Expression of concern: Enhanced photocatalytic activity of g-C3N4/MnO composites for hydrogen evolution under visible light.

Expression of concern for 'Enhanced photocatalytic activity of g-C3N4/MnO composites for hydrogen evolution under visible light' by Na Mao et al., Dalton Trans., 2019, 48, 14864-14872, https://doi.org/10.1039/C9DT02748C.

Rational design of triazine-based conjugated polymers with enhanced charge separation ability for photocatalytic hydrogen evolution.

Triazine-based conjugated polymers (TCPs) are promising organic catalysts for green H2 production, since their photocatalytic performance can be easily regulated via appropriate molecular design. However, apart from weak absorption of visible light, weak charge separation and transport abilities also considerably restrict the photocatalytic performance of TCPs. Herein, we report two novel TCP photocatalysts with donor-acceptor (D-A) and donor-π-acceptor (D-π-A) structures using dibenzo[g,p]chrysene (Dc), thiophene (T), and 2,4,6-triphenyl-1,3,5-triazine (Tz) as the donor, π-spacer, and acceptor, respectively. Compared to Dc-Tz with a D-A structure, Dc-T-Tz exhibits a broader light absorption edge and more efficient charge separation and transmission due to its D-π-A structure and strong dipole effect. These properties enable Dc-T-Tz to display a prominent H2 production rate of 45.13 mmol h-1 g-1 under ultraviolet-visible (UV-Vis) light (λ > 300 nm). Therefore, Dc-T-Tz represents state-of-the-art TCP photocatalysts to date.

Towards Durable and High-Rate Rechargeable Aluminum Dual-ion Batteries via a Crosslinked Diphenylphenazine-based Conjugated Polymer Cathode.

Rechargeable aluminum battery (RAB) is expected to be a promising energy storage technique for grid-scale energy storage. However, the development of RABs is seriously plagued by the lack of suitable cathode materials. Herein, we report two p-type conjugated polymers of L-PBPz and C-PBPz with the same building blocks of diphenylphenazine but different linkage patterns of linear and crosslinked structures as the cathode materials for Al dual-ion batteries. Compared to the linear polymer skeleton in L-PBPz, the crosslinked structure endows C-PBPz with amorphous nature and low dihedral angles of the polymer chains, which severally contribute to the fast diffusion of AlCl4 - with large size and the electron transfer during the redox reaction of diphenylphenazine. As a result, C-PBPz delivers a much better rate performance than L-PBPz. The crosslinked structure also leads to a stable cyclability with over 80000 cycles for C-PBPz. Benefiting from the fast kinetics, meanwhile, the C-PBPz cathode could realize a high redox activity of 117 mAh g-1, corresponding to an areal capacity of 2.30 mAh cm-2, even under a high mass loading of 19.7 mg cm-2 and a low content of 10 wt% conductive agent. These results might boost the development of polymer cathodes for RABs.

Molecular Engineering in D-π-A-A-Type Conjugated Microporous Polymers for Boosting Photocatalytic Hydrogen Evolution.

Conjugated microporous polymer (CMP) photocatalysts with donor-π-acceptor (D-π-A) or donor-acceptor (D-A) structures have garnered great attention for solar-driven hydrogen generation because of their inherent charge separation nature and high surface area. Herein, we design a series of D-π-A-A-type CMP photocatalysts to uncover the influence of the content of the dibenzo[b,d]thiophene-S-S-dioxide (BTDO) acceptor on the photocatalytic activity. The results demonstrate that the acceptor content in the D-π-A-A-type CMP photocatalysts affects the electronic structure, the availability of reaction sites, and the separation between light-generated electrons and holes, which mainly determine the photocatalytic performance for H2 release. Benefiting from the synergy of light absorption, hydrophilicity, and active sites, the bare polymer PyT-BTDO-2 with an optimized BTDO content exhibits a high H2 production rate of 230.06 mmol h-1 g-1 under simulated sunlight, manifesting that the strategy of D-π-A-A structural design is efficacious for boosting the photocatalytic performance of CMP photocatalysts.

An efficient electron donor containing a silicon heteroatom for organic photocatalysts with high hydrogen production activity.

We report here 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene (SiDT) as an electron donor to construct a donor-acceptor type conjugated polymer (PSiDT-BTDO) photocatalyst with a narrow band gap by employing dibenzo[b,d]thiophene-S,S-dioxide as an electron acceptor. The resulting polymer PSiDT-BTDO could realize a high hydrogen evolution rate of 72.20 mmol h-1 g-1 under ultraviolet-visible light with a Pt co-catalyst, due to the enhanced hydrophilicity as well as the decreased recombination rate of photo-induced holes/electrons and the dihedral angles of the polymer chains. The high photocatalytic activity of PSiDT-BTDO reveals the promising application of the SiDT donor in designing high-performance organic photocatalysts for hydrogen evolution.

A low-cost naphthaldiimide based organic cathode for rechargeable lithium-ion batteries.

Recently, the development of cathode materials is becoming an important issue for lithium-ion batteries (LIBs). Compared with inorganic cathodes, the organic cathodes are developing rapidly, ascribing to their distinct merits in light weight, low cost, massive organic resources and high capacity. In this paper, a cost-efficiency naphthaldiimide (NDI) based derivative, 2,7-bis(2-((2-hydroxyethyl) amino) ethyl) benzo[lmn] [3,8] phenanthroline-1,3,6,8(2H, 7H)-tetraone (NDI-NHOH), was used as organic cathode in LIBs. The NDI-NHOH was synthesized easily via one-step process, and it showed very high thermal stability. Through mixing NDI-NHOH with acetylene black and polyvinylidene fluoride (weight ratio of 6:3:1) as composite cathode in lithium-metal based LIBs, the NDI-NHOH presented versatile electrochemical properties. From cyclic voltammetry (CV) test, it exhibited two reversible peaks for oxidation and reduction in the first cycle, respectively. Notably, the oxidation and reduction peaks were located at 2.54, 3.22 and 2.14, 2.32 V vs. Li+/Li, respectively. By employing NDI-NHOH as cathode, it demonstrated a specific capacity of about 80 mAh g-1 in the range of 1.5-3.5 V, where the batteries retained a capacity retention of 50% over 20 cycles. According to the LIBs study, it suggests that the NDI-NHOH-based derivative shows a potentially promising candidate as efficient organic cathode materials for high-performance metal-ions batteries.

Synthetic Control of Electronic Property and Porosity in Anthraquinone-Based Conjugated Polymer Cathodes for High-Rate and Long-Cycle-Life Na-Organic Batteries.

Redox-active carbonyl-containing compounds have received extensive attention as cathode materials for sodium-ion batteries (SIBs) because of their excellent attributes, including elemental sustainability, high theoretical capacity, diverse structures, and tunable properties. However, the storage of Na+ in most carbonyl-based cathode materials is plagued by the low capacity, unsatisfying rate performance, and short cycling life. Herein, we develop a series of anthraquinone-based conjugated polymer cathodes consisting of anthraquinone and benzene with different linking patterns. It reveals that the linkage sites on benzene ring could affect the electronic structures of the resulting polymers and thus their charge-storage capabilities. The 1,2,4,5-linkage on benzene leads to a high surface area, a narrow band gap, and the lowest unoccupied molecular orbital for the resulting polymer PBAQ-3. As a cathode for SIBs, it delivers a high capacity of around 200 mAh g-1 and excellent rate performance (105 mAh g-1 at 200 C) as well as stable cycling with a capacity retention of 95.8% after 1000 cycles at 0.05 A g-1 and 83.1% after 40000 cycles at 3 A g-1. Our findings highlight the influence of linking patterns of the building blocks on the electrochemical performance of organic electrodes.

An Efficient Electron Donor for Conjugated Microporous Polymer Photocatalysts with High Photocatalytic Hydrogen Evolution Activity.

Conjugated microporous polymers (CMPs) with donor-acceptor (D-A) molecular structure show high photocatalytic activity for hydrogen evolution due to the efficient light-induced electron/hole separation, which is mostly determined by the nature of electron donor and acceptor units. Therefore, the selection of electron donor and acceptor holds the key point to construct high performance polymer photocatalysts. Herein, two dibenzo[b,d]thiophene-S,S-dioxide (BTDO) containing CMP photocatalysts using tetraphenylethylene (TPE) or dibenzo[g,p]chrysene (DBC) as the electron donor to investigate the influence of the geometry of electron donor on the photocatalytic activity are design and synthesized. Compared with the twisted TPE donor, DBC has a planar molecular structure with extended π-conjugation, which promotes the charges transmission and light-induced electron/hole separation. As a result, the polymer DBC-BTDO produced from DBC donor shows a remarkable photocatalytic hydrogen evolution rate (HER) of 104.86 mmol h-1  g-1 under full arc light (λ > 300 nm), which is much higher than that of the polymer TPE-BTDO (1.80 mmol h-1  g-1 ), demonstrating that DBC can be an efficient electron donor for constructing D-A polymer photocatalysts with high photocatalytic activity for hydrogen evolution.

Quinone-based conjugated polymer cathodes synthesized via direct arylation for high performance Li-organic batteries.

Direct arylation cross-coupling reaction was employed to prepare quinone-based conjugated polymer cathodes, which realize a high reversible capacity of 200 mA h g-1 at 0.05 A g-1, an excellent rate capability of 111 mA h g-1 at 30 A g-1 (150C), and a stable cycling performance for more than 3000 cycles.

A Zn-S aqueous primary battery with high energy and flat discharge plateau.

We demonstrate a disposable aqueous primary battery chemistry that comprises environmentally benign materials of the sulfur cathode and Zn anode in a 1 M ZnCl2 aqueous electrolyte. The Zn-S battery shows a high energy density of 1083.3 Wh kg-1 for sulphur with a flat discharge voltage plateau around 0.7 V. When operating at a high mass loading of 8.3 mg cm-2 for sulfur in the cathode, the battery exhibits a very high areal capacity of 11.4 mA h cm-2 and areal energy of 7.7 mW h cm-2.

Boosting the Photocatalytic Hydrogen Evolution Activity for D-π-A Conjugated Microporous Polymers by Statistical Copolymerization.

Recently, great progress has been achieved in the design and preparation of conjugated organic polymer photocatalysts for hydrogen generation. However, it is still challenging to develop an organic polymer photocatalyst with high photoconversion efficiency. Rational structure design of organic polymer photocatalysts holds the key point to realize high photocatalytic performance. Herein, a series of donor-π-acceptor (D-π-A) conjugated organic copolymer photocatalysts is developed using statistical copolymerization by tuning the feed molar ratio of pyrene (donor) to dibenzothiophene-S,S-dioxide (acceptor) units. It reveals that the photocatalytic activity of the resulting copolymers is significantly dependent on the molar ratio of donor to acceptor, which efficiently changes the polymer structure and component. When the monomer feed ratio is 25:75, the random copolymer PyBS-3 of 10 mg with Pt cocatalyst shows a high hydrogen evolution rate of 1.05 mmol h-1 under UV/Vis light irradiation using ascorbic acid as the hole-scavenger, and an external quantum efficiency of 29.3% at 420 nm, which represents the state-of-the-art of organic polymer photocatalysts. This work demonstrates that statistical copolymerization is an efficient strategy to optimize the polymer structure for improving the photocatalytic activity of conjugated organic polymer catalysts.

Bifunctional Palladium Hydride Nanodendrite Electrocatalysts for Hydrogen Evolution Integrated with Formate Oxidation.

The rational design of advanced electrocatalysts and energy-saving electrolysis strategies is highly desirable for achieving high-efficiency electrochemical H2 generation yet challenging. In this work, we report highly branched Pd hydride nanodendrites (PdH-NDs) formed by a very facial solvothermal method and a succedent chemical H intercalation method in N,N-dimethylformamide. The electrocatalytic performance of PdH-NDs is experimentally and theoretically correlated with the morphology and composition, which has demonstrated substantially enhanced electrochemical activity and stability for formate oxidation reaction and hydrogen evolution reaction in alkaline electrolyte compared with Pd nanodendrites. Density functional theory calculations suggest a downshift of the Pd d-band center of PdH-NDs due to the dominant Pd-H ligand effects that weaken the binding energies of the intermediate catalytic species and toxic carbon monoxide. The asymmetric formate electrolyzer based on bifunctional PdH-ND electrocatalysts is first constructed, which only requires a low voltage of 0.54 V at 10 mA cm-2 for continuous H2 generation. This study reveals significant insights about the morphology/composition-performance relationship for palladium hydrides with bifunctional electroactivity.

Hydrophilic Conjugated Materials for Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution is viewed as a promising green strategy to utilize the inexhaustible solar energy and provide clean hydrogen fuels with zero-emission characteristic. The nature of semiconductor-based photocatalysts is the key point to achieve efficient photocatalytic hydrogen evolution. Conjugated materials have been recently emerging as a novel class of photocatalysts for hydrogen evolution and photocatalytic reactions due to their electronic properties can be well controlled via tailor-made chemical structures. Hydrophilic conjugated materials, a subgroup of conjugated materials, possess multiple advantages for photocatalytic applications, thus spurring remarkable progress on both material realm and photocatalytic applications. This minireview aims to provide a brief review of the recent developments of hydrophilic conjugated polymers/small molecules for photocatalytic applications, and special concern on the rational molecular design and their impact on photocatalytic performance will be reviewed. Perspectives on the hydrophilic conjugated materials and challenges to their applications in the photocatalytic field are also presented.

Exploiting Polythiophenyl-Triazine-Based Conjugated Microporous Polymer with Superior Lithium-Storage Performance.

Conjugated microporous polymers (CMPs) have been heralded as promising energy-storage materials with advantages such as chemical flexibility, porous structure, and environmentally friendliness. Herein, a novel conjugated microporous polymer was synthesized by integrating triazine, thiophene, and benzothiadiazole into a polymer skeleton, and the Li+ -storage performance for the as-synthesized polymer anode in Li-ion batteries (LIBs) was investigated. Benefiting from the inherent large surface area, plentiful redox-active units, and hierarchical porous structure, the polymer anode delivered a high Li+ storage capacity up to 1599 mAh g-1 at a current rate of 50 mA g-1 with an excellent rate behavior (363 mAh g-1 at 5 A g-1 ) and a long-term cyclability of 326 mAh g-1 over 1500 cycles at 5 A g-1 , implying that the newly developed polymer anode offers a great prospect for next-generation LIBs.

Realizing high hydrogen evolution activity under visible light using narrow band gap organic photocatalysts.

The design and synthesis of conjugated semiconducting polymers for photocatalytic hydrogen evolution have engendered intense recent interest. However, most reported organic polymer photocatalysts show a relatively broad band gap with weak light absorption ability in the visible light region, which commonly leads to a low photocatalytic activity under visible light. Herein, we synthesize three novel dithieno[3,2-b:2',3'-d]thiophene-S,S-dioxide (DTDO) containing conjugated polymer photocatalysts by a facile C-H arylation coupling polymerization reaction. The resulting polymers show a broad visible light absorption range up to 700 nm and a narrow band gap down to 1.81 eV due to the introduction of the DTDO unit. Benefiting from the donor-acceptor polymer structure and the high content of the DTDO unit, the three-dimensional polymer PyDTDO-3 without the addition of a Pt co-catalyst shows an attractive photocatalytic hydrogen evolution rate of 16.32 mmol h-1 g-1 under visible light irradiation, which is much higher than that of most reported organic polymer photocatalysts under visible light.

Bisulfone-Functionalized Organic Polymer Photocatalysts for High-Performance Hydrogen Evolution.

Conjugated polymers show great potential in the application of photocatalysis, particularly for the photoreduction reaction of water to generate hydrogen. Molecular structure design is a key part for building a high-performance organic photocatalyst. Herein, two bisulfone-containing conjugated polymer photocatalysts were constructed with 1D or 3D polymer structures, and the effect of polymer geometry on photocatalytic activity was studied. It was found that the linear polymer PySEO-1 exhibited increased photocatalytic performance compared with the 3D polymer network PySEO-2 because the enhanced coplanarity of the polymeric chain in PySEO-1 promoted the photogenerated charge-carrier transmission along the 1D main chain. As a result, an attractive hydrogen generation rate of 9477 µmol h-1 g-1 was obtained with PySEO-1 under broadband light irradiation. PySEO-1 also exhibited a high external quantum efficiency of 4.1 % at an incident light wavelength of 400 nm, demonstrating that the bisulfone-containing polymers are attractive as organic photocatalysts for hydrogen production.

Enhanced photocatalytic activity of g-C3N4/MnO composites for hydrogen evolution under visible light.

In this work, a range of g-C3N4/MnO composites were constructed using g-C3N4 nanosheets modified with MnO, and the photocatalytic performance for hydrogen evolution was evaluated by using these as-prepared g-C3N4/MnO composites as photocatalysts. It was found that the photocatalytic activity of the g-C3N4/MnO composites for hydrogen evolution is significantly enhanced compared with that of pristine g-C3N4 since the formation of heterojunctions between the MnO nanoparticles and g-C3N4 nanosheets through coordination covalent bonds promotes the charge carrier transfer and separation abilities of the composites. The loading mass of MnO also has a large influence on the photocatalytic activity of the g-C3N4/MnO composites. Particularly, the g-C3N4/MnO-5 composite with 5 wt% MnO shows superior photocatalytic activity with a hydrogen evolution rate of 559 µmol h-1 g-1 under visible light, which is about 9 times that of the bulky g-C3N4. These findings demonstrate that the combination of metal oxides and g-C3N4 to construct composite photocatalysts is an effective method to improve the photocatalytic performance.

Cyanogel auto-reduction induced synthesis of PdCo nanocubes on carbon nanobowls: a highly active electrocatalyst for ethanol electrooxidation.

Direct ethanol fuel cells (DEFCs) with a high conversion efficiency are quite promising candidates for energy conversion devices. Herein, we have successfully synthesized PdCo alloy nanocubes supported on carbon nanobowl (denoted as Pd2Co1/CNB) nanohybrids by using the cyanogel auto-reduction method at high temperature. The morphology, composition and structure of Pd2Co1/CNB nanohybrids are characterized in detail, revealing that PdCo nanocubes have a high alloying degree and special {110} facets. In cyclic voltammetry measurements, Pd2Co1/CNB nanohybrids show a mass activity of 1089.0 A g Pd-1 and a specific activity of 40.03 mA cm-2 for ethanol electrooxidation at peak potential, which are much higher than that of the commercial Pd/C electrocatalyst (278.2 A gPd-1 and 8.22 mA cm-2). Additionally, chronoamperometry measurements show that Pd2Co1/CNB nanohybrids have excellent durability for ethanol electrooxidation. A high alloying degree, special {110} facets and the CNB supporting material contribute to the high activity and durability of Pd2Co1/CNB nanohybrids, making them a highly promising Pt-alternative electrocatalyst for ethanol electrooxidation in DEFCs.

Conjugated Microporous Polymers with Tunable Electronic Structure for High-Performance Potassium-Ion Batteries.

Conjugated microporous polymers (CMPs) with π-conjugated skeletons show great potential as energy storage materials due to their porous structure and tunable redox nature. However, CMPs and the structure-performance relationships have not been well explored for potassium-ion batteries (KIBs). Here, we report the structure-engineered CMP anodes with tunable electronic structures for high-performance KIBs. The results demonstrate that the electronic structure of the CMPs plays an important role in enhancing potassium storage capability, including the lowest unoccupied molecular orbital (LUMO) distribution, LUMO energy level, and band gap, which can be finely tuned by synthetic control. It was revealed that the poly(pyrene- co-benzothiadiazole) (PyBT) with optimized structure delivers a high reversible capacity of 428 mAh g-1 and shows an excellent cycling stability over 500 cycles. Our findings provide a fundamental understanding in the design of CMP anode materials for high-performance potassium-organic energy storage devices.

A ZnCl2 water-in-salt electrolyte for a reversible Zn metal anode.

We report a low-cost water-in-salt electrolyte, of 30 m ZnCl2, which enables a dendrite-free Zn metal anode to possess a high coulombic efficiency (CE). In asymmetric Zn‖Zn cells with a limited mass of plated Zn as the working electrode, the ZnCl2 WiSE improves the average CE of the Zn anode to 95.4% from 73.2% in 5 m ZnCl2.