Photo/electrocatalysis of water (H2O) splitting and CO2 reduction reactions is a promising strategy to alleviate the energy crisis and excessive CO2 emissions. For the hydrogen evolution reaction ...(HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR) involved, the development of effective photo/electrocatalysts is critical to reduce the activation energy and accelerate the sluggish dynamics. Polyoxometalate (POM)‐based compounds with tunable compositions and diverse structures are emerging as unique photo/electrocatalysts for these reactions as they offer unparalleled advantages such as outstanding solution and redox stability, quasi‐semiconductor behaviour, etc. This Minireview provides a basic introduction related to photo/electrocatalytic HER, OER and CO2RR, followed by the classification of pristine POM‐based compounds toward different catalytic reactions. Recent breakthroughs in engineering POM‐based compounds as efficient photo/electrocatalysts are highlighted. Finally, the advantages, challenges, strategies and outlooks of POM‐based compounds on improving photo/electrocatalytic performance are discussed.
Polyoxometalate chemistry has shown great application potential in the field of catalysis. This Minireview outlines and discusses the advantages, recent advances, challenges, strategies and future development of POM‐based compounds as photo/electrocatalysts in hydrogen evolution reaction, oxygen evolution reaction, and CO2 reduction reaction.
Metal–covalent organic frameworks (MCOFs) have been recently received wide attention owing to the homogeneous distribution of active metal centers that are beneficial for enhancing the application ...potentials. However, metal complex based functional building blocks for MCOFs synthesis are limited. Herein, two new MCOFs (Ni‐Py‐COF and Ni‐Bn‐COF) were constructed via a novel nickel glyoximate based building block. Splendid photocatalytic activity on hydrogen evolution from water and great long‐term recyclability were achieved using these nickel glyoximate based MCOFs as photocatalysts. Excitingly, even without the addition of Pt co‐catalyst, the hydrogen evolution rates (HER) of Ni‐Py‐COF reached up to 626 μmol g−1 h−1, which is better than many porous organic polymers. This work not only expands the type of building units for MCOFs, but also provides meaningful insights for developing stable, efficient and earth‐abundant photocatalysts toward H2 generation.
To enrich the diversity of metal–covalent organic frameworks (MCOFs), two novel nickel glyoximate based MCOFs have been developed. Notably, favourable photocatalytic hydrogen evolution activities were achieved thanks to the uniformly and densely distributed Ni glyoximate functional cores on the Ni‐glyoximate‐COF skeletons.
Solar energy‐driven conversion of CO2 into fuels with H2O as a sacrificial agent is a challenging research field in photosynthesis. Herein, a series of crystalline porphyrin‐tetrathiafulvalene ...covalent organic frameworks (COFs) are synthesized and used as photocatalysts for reducing CO2 with H2O, in the absence of additional photosensitizer, sacrificial agents, and noble metal co‐catalysts. The effective photogenerated electrons transfer from tetrathiafulvalene to porphyrin by covalent bonding, resulting in the separated electrons and holes, respectively, for CO2 reduction and H2O oxidation. By adjusting the band structures of TTCOFs, TTCOF‐Zn achieved the highest photocatalytic CO production of 12.33 μmol with circa 100 % selectivity, along with H2O oxidation to O2. Furthermore, DFT calculations combined with a crystal structure model confirmed the structure–function relationship. Our work provides a new sight for designing more efficient artificial crystalline photocatalysts.
COF catalysts: A series of crystalline covalent organic frameworks (COFs) was designed and applied for CO2 photoreduction coupled with H2O photooxidation, in the absence of photosensitizers and sacrificial agents. This approach gives a more straightforward and clear understanding of the structure–function relationship of artificial photosynthesis.
Abstract
The design of highly stable, selective and efficient electrocatalysts for CO
2
reduction reaction is desirable while largely unmet. In this work, a series of precisely designed ...polyoxometalate-metalloporphyrin organic frameworks are developed. Noted that the integration of {ε-PMo
8
V
Mo
4
VI
O
40
Zn
4
} cluster and metalloporphyrin endows these polyoxometalate-metalloporphyrin organic frameworks greatly advantages in terms of electron collecting and donating, electron migration and electrocatalytic active component in the CO
2
reduction reaction. Thus-obtained catalysts finally present excellent performances and the mechanisms of catalysis processes are discussed and revealed by density functional theory calculations. Most importantly, Co-PMOF exhibits remarkable faradaic efficiency ( > 94%) over a wide potential range (−0.8 to −1.0 V). Its best faradaic efficiency can reach up to 99% (highest in reported metal-organic frameworks) and it exhibits a high turnover frequency of 1656 h
−1
and excellent catalysis stability ( > 36 h).
As one class of important functional materials, transition metal phosphides (TMPs) nanostructures show promising applications in catalysis and energy storage fields. Although great progress has been ...achieved, phase‐controlled synthesis of cobalt phosphides nanocrystals or related nanohybrids remains a challenge, and their use in overall water splitting (OWS) is not systematically studied. Herein, three kinds of cobalt phosphides nanocrystals encapsulated by P‐doped carbon (PC) and married with P‐doped graphene (PG) nanohybrids, including CoP@PC/PG, CoP‐Co2P@PC/PG, and Co2P@PC/PG, are obtained through controllable thermal conversion of presynthesized supramolecular gels that contain cobalt salt, phytic acid, and graphene oxides at proper temperature under Ar/H2 atmosphere. Among them, the mixed‐phase CoP‐Co2P@PC/PG nanohybrids manifest high electrocatalytic activity toward both hydrogen and oxygen evolution in alkaline media. Remarkably, using them as bifunctional catalysts, the fabricated CoP‐Co2P@PC/PG||CoP‐Co2P@PC/PG electrolyzer only needs a cell voltage of 1.567 V for driving OWS to reach the current density at 10 mA cm−2, superior to their pure‐phase counterparts and recently reported bifunctional catalysts based devices. Also, such a CoP‐Co2P@PC/PG||CoP‐Co2P@PC/PG device exhibits outstanding stability for OWS. This work may shed some light on optimizing TMPs nanostructures based on phase engineering, and promote their applications in OWS or other renewable energy options.
Cobalt phosphides nanocrystals encapsulated by P‐doped carbon (PC) and married with P‐doped graphene (PG) nanohybrids are fabricated for overall water splitting. The mixed‐phase CoP‐Co2P@PC/PG nanohybrids manifest high electrocatalytic activity that only needs a voltage of 1.567 V for driving water splitting to achieve 10 mA cm−2 current density, outperforming their pure‐phase counterparts and other reported bifunctional electrocatalysts.
Embedding cubane M4(OH)4 (M=Ni, Co) clusters within the matrix of metal–organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material ...type based on the pore‐space partition of the cubic primitive minimal‐surface net (MOF‐14‐type) has been realized. CTGU‐15 made from the Ni4(OH)4 cluster not only has very high BET surface area (3537 m2 g−1), but also exhibits bi‐microporous features with well‐defined micropores at 0.86 nm and 1.51 nm. Furthermore, CTGU‐15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU‐15 (1:2) made from ketjen black (KB) and CTGU‐15 exhibits an outstanding performance with a high mass specific peak current of 527 mA mg−1 and excellent peak current density (29.8 mA cm−2) at low potential (0.6 V). The isostructural cobalt structure (CTGU‐16) has also been synthesized, further expanding the application potential of this material type.
Split pores: A new 3D microporous metal–organic framework containing cubane Ni4(OH)4 clusters can serve as an electrocatalyst for the methanol oxidation reaction (MOR). The optimal hybrid material shows impressive electrocatalytic performance including a high mass specific peak current of 527 mA mg−1 and excellent peak current density (29.8 mA cm−2) at a very low potential (0.6 V).
Reported herein are two new polymorphic Co‐MOFs (CTGU‐5 and ‐6) that can be selectively crystallized into the pure 2D or 3D net using an anionic or neutral surfactant, respectively. Each polymorph ...contains a H2O molecule, but differs dramatically in its bonding to the framework, which in turn affects the crystal structure and electrocatalytic performance for hydrogen evolution reaction (HER). Both experimental and computational studies find that 2D CTGU‐5 which has coordinates water and more open access to the cobalt site has higher electrocatalytic activity than CTGU‐6 with the lattice water. The integration with co‐catalysts, such as acetylene black (AB) leads to a composite material, AB&CTGU‐5 (1:4) with very efficient HER catalytic properties among reported MOFs. It exhibits superior HER properties including a very positive onset potential of 18 mV, low Tafel slope of 45 mV dec−1, higher exchange current density of 8.6×10−4 A cm−2, and long‐term stability.
HER choice of surfactants: Two new Co‐MOFs phase‐selected by anionic and neutral surfactants exhibit differential affinity for entrapped water molecules, leading to a difference in the spatial accessibility of active metal sites. A composite material made from such Co‐MOFs shows impressive performance in electrocatalytic hydrogen evolution reaction (HER) as well as long‐term stability.
As hot topics in the chemical conversion of CO2, the photo‐/electrocatalytic reduction of CO2 and use of CO2 as a supporter for energy storage have shown great potential for the utilization of CO2. ...However, many obstacles still exist on the road to realizing highly efficient chemical CO2 conversion, such as inefficient uptake/activation of CO2 and mass transport in catalysts. Covalent organic frameworks (COFs), as a kind of porous material, have been widely explored as catalysts for the chemical conversion of CO2 owing to their unique features. In particular, COF‐based functional materials containing diverse active sites (such as single metal sites, metal nanoparticles, and metal oxides) offer great potential for realizing CO2 conversion and energy storage. This Minireview discusses recent breakthroughs in the basic knowledge, mechanisms, and pathways of chemical CO2 conversion strategies that use COF‐based functional catalysts. In addition, the challenges and prospects of COF‐based functional catalysts for the efficient utilization of CO2 are also introduced.
This Minireview discusses recent developments in the basic knowledge, mechanisms, and CO2 utilization strategies regarding the use of functional materials based on covalent‐organic frameworks (COFs) with diverse active sites as catalysts. Insight is provided into the challenges and prospects of COF‐based catalysts for the design of the next‐generation photo‐/electrocatalysts for the utilization of CO2.
A series of stable heterometallic Fe2M cluster‐based MOFs (NNU‐31‐M, M=Co, Ni, Zn) photocatalysts are presented. They can achieve the overall conversion of CO2 and H2O into HCOOH and O2 without the ...assistance of additional sacrificial agent and photosensitizer. The heterometallic cluster units and photosensitive ligands excited by visible light generate separated electrons and holes. Then, low‐valent metal M accepts electrons to reduce CO2, and high‐valent Fe uses holes to oxidize H2O. This is the first MOF photocatalyst system to finish artificial photosynthetic full reaction. It is noted that NNU‐31‐Zn exhibits the highest HCOOH yield of 26.3 μmol g−1 h−1 (selectivity of ca. 100 %). Furthermore, the DFT calculations based on crystal structures demonstrate the photocatalytic reaction mechanism. This work proposes a new strategy for how to design crystalline photocatalyst to realize artificial photosynthetic overall reaction.
A series of stable heterometallic Fe2M cluster‐based MOFs achieve the overall conversion of CO2 and H2O into HCOOH and O2 without the assistance of additional sacrificial agent and photosensitizer. A strategy is proposed to design crystalline photocatalysts to realize the overall artificial photosynthetic reaction.
In this work, we rationally designed a series of crystalline and stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs; MPc‐TFPN COF, M=Ni, Co, Zn) under the guidance of ...reticular chemistry. As a novel single‐site catalysts (SSCs), NiPc/CoPc‐TFPN COF exhibited outstanding activity and selectivity for electrocatalytic CO2 reduction (ECR; Faradaic efficiency of CO (FECO)=99.8(±1.24) %/ 96.1(±1.25) % for NiPc/CoPc‐TFPN COF). More importantly, when coupled with light, the FECO and current density (jCO) were further improved across the applied potential range (−0.6 to −1.2 V vs. RHE) compared to the dark environment for NiPc‐TFPN COF (jCO increased from 14.1 to 17.5 A g−1 at −0.9 V; FECO reached up to ca. 100 % at −0.8 to −0.9 V). Furthermore, an in‐depth mechanism study was established by density functional theory (DFT) simulation and experimental characterization. For the first time, this work explored the application of COFs as photo‐coupled electrocatalysts to improve ECR efficiency, which showed the potential of using light‐sensitive COFs in the field of electrocatalysis.
A series of stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs) were developed and applied for photo‐coupled electrocatalytic CO2 reduction. This work represents a new insight for the future rational design of light sensitive crystalline materials for CO2 reduction.
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