Non-noble Metal Cocatalyst Research Articles

Boosting photocatalytic hydrogen evolution of covalent organic frameworks by introducing 2D conductive metal–organic frameworks as noble metal-free co-catalysts

A conductive MOF Cu3(HHTP)2 is introduced as a non-noble metal co-catalyst into a Tp-Pa-2-COF to construct an efficient hydrogen evolution system.

Expediting H 2 Evolution over MAPbI 3 with a Nonnoble Metal Cocatalyst Mo 2 C under Visible Light

Halide perovskites have been emerging as promising photocatalytic materials for H 2 evolution from water due to their outstanding photoelectric properties. However, the lack of proper surface reactive sites greatly hinders the photocatalytic potential of these fascinating compounds. Here, Mo 2 C nanoparticles have been anchored onto methylammonium lead iodide (MAPbI 3 ) as a nonnoble metal cocatalyst to promote H 2 evolution reactions. The Mo 2 C nanoparticles have opposite zeta potential with MAPbI 3 thereby electrostatically assembled onto the MAPbI 3 surface, i.e., Mo 2 C@MAPbI 3 . Our results show that the anchored Mo 2 C nanoparticles have a strong interplay with MAPbI 3 substrate so that photogenerated electrons of MAPbI 3 can be rapidly separated and transferred into Mo 2 C for further H 2 evolution reactions. Under optimal conditions, Mo 2 C@MAPbI 3 delivers exceptionally high photocatalytic performance for visible light-driven H 2 evolution that clearly outperforms pristine MAPbI 3 and Pt-deposited MAPbI 3 . An apparent quantum efficiency as high as 12.65% at 600 ± 40 nm has been attained for H 2 evolution, surpassing most of the MAPbI 3 -based photocatalyst reported. These results signify the usefulness and applicability of Mo 2 C as a new nonnoble metal-based cocatalyst in solar water splitting.

Worm-like porous and defect-structured cadmium stannate photoanodes for enhanced solar water oxidation.

The work aims to elucidate the importance of hybrid microwave annealing technology (HMA) in ultrafast fabrication of deficient cadmium stannate (Cd2SnO4) photoanodes with a worm-like porous structure and significant enhancement of solar water oxidation performance and stability. Comparison of three synthetic routes and experimental characterization revealed that relative to conventional thermal annealing (CTA) or even with extra HMA for 5 min (optimal), direct HMA for only 8 min can form cubic Cd2SnO4 thin films of unique worm-like and highly porous nanostrucures with a large interfacial surface area, high degree of phase crystallinity and high-concentration defects. The obtained results from the photoluminescence spectra and the charge efficiency measurements collaboratively verified that compared to using CTA treatment solely, the HMA treatment is effective in significantly improving charge separation, recombination and transfer processes, mainly by an over 13.5-fold increase in the bulk charge separation efficiency. Benefiting from these merits, under optimized conditions the HMA treated Cd2SnO4 film exhibited a remarkable 6-fold and 2-fold solar photocurrent enhancement compared with those of the CTA treated one and the combined CTA-HMA treated one, respectively, and an IPCE of 39% at 300 nm and 18% at 350 nm at 1.7 V versus RHE. Despite a high external bias required in this case, the study provides a simple route for synthesis of ideal Cd2SnO4 photoanodes which can be further extended to doping engineering and non-noble metal cocatalyst deposition.

Boosting photocatalytic hydrogen generation by the combination of tunable cobaloxime and covalent organic framework

Here, we have investigated the photocatalytic activities of substituted Schiff-based COFs as photosensitizes and molecular cobaloximes as non-noble metal co-catalysts for the hydrogen production from water under visible light irradiation. The steric and electronic properties of the functional group at the backbone of COFs, and cobaloximes, have a pronounced effect on the photocatalytic performance of the photocatalytic system. We established that the methyl-substituted COF (COF-AD1) as a photosensitizer, chloro (p-N,N-dimethylpyridine) cobaloxime (Co-2) as co-catalyst and triethanolamine (TEOA) sacrificial electron donor form a highly active photocatalytic system which exhibited a record hydrogen production rate of 7072 μmolg−1h−1 with a quantum efficiency of 51.4%, TOF of 35.6, TON of 462.4 for 20 h in a 4:1 acetonitrile/water mixture.

Non-noble metal-based cocatalysts for photocatalytic CO2 reduction

Cocatalysts loading is an effective strategy to boost photocatalytic CO2 reduction reaction (CO2RR). The cocatalysts based on non-noble metal compounds have an obvious advantage in balancing the cost and efficiency in the scale-up application. The anions in non-noble metal cocatalysts have a distinctive influence on the photocatalytic CO2RR. This review focuses on the impact of different anions in non-noble metal compounds, including oxide-, sulphide-, phosphide-, carbide- and nitride-based cocatalysts. These materials have been demonstrated to improve the charge carrier separation, light harvesting, CO2 adsorption ability and act as active sites for reduction reactions. The recent progresses of non-noble metal-based cocatalysts for photocatalytic CO2RR, together with possible challenges and opportunities have been discussed.

Fe atom clusters embedded N-doped graphene decorated with ultrathin mesoporous carbon nitride nanosheets for high efficient photocatalytic performance

Atomic-level dispersed non-noble metal co-catalyst offers high potential for improving photocatalytic performance. Herein, Fe atom clusters embedded N-doped graphene (Fe-NG) stacked ultrathin mesoporous carbon nitride nanosheets (MCNS) by layer and layer that have been successfully constructed. The Fe-NG as co-catalyst can promote the effective migration of photogenerated electrons on the surface of MCNS nanosheets, thus effectively separate photogenerated carriers. Moreover, the metal atom clusters sites can absorb more reactants, which is conducive to the promotion of photocatalytic reaction. The photocatalytic activity of these composites was tested under visible light irradiation with the indissoluble antibiotics, endocrine disruptors and dyes as the target pollutants. When the mass ratios of Fe are about 0.15 wt.%, the Fe-NG/MCNS exhibited the optimum photocatalytic performance. The intermediates of various pollutants produced during the photodegradation reaction and corresponding possible degradation pathway were in-depth analyzed with mass spectrometry spectra. The ESR analysis indicated that the •O2− and •OH were the main active species for the photocatalytic degradation. A possible mechanism of Fe-NG for the enhancement of visible light performance was proposed. Meanwhile, the Fe-NG/MCNS composite shows promising application for the photo-oxidative degradation of environmental contaminants.

A 3D flower-like WC with large capacitance as efficient co-catalyst in photocatalytic H2 evolution

Non-noble metal co-catalysts can promote photo-excited charge separation of semiconductor and act as active sites for proton catalytic H2 evolution. However, how to judge which function non-noble metal co-catalyst has is not clear. Here, we reported a 3D flower-like WC (WC–F) which shows outstanding activity (24502 μmol/h/g) on CdS in photocatalytic H2 evolution. WC–F has the largest specific capacitance (12.07 F/g), which contributes to the largest electron storage capability. The integration of noble metal Pd and WC tests demonstrated WC–F has the largest proton reduction catalysis ability. Significantly, composite co-catalyst Pd/WC–F on CdS shows slightly higher (1.16 times) activity than WC–F/CdS, which means most of photoexcited electrons on WC–F have been consumed and reaction with protons to produce hydrogen. Thus, two judgement methods for both charges storage and protons catalysis were put forward.

Unveiling the role of Mn-Cd-S solid solution and MnS in MnxCd1-xS photocatalysts and decorating with CoP nanoplates for enhanced photocatalytic H2 evolution

A series of MnxCd1-xS (0 < x < 1, marked as MCS-x) photocatalysts were synthesized by a facile hydrothermal method. The Mn-Cd-S solid solution and impurity phase of α-MnS would coexist in the as-prepared products once x ≥ 0.3. Among these photocatalysts, the MCS-0.5 sample exhibited the highest photocatalytic H2 evolution rate of 5.540 mmol‧g−1‧h−1 with the lactic acid as sacrificial reagent, which may be due to the joint action of the formation of Mn-Cd-S solid solution promoting conduction band potential to enhance the reduction ability and MnS as the recombination center of photogenerated electron-hole pairs. Moreover, the photocatalytic H2 evolution performance of MCS-0.5 sample was further significantly improved on coupling with CoP nanoplates as the cocatalysts, and the optimal loading content was 5 wt% with a H2 evolution rate of 42.95 mmol‧g−1‧h−1, which was nearly 7.75 times higher than that of bare MCS-0.5 and even exceeded that of 1 wt% Pt/MCS-0.5. It could be found from the results of multiple characterization technologies that the excellent photocatalytic H2 evolution activity of CoP/MCS-0.5 composites might be probably attributed to the more efficient transfer and separation of photogenerated charge carriers at the interface between CoP and MCS-x, and more active sites provided by the CoP nanoplates. This current work would clarify the role of Mn-Cd-S solid solution and impurity phase of MnS in the MCS-x samples during the photocatalytic reaction, and reveal that CoP nanosheets might replace Pt as an effective and non-noble metal cocatalyst for the photocatalytic H2 evolution.

A ternary calabash model photocatalyst (Pd/MoP)/CdS for enhancing H2 evolution under visible light irradiation

Noble metal and non-noble metal co-catalysts have their own advantages for improving photocatalytic hydrogen evolution. Here, we report a new composite co-catalyst (Pd/MoP) and a ternary photocatalyst (Pd/MoP)/CdS for hydrogen evolution. The optimum photocatalytic hydrogen evolution of (Pd/MoP)/CdS reaches 943 μmol/h, which is 2.1 times of MoP/CdS and 4.4 times of Pd/CdS. Transient photocurrent responses, photoluminescence spectroscopies, and surface photovoltage spectroscopies demonstrated the combination of (Pd/MoP) makes high-efficiency of charge separation on CdS. Galvanostatic charge/discharge and cyclic voltammetry tests revealed MoP mainly serves as a reservoir to store photo-excited electrons from CdS. Electrochemical impedance spectra and linear sweep voltammetry measures revealed Pd mainly acts as active sites for hydrogen evolution. Most importantly, the functions of each part of ternary photocatalyst for hydrogen evolution have been clarified, and a ternary calabash model photocatalyst for hydrogen evolution is put forward.

Photocatalytic H2O2 production using Ti3C2 MXene as a non-noble metal cocatalyst

Photocatalytic H2O2 production by O2 reduction is an environmental-friendly process for solar light conversion to chemical energy. In this work, Ti3C2 MXene was used as a non-noble metal cocatalyst to load on P25 as Ti3C2/TiO2 (TC/TO) photocatalysts for photocatalytic H2O2 synthesis. A H2O2 formation rate (179.7 μmol L−1 h−1) of the optimized 10 %-TC/TO composite was obtained to be over 21 folds as high as that of P25 under UV light. Radical quenching experiments and superoxide radical detection confirmed the superoxide radical as the primary intermediate, suggesting the O2 reduction in two-step single-electron indirect reaction. The higher activity of TC/TO can be attributed to the functions of Ti3C2 MXene in accelerating the separation and transfer of photogenerated electron-hole pairs, suppressing their recombination, and blocking the surface TiOOH formation. This work proves the promising roles of Ti3C2 MXene in the photocatalytic reaction and further expands their new applications in photocatalysis.

Synergistic enhancement of photocatalytic H2 production by Ni decorated 2D bubble-like carbon nitride

In this paper, a novel 2D bubble-like g-C3N4 (B–CN) with a highly porous and crosslinked structure is successfully synthesized via a cost-effective bottom-up process. The as-prepared B–CN photocatalyst delivers a considerably expanded specific surface area and increased active sites. Moreover, the 2D bubble-like structure can afford shortened diffusion paths for both photogenerated charge carriers and reactants. As a result, the photocatalytic H2 evolution rate of B–CN reached 268.9 μmol g−1 h−1, over 5 times more than that of bulk C3N4. The Ni ions were further deposited on B–CN as a cocatalyst to enhance the photocatalytic activity. Benefit from the synergy of 2D bubble-like structure and Ni species cocatalyst, recombination of photoinduced charges was greatly inhibited and the hydrogen evolution reaction (HER) was significantly accelerated. The resulted catalyst achieved a dramatically high H2 evolution rate of 1291 μmol g−1 h−1. This work provides an alternative way to synthesize novel porous carbon nitride together with non-noble metal cocatalysts toward enhanced photocatalytic activity for H2 production.

Noble-metal-free Mo2C co-catalsyt modified perovskite oxide nanosheet photocatalysts with enhanced hydrogen evolution performance

Developing low cost and highly efficient catalysts for photocatalytic hydrogen (H2) evolution reaction holds significant function in water splitting. The co-catalysts load on semiconductor can promote the rapid separation and migration of photon-generated carriers, active interfacial reaction and suppress photocorrosion. Herein, we report the synthesis of Mo2C nanoparticles (NPs) decorated K+Ca2Nb3O10− nanosheets (K+CNO− NSs) heterojunction photocatalyst, where the Mo2C is used as a co-catalyst. The optimal Mo2C/K+CNO− sample with a Mo2C loading amount of 3 wt% yields an enhanced H2 production rate of 686.5 μmol g‒1, which is about 8.8 times higher than that of bare K+CNO‒ NSs (78.1 μmol g‒1). The enhanced photocatalytic activity might be ascribed to the faster photoinduced electrons transfer due to the ultrathin structure of K+CNO− NSs and effective charge carrier separation derived from the abundant contact heterointerfaces between K+CNO− NSs and Mo2C NPs. This study provides a guidance to construct efficient non-noble metal co-catalyst for photocatalytic H2 evolution from water splitting.

Hierarchical fabrication of hollow Co2P nanocages coated with ZnIn2S4 thin layer: Highly efficient noble-metal-free photocatalyst for hydrogen evolution

The directional synthesis of transition metal phosphides was considered to be an effective strategy to solve the overdependence of noble metals on photocatalytic hydrogen evolution (PHE) reactions. Inspiringly, this work reported a facile method for constructing hollow Co2P nanocages (Co2P NCGs) that derived from ZIF-67 by calcining and phosphiding procedure in nitrogen atmosphere to act as non-noble metal cocatalysts. Followed with further coating thin-layered ZnIn2S4 (ZIS) on the surface of Co2P NCGs through a hydrothermal reaction, the hierarchical robust Co2P/ZnIn2S4 nanocages (Co2P/ZIS NCGs) were then delicately fabricated as efficient photocatalysts for PHE reactions. The uniquely hollow structure of Co2P NCGs largely diffused the photogenerated chargers that induced from ZIS and the closely interfacial contact significantly promoted the separation and transfer of electrons from ZIS to Co2P according to density functional theory (DFT) calculation, synergistically resulting in an efficient hydrogen generation performance. PHE results showed that an efficient H2 evolution rate of 7.93 mmol/g/h over 10% Co2P/ZIS NCGs was achieved, about 10 times higher than that of pristine ZnIn2S4. More importantly, the hierarchically hollow Co2P/ZIS NCGs exhibited ascendant PHE activity in comparison with that of 1% noble metal (Pt, Au, Ag) loaded ZnIn2S4 with superior sustainability, all indicating the efficient and stable photocatalysts of Co2P/ZIS NCGs for PHE reactions.

A NiS co-catalyst decorated Zn3In2S6/g-C3N4 type-II ball-flower-like nanosphere heterojunction for efficient photocatalytic hydrogen production.

Promoting the separation of photogenerated electron-hole pairs and enhancing the charge carrier transfer are critical in photocatalysis. In our work, a ball-flower-like NiS/Zn3In2S6/g-C3N4 photocatalyst fabricated by a hydrothermal method exhibited superior performance for photocatalytic water splitting. The optimized 2.0% NiS/Zn3In2S6/g-C3N4 rivaled noble metal based Pt/g-C3N4 and showed an apparent quantum efficiency (AQE) of 24.3% at 420 nm, with a H2 yield of 4.135 mmol g-1 h-1, which was 30.4 and 9.51 times that of pure g-C3N4 and binary Zn3In2S6/g-C3N4 composites, respectively. The experimental and characterization results suggested that the heterojunction formed between Zn3In2S6/g-C3N4 and the decorating NiS co-catalyst cooperatively suppressed the electron-hole recombination and facilitated the charge carrier transfer, thus resulting in significant improvement of the H2 evolution performance. Moreover, the increased specific surface area and the enhanced visible-light absorption also contributed to superior water splitting performance. The prepared ternary catalytic system with the heterojunction and non-noble metal co-catalyst has great potential as an alternative to noble metals for achieving cost-efficient water splitting systems.

Nickel hydroxide as a non-noble metal co-catalyst decorated on Cd0.5Zn0.5S solid solution for enhanced hydrogen evolution

The study of non-noble metal photocatalysts provides practical significance for hydrogen evolution applications. Herein, new Cd0.5Zn0.5S/Ni(OH)2 catalysts were fabricated through simple hydrothermal and precipitation methods. The photocatalytic performance of the Cd0.5Zn0.5S/Ni(OH)2 composites under visible light was significantly improved, which was attributed to the wider visible light absorption range and less recombination of electron–hole pairs. The composite with a Ni(OH)2 content of 10% showed the best hydrogen evolution rate of 46.6 mmol g−1 h−1, which was almost 9 times higher than that of pristine Cd0.5Zn0.5S. The severe photo-corrosion of Cd0.5Zn0.5S was greatly improved, and the Cd0.5Zn0.5S/Ni(OH)2 composite exhibited a very high hydrogen evolution rate after three repeated tests. The excellent photocatalytic performance was due to the non-noble metal Ni(OH)2 co-catalyst. The excited electrons were transferred to the co-catalyst, which reduced electron–hole recombination. Moreover, the co-catalyst offered more sites for photocatalytic reactions. This study researched the mechanism of a co-catalyst composite, providing new possibilities for non-noble metal photocatalysts.

A solid-state glucose sensor based on Cu and Fe–doped carbon nitride

Functional nanomaterials find numerous applications in electrochemical biosensors and lab-on-a-chip devices, such as the glucose sensors used by diabetic patients. In this work, polymeric carbon nitride (g-C3N4) −which mimicks peroxidases behavior− was used, in combination with 3,3′,5,5′-tetramethylbenzidine (TMB) −a redox indicator−, to detect glucose in a quantitative way. The utilization of two non-noble metal co-catalysts, Fe(III) and Cu(II), embedded in the polymer structure by adsorption (Cu(II)–Fe(III)-g-C3N4), considerably increased the sensitivity towards glucose as compared to that of pristine g-C3N4. TMB and glucose oxidase (GOx) were also adsorbed on the catalyst, resulting in a solid-state composite that changed its color from yellow to green when exposed to a solution containing glucose. The UV–Vis monitoring of the intensity of the band at 675 nm, associated with oxidized TMB, showed that the response of the Cu(II)–Fe(III)-g-C3N4 system was faster than that of the one based on pristine g-C3N4. This behavior was further confirmed by electron spin resonance (ESR) spectroscopy. Moreover, ESR experiments conducted with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) evidenced that the Cu(II)–Fe(III)-g-C3N4 catalyst was able to produce about twice as many radicals as pristine g-C3N4. The proposed composite material may hold promise as a solid substrate for glucose sensing, given that concentration levels in the low ppb range can be detected by UV–Vis diffuse reflectance spectroscopy and concentrations above 100 ppm (μM) can be easily detected by the naked eye.

Selenium-enriched amorphous NiSe1+x nanoclusters as a highly efficient cocatalyst for photocatalytic H2 evolution

Exploiting and fabricating of novel non-noble metal cocatalysts with abundant active sites is highly required to boost the photocatalytic performance. Herein, selenium-enriched amorphous NiSe1+x nanoclusters (a-NiSe1+x) as a novel cocatalyst were rationally integrated with the TiO2 to greatly boost its hydrogen-generation rate via a simple photoinduced deposition route. It was interesting to find that in comparison with the crystalline nickel selenide (c-NiSe), the a-NiSe1+x evidently displayed more unsaturated active Se atoms because of its highly irregular arrangement structure and small particle size (0.5–2 nm). Photocatalytic results revealed that the a-NiSe1+x nanoclusters could significantly improve the hydrogen-production activity of TiO2 (4095.3 μmol h−1 g−1, AQE = 19.6%), which is higher than that of pristine TiO2 and c-NiSe/TiO2. The outstanding performance of a-NiSe1+x/TiO2 can be attributed to the synergism of facilitated photoelectron transfer from TiO2 to a-NiSe1+x cocatalyst and excellent H2-production active site of Se atoms, which was well revealed by density functional theory (DFT) calculations and in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) measurement. Based on the above results, an enriched Se-mediated mechanism is raised for the boosted H2-generation rate of a-NiSe1+x/TiO2. Moreover, the present a-NiSe1+x can also be used as the general cocatalyst for typical g-C3N4 and CdS photocatalysts. Considering the gentle preparation, low-cost and admirable activity, the a-NiSe1+x cocatalyst would have tremendousprospects for the fabrication of advanced photocatalytic materials.

Mesoporous black TiO2 phase junction@Ni nanosheets: A highly integrated photocatalyst system

Solar fuels production by using TiO2 nanomaterials has attracted much attention to overcome the energy and environmental crisis. However, it is a big challenge to utilize the visible light, promote charge separation and surface reaction, and efficiently recover nanosized TiO2 photocatalysts without secondary contamination. Here, Ni nanosheets as the non-noble metal co-catalysts are coated on the surface of mesoporous black TiO2 phase junction microspheres (Ni/b–TiO2) for highly efficient H2 evolution. The black TiO2 phase junction core can efficiently harvest the visible light and greatly facilitate the charge transfer. The Ni nanosheet shell can not only serve as a highly efficient collaborative co-catalyst to promote the separation and transfer of photogenerated charge carriers, but also enhance the visible light absorption and improve the utilization ratio of sunlight. The obtained Ni/b–TiO2 exhibits a high hydrogen evolution rate of 166.2 µmol h-1 g-1 under simulated sunlight, which is much higher than that of pristine mesoporous black TiO2 microspheres (80.5 μmol h-1 g-1). More importantly, the obtained photocatalysts can be easily separated through magnetic separation. Such a structure design may provide new insights for fabricating low-cost bifunctional photocatalysts with high-performance.

Facile synthesis of flower-like Bi2WO6/C3N4/CNT ternary composite with enhanced photoactivity: influencing factors and mechanism

Carbon nanotube (CNT)-bridged Z-scheme Bi2WO6/C3N4 ternary heterojunctions (BCT) were prepared through a two-step hydrothermal method. Field emission scanning electron microscope and transmission electron microscope images reveal the flower-like structures of prepared samples. The modification of C3N4 and CNT leads to an improved specific surface area without affecting the morphology of Bi2WO6. Optical characterizations demonstrate an improved visible light absorption for the BCT sample compared to the pure Bi2WO6 and other binary Bi2WO6/C3N4, Bi2WO6/CNT composites. Moreover, the formation of intimate ternary heterointerface (identified by HRTEM images) effectively facilitates the interfacial carrier separation and reduces the recombination of electron–hole pairs, as indicated by a series of electrochemical characterizations. The prepared BCT3 photocatalyst (incorporated with 5% of C3N4 and 1.67% of CNT) posses 0.0304 min−1 of ciprofloxacin photodegradation rate, which is a superior value than related Bi2WO6 and C3N4-based composite photocatalysts. The work functions, electronic structure and charge density difference were calculated by employing density functional theory method. The results suggest that the photogenerated electrons would transfer from Bi2WO6 to C3N4, bridging by the CNT with great conductivity and suitable work function. This charge transfer pathway corresponds to the formation of Z-scheme mechanism in prepared BCT composites, which is also supported by the trapping experiments and electron spin resonance analysis. We anticipate that the present work will be helpful for constructing highly efficient ternary Z-scheme photocatalysts by coupling a small amount of CNT as a non-noble metal cocatalyst. 3D Flower-like Bi2WO6/C3N4/CNT Z-scheme ternary composite was successfully synthesized and utilized as high-performance photocatalyst for degrading a wide range of organic pollutants.

Fabrication of a novel Ni3N/Ni4N heterojunction as a non-noble metal co-catalyst to boost the H2 evolution efficiency of Zn0.5Cd0.5S

NixN/Zn0.5Cd0.5S composites displayed better photocatalytic hydrogen production from water in comparison with pristine Zn0.5Cd0.5S (ZCS), as well as Pt/ZCS and Ni3N/ZCS.