fe‐N4 active site and optimize ORR activity. Inspired by this principle, we design and synthesize the electrocatalyst that comprises isolated Fe‐N4/Pt‐N4 moieties dispersed in the nitrogen‐doped carbon matrix (Fe‐N4/Pt‐N4@NC) and exhibits a half‐wave potential of 0.93 V vs. RHE and negligible activity degradation (ΔE1/2=8 mV) after 10000 cycles in 0.1 M KOH. We also demonstrate that the modulation effect is not effective for optimizing the ORR performances of Co‐N4/Pt‐N4 and Mn‐N4/Pt‐N4 systems.
We have designed an efficient oxygen reduction reaction (ORR) electrocatalyst of Fe‐N4/Pt‐N4@NC with Fe‐N4 and Pt‐N4 dual atomic sites. The enhancement for the ORR activity is demonstrated by the modulation effect: Pt‐N4 plays the role in modulating the Fe‐N4 active center to optimize the ORR performance. The modulation effect is not effective for the enhancement of ORR performance in the systems of Co‐N4/Pt‐N4@NC and Mn‐N4/Pt‐N4@NC.
Developing highly active electrocatalysts for the hydrogen evolution reaction (HER) is crucial to construct an efficient water-splitting device. In this present study, a novel ternary cobalt-nickel ...phosphide nanosheet with nanowire edges on 3D nickel foam (CoNiPatNF) was first synthesized and used as an excellent cathode for the HER over a wide pH range from 0 to 14. The cathode showed high-performance catalytic activity to produce hydrogen in aqueous solution, with quite low overpotentials of only 60 mV (0.5 M H sub(2)SO sub(4), pH similar to 0.26), 120 mV (1.0 M KPi, pH similar to 7), and 155 mV (1.0 M KOH, pH similar to 14) to reach a current density of 10 mA cm super(-2). This high performance is probably due to the combination of the advantages of both one-dimensional nanowire and two-dimensional nanosheet materials, which can effectively improve the electrochemical performance for the HER. To the best of our knowledge, the present ternary CoNiP material is among the best noble-metal-free electrocatalysts for hydrogen evolution in water.
A series of nickel hydroxide-modified cadmium sulfide/reduced graphene oxide (Ni(OH)2-CdS/rGO) nanocomposites were synthesized and characterized. The photocatalytic activity of the as-prepared ...Ni(OH)2-CdS/rGO materials for hydrogen production from water under visible light irradiation (λ > 420 nm) was investigated. The results demonstrated that Ni(OH)2 is an efficient cocatalyst for photocatalytic hydrogen production and rGO can significantly enhance the rate of photocatalysis. The optimal Ni(OH)2 loading was found to be 1.0 wt %, giving a rate for hydrogen production of 4731 μmol·h–1·g–1, which is nearly 10 times higher than that of CdS/rGO photocatalyst under the same condition. This work demonstrated the synergetic effect of Ni(OH)2 and rGO to enhance catalytic activity for visible light-driven hydrogen production.
Fe−N−C catalysts with single‐atom Fe−N4 configurations are highly needed owing to the high activity for oxygen reduction reaction (ORR). However, the limited intrinsic activity and dissatisfactory ...durability have significantly restrained the practical application of proton‐exchange membrane fuel cells (PEMFCs). Here, we demonstrate that constructing adjacent metal atomic clusters (ACs) is effective in boosting the ORR performance and stability of Fe−N4 catalysts. The integration of Fe−N4 configurations with highly uniform Co4 ACs on the N‐doped carbon substrate (Co4@/Fe1@NC) is realized through a “pre‐constrained” strategy using Co4 molecular clusters and Fe(acac)3 implanted carbon precursors. The as‐developed Co4@/Fe1@NC catalyst exhibits excellent ORR activity with a half‐wave potential (E1/2) of 0.835 V vs. RHE in acidic media and a high peak power density of 840 mW cm−2 in a H2−O2 fuel cell test. First‐principles calculations further clarify the ORR catalytic mechanism on the identified Fe−N4 that modified with Co4 ACs. This work provides a viable strategy for precisely establishing atomically dispersed polymetallic centers catalysts for efficient energy‐related catalysis.
Constructing metal atomic clusters can effectively boost the oxygen reduction reaction (ORR) performance and stability of Fe−N4 on the N‐doped carbon (NC) substrate. The Co4@/Fe1@NC catalyst is realized through a “pre‐constrained” strategy using Co4 molecular clusters and Fe(acac)3 implanted carbon precursors and the obtained catalyst exhibits excellent ORR activity.
Single‐atom active‐site catalysts have attracted significant attention in the field of photocatalytic CO2 conversion. However, designing active sites for CO2 reduction and H2O oxidation ...simultaneously on a photocatalyst and combining the corresponding half‐reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single‐atom active‐site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn1Co1/CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H2O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO2 activation by increasing the bond length and bond angle of CO2 molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn1Co1/CN exhibited a CO production rate of 47 μmol g−1 h−1, which is significantly higher than that of the corresponding single‐metal active‐site photocatalyst.
Mn and Co bimetallic hetero‐single‐atoms were introduced in carbon nitride photocatalysts as redox‐active sites for CO2 conversion. The construction of a bimetallic single atom as a redox site greatly promotes the separation and transfer of charges, thereby exhibiting an excellent CO2 conversion performance.
The first realization of a tunable band‐gap in monolayer WS2(1−x)Se2x is demonstrated. The tuning of the bandgap exhibits a strong dependence of S and Se content, as proven by PL spectroscopy. ...Because of its remarkable electronic structure, monolayer WS2(1−x)Se2x exhibits novel electrochemical catalytic activity and offers long‐term electrocatalytic stability for the hydrogen evolution reaction.
