One-step hydrothermal synthesis of three-dimensional nitrogen-doped reduced graphene oxide hydrogels anchored PtPd alloyed nanoparticles for ethylene glycol oxidation and hydrogen evolution reactions

Discovery and biochemical characterization of thermostable glycerol oxidases

Alditol oxidases are promising tools for the biocatalytic oxidation of glycerol to more valuable chemicals. By integrating in silico bioprospecting with cell-free protein synthesis and activity screening, an effective pipeline was developed to rapidly identify enzymes that are active on glycerol. Three thermostable alditol oxidases from Actinobacteria Bacterium, Streptomyces thermoviolaceus, and Thermostaphylospora chromogena active on glycerol were discovered. The characterization of these three flavoenzymes demonstrated their glycerol oxidation activities, preference for alkaline conditions, and excellent thermostabilities with melting temperatures higher than 75 °C. Structural elucidation of the alditol oxidase from Actinobacteria Bacterium highlighted a constellation of side chains that engage the substrate through several hydrogen bonds, a histidine residue covalently bound to the FAD prosthetic group, and a tunnel leading to the active site. Upon computational simulations of substrate binding, a double mutant targeting a residue pair at the tunnel entrance was created and found to display an improved thermal stability and catalytic efficiency for glycerol oxidation. The hereby described alditol oxidases form a valuable panel of oxidative biocatalysts that can perform regioselective oxidation of glycerol and other polyols. KEY POINTS: • Rapid pipeline designed to identify putative oxidases • Biochemical and structural characterization of alditol oxidases • Glycerol oxidation to more valuable derivatives.

Alkali Etching of Porous PdCoZn Nanosheets for Boosting C-C Bond Cleavage of Ethylene Glycol Oxidation

Pd-based electrocatalysts are the most effective catalysts for ethylene glycol oxidation reaction (EGOR), while the disadvantages of poor stability, low resistance to neutrophilic, and low catalytic activity seriously hamper the development of direct ethylene glycol fuel cells (DEGFCs). In this work, defect-riched PdCoZn nanosheets (D-PdCoZn NSs) with ultrathin 2D NSs and porous structures are fabricated through the solvothermal and alkali etching processes. Benefiting from the presence of defects and ultrathin 2D structures, D-PdCoZn NSs demonstrate excellent electrocatalytic activity and good durability against EGOR in alkaline media. The mass activity and specific activity of D-PdCoZn NSs for EGOR are 9.5 A mg-1 and 15.7 mA cm-2 , respectively, which are higher than that of PdCoZn NSs, PdCo NSs, and Pd black. The D-PdCoZn NSs still maintain satisfactory mass activity after long-term durability tests. Meanwhile, in situ IR spectroscopy demonstrates that the presence of defects attenuated the adsorption of intermediates, which improves the selectivity of the C1 pathway with excellent anti-CO poisoning performance. This work not only provides an effective synthetic strategy for the preparation of Pd-based nanomaterials with defective structures but also indicates significant guidance for optimum C1 pathway selectivity of ethylene glycol and other challenging chemical transformations.

Integrated Catalyst-Substrate Electrodes for Electrochemical Water Splitting: A Review on Dimensional Engineering Strategy

Water splitting (or, water electrolysis) is considered as a promising approach to produce green hydrogen and relieve the ever-increasing energy consumption as well as the accompanied environmental impact. Development of high-efficiency, low-cost practical water-splitting systems demands elegant design and fabrication of catalyst-loaded electrodes with both high activity and long-life time. To this end, dimensional engineering strategies, which effectively tune the microstructure and activity of electrodes as well as the electrochemical kinetics, play an important role and have been extensively reported over the past years. Here, a type of most investigated electrode configurations is reviewed, combining particulate catalysts with 3D porous substrates (aerogels, metal foams, hydrogels, etc.), which offer special advantages in the field of water splitting. It is analyzed the design principles, structural and interfacial characteristics, and performance of particle-3D substrate electrode systems including overpotential, cycle life, and the underlying mechanism toward improved catalytic properties. In particular, it is also categorized the catalysts as different dimensional particles, and show the importance of building hybrid composite electrodes by dimensional control and engineering. Finally, present challenges and possible research directions toward low-cost high-efficiency water splitting and hydrogen production is discussed.

One-Stage Process of Reduction, Fluorination, and Doping with Nitrogen of Graphene Oxide Films

The possibility of chemical modification of a graphene oxide film deposited on a Si/SiO2 substrate during a one-stage hydrothermal process in the presence of fluorine ions and reducing agents, such as ascorbic acid or hydrazine, is shown. The proposed technique makes it possible to obtain reduced fluorinated graphene nitride oxide (RGOFN) in the form of a thin film with a controlled composition of functional groups by changing the type and concentration of the reducing agent and then transferring the obtained films to any substrate. XPS and IR spectroscopy of the obtained films revealed controlled changes in the structure and composition of graphene oxide associated with the removal of oxygen groups and the incorporation of fluorine ions as well as the reduction of conjugated double bonds and the controlled incorporation of nitrogen into thin RGOFN films. The current-voltage characteristics of the fabricated RGOFN structures showed that their electrical properties are well controlled by doping with nitrogen during the proposed one-stage process.

Facile Synthesis of Multifunctional Ni(OH)2 -Supported Core-Shell Ni@Pd Nanocomposites for the Electro-Oxidation of Small Organic Molecules

In the domain of proton exchange membrane fuel cells (PEMFCs), the development of efficient and durable catalysts for the electro-oxidation of small organic molecules, especially of alcohols (methanol, ethanol, ethylene glycol, et al.) has always been a hot topic. A large number of related electrocatalysts with splendid performance have been designed and synthesized till now, while the preparation processes of most of them are demanding on experimental operations and conditions. Herein, we put forward a facile and handy method for the preparation of multifunctional Ni(OH)2 -supported core-shell Ni@Pd nanocomposites (Ni(OH)2 /Ni@Pd NCs) with the assistance of galvanic replacement reaction (GRR) at room temperature and ambient pressure. As expected, the Ni(OH)2 substrate can prevent the aggregation of core-shell (CS) Ni@Pd nanoparticles (NPs) and inhibit the formation of COads and further prevent Pd from being poisoned. The synergistic effect between CS Ni@Pd NPs and Ni(OH)2 substrate and the electronic effect between Pd shell and Ni core contribute to the outstanding electrocatalytic performance for methanol, ethanol, and ethylene glycol oxidation in alkaline condition. This study provides a succinct method for the design and preparation of efficient Pd-based electrocatalysts for alcohol electro-oxidation.

N-doped graphene aerogel cathode with internal aeration for enhanced degradation of p-nitrophenol by electro-Fenton process

A columnar N-doped graphene aerogel (NGA) was successfully fabricated by one-step hydrothermal synthesis using L-hydroxyproline as reductant, N-doping, and swelling agent, and it was used as the cathode with internal aeration mode for the electro-Fenton degradation of p-nitrophenol. Owing to the stable solid-liquid-gas three-phase interface, more active defects, and modulated nitrogen dopants, the NGA cathode exhibited enhanced electrocatalytic activity. H₂O₂ could be continuously electro-generated via a two-electron oxygen reduction, and the yield of H₂O₂ was 153.3 mg·L^-1·h^-1 with the low electric energy consumption of 15.3 kWh kg^-1. Simultaneously, the NGA cathode had better charge transfer capability with N-doping, which was conducive to the conversion of Fe³⁺/Fe²⁺. Under the optimal condition, nearly 100% removal of p-nitrophenol and 84% removal of TOC were obtained within 60 and 120 min, respectively. The NGA cathode also presented good stability and versatile applicability in different water matrices. Therefore, the NGA is a cost-effective cathode material in electro-Fenton system with adequate activity and reuse stabilization.

Green application of trimetallic nickel-cobalt-molybdenum nanocomposites on 3D graphene oxide as a powerful electrocatalyst for hydrogen evolution reaction

In-situ designing of multiple metals electrocatalysts with high active sites and performance is the main challenge for hydrogen evolution reaction (HER). So in this work, 3D-rGO was easily obtained from 2D-graphene by a simple one-step hydrothermal method to create the interspace sites and active surface area. The Ni-Co-Mo tri-metallic@3D-rGO was synthesized and fully characterized by different techniques, e.g., FT-IR, XRD, Raman, FE-SEM, TEM, EDS, mapping, ICP-OES, AFM, voltammetry, and electrochemical impedance spectroscopy. According to the FE-SEM and TEM images, the Ni-Co-Mo tri-metallic@3D-rGO has a crumpled-formed structure. The as-prepared nanocomposite has high HER performance with a low potential of -0.11 (vs. RHE) to deliver 10 mA cm^-2 and Tafel slope of 68 mV dec^-1 for Pt and -0.25 V (vs. RHE) to deliver 10 mA cm^-2 and Tafel slope of 110 mV dec^-1 for graphite counter electrode. Furthermore, the 3D structure illustrates high long-term durability in the HER process for 1000 continuous cycles and 12 h operation at -0.42 V (vs. RHE) for Pt and graphite counter electrode. It's noticeable HER performance has the synergetic effect between 3D-rGO and tri-metallic structure with high porosity and electrical conductivity, enhancing HER kinetic.

A review on advances in green treatment of glycerol waste with a focus on electro-oxidation pathway

Over the past decades, research efforts are being devoted into utilizing the biomass waste as a major source of green energy to maintain the economic, environmental, and social sustainability. Specifically, there is an emerging consensus on the significance of glycerol (an underutilised waste from biodiesel industry) as a cheap, non-toxic, and renewable source for valuable chemicals synthesis. There are numerous methods enacted to convert this glycerol waste to tartronic acid, mesoxalic acid, glyceraldehyde, dihydroxyacetone, oxalic acid and so on. Among these, the green electro-oxidation technique is one of the techniques that possesses potential for industrial application due to advantages such as non-toxicity process, fast response, and lower energy consumption. The current review covers the general understanding on commonly used techniques for alcohol (C₁ & C₂) conversion, with a specific insight on glycerol (C₃) electro-oxidation (GOR). Since catalysts are the backbone of chemical reaction, they are responsible for the overall economy prospect of any processes. To this end, a comprehensive review on catalysts, which include noble metals, non-noble metals, and non-metals anchored over various supports are incorporated in this review. Moreover, a fundamental insight into the development of future electrocatalysts for glycerol oxidation along with products analysis is also presented.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

A highly sensitive strain sensor based on a silica@polyaniline core-shell particle reinforced hydrogel with excellent flexibility, stretchability, toughness and conductivity

Hydrogel-based flexible strain sensors for personal health monitoring and human-machine interaction have attracted wide interest among researchers. In this paper, hydrophobic association and nanocomposite conductive hydrogels were successfully prepared by introducing polyaniline coated silica (SiO2@PANI) core-shell particles into an acrylamide-lauryl methacrylate (P(AM/LMA)) copolymer matrix. The hydrophobic interaction between the SiO2@PANI core-shell particles and the hydrophobic LMA in the P(AM/LMA) chains induced the hydrogels with outstanding mechanical properties. Furthermore, the polyaniline on the SiO2 surface and the inorganic salt formed a conductive network, which synergistically enhanced the conductivity of the hydrogels. The obtained hydrogels integrate high tensile strength (1398 kPa), ultra-stretchability (>1000%), wonderful strain sensitivity (gauge factor = 10.407 at 100-1100% strain), quick response (300 ms), and excellent durability (>300 cycles) due to the hydrophobic association and nanocomposite effect. The prepared SiO2@PANI-P(AM/LMA) hydrogel shows high stress sensitivity to detect human movements and displays a broad application prospect in flexible strain-sensor field.

The Effects of Hydrophobicity and Textural Properties on Hexamethyldisiloxane Adsorption in Reduced Graphene Oxide Aerogels

To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas.

Synthesis of raspberry-like antimony-platinum (SbPt) nanoparticles as highly active electrocatalysts for hydrogen evolution reaction

Binary transition metals can facilitate the hydrogen evolution reaction (HER) through the synergistic integration of different electrochemical properties. To determine binary transition metals that are highly active, Greely et al. conducted a simulation of 256 different binary transition metals. They demonstrated that BiPt, PtRu, AsPt, SbPt, BiRh, RhRe, PtRe, AsRu, IrRu, RhRu, IrRe, and PtRh could be used as efficient electrocatalysts for HER. However, only few of them are synthesized and used as electrocatalysts. In this work, we report the synthesis of the raspberry-like antimony-platinum (SbPt) nanoparticles (NPs) via a colloidal nanocrystal synthesis. These NPs exhibited efficient activity with a low overpotential of 27 mV to reach 10 mA cm^-2 in acidic media. We conducted long-term durability test for 90,000 s under an applied voltage of 0.5 V (vs. RHE) and cycling tests of over 10,000 cycles under an applied voltage of 0.1 to -0.5 V (vs. RHE). The high activity exhibited by the raspberry-like SbPt NPs may be due to the following reasons: (1) the raspberry-like SbPt NPs exhibited versatile active exposed (110), (100), (101), and (012) facets as efficient HER catalysts, and (2) as confirmed by both the density functional theory (DFT) simulation and experimental results, the presence of Sb 3d subsurface broadened the Pt surface d-band, which caused synergistic effects on water splitting. In summary, synthesis of the new colloidal raspberry-like SbPt NPs is essential to elucidate the fundamental properties of the nanomaterial and nanostructure design. This study could facilitate the development of Pt-group materials that can be used as HER catalysts.

Investigation of polymer-derived Si-(B)-C-N ceramic/reduced graphene oxide composite systems as active catalysts towards the hydrogen evolution reaction

Hydrogen Evolution Reaction (HER) is an attractive technology for chemical conversion of energy. Replacement of platinum with inexpensive and stable electrocatalysts remains a major bottleneck hampering large-scale hydrogen production by using clean and renewable energy sources. Here, we report electrocatalytically active and ultra-stable Polymer-Derived Ceramics towards HER. We successfully prepared ultrathin silicon and carbon (Si–C) based ceramic systems supported on electrically conducting 2D reduced graphene oxide (rGO) nanosheets with promising HER activity by varying the nature and the composition of the ceramic with the inclusion of nitrogen, boron and oxygen. Our results suggest that oxygen-enriched Si-B-C-N/rGO composites (O-SiBCN/rGO) display the strongest catalytic activity leading to an onset potential and a Tafel slope of − 340 mV and ~ 120 mV dec⁻¹ respectively. O-SiBCN/rGO electrodes display stability over 170 h with minimal increase of 14% of the overpotential compared to ~ 1700% for commercial platinum nanoparticles. Our study provides new insights on the performance of ceramics as affordable and robust HER catalysts calling for further exploration of the electrocatalytic activity of such unconventional materials.

Tiny Ir doping of sub-one-nanometer PtMn nanowires: highly active and stable catalysts for alcohol electrooxidation

One-dimensional (1D) Pt-based nanowires (NWs) materials serve as efficient catalysts for alcohol electrocatalysis. However, precisely tailoring their size towards sub-one-nanometer scale has been verified as an effective method for enhancing electrocatalytic properties, which is rarely studied. In this work, we developed a one-pot simple yet efficient method for synthesizing a kind of sub-one-nanometer tiny Ir-doped PtMn NWs. The prepared PtMnIr NWs have an ultrathin structure with a mean diameter of around only 0.97 nm (about 3-5 atomic thickness), which display large surface areas and promote superficial Pt atom utilization. With the robust tiny Ir incorporation, the composition-optimized Pt74Mn21Ir5 NWs showed enhanced mass activity, which was 1.51 and 1.53 times higher than those of non-Ir-doped Pt79Mn21 NWs for acidic ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). Moreover, benefiting from the atom-level ultrathin size and well-tuned ligand effect from Ir to PtMn, the EOR/MOR mass activities of sub-nanometric Pt74Mn21Ir5 NWs were 3.99- and 3.98-fold higher than those of Pt/C catalysts. More importantly, after successive EOR and MOR CV tests, the Ir-doped PtMn NWs still maintained 85.6% and 73.4% of the initial mass activity, which were much better than those of Pt79Mn21 NWs, Pt NWs, and Pt/C catalysts. This work could be extended to engineering other advanced materials with super sub-one-nanometer structure, which is beneficial for largely improving the catalytic performance.

Efficient polyalcohol oxidation electrocatalysts enabled by PtM (M = Fe, Co, and Ni) nanocubes surrounded by (200) crystal facets

Due to the high-density (200) crystal planes and abundant active sites, cubic platinum nanomaterials have become outstanding electrocatalysts in promoting fuel cell reactions. However, because of the fact that the facet-controlled synthesis is difficult, it is still a grand challenge to synthesize a sequence of Pt-based nanocubes via a universal method. Herein, we report a general and simple eco-friendly solvothermal method to prepare (200)-enclosed PtM nanocubes. Different from the other nanomaterials, nanocubes are conducive to mass transfer. Moreover, the synergistic and electronic effects between M and Pt are profitable to improve the utilization of precious metals. We used (200)-encapsulated nanocrystals to evaluate their electrocatalytic performance towards glycerol and ethylene glycol oxidation reactions in an alkaline medium. In particular, Pt4Co nanocubes showed superior mass activities in glycerol and ethylene glycol oxidation reactions, which are 6.2- and 5.0-fold higher than those obtained for commercial Pt/C catalysts, respectively. Meanwhile, Pt4M catalysts manifested excellent stability in the endurance test, which is attributed to the alloying effect promoting the electrooxidation of intermediates. Our study provides an ideal method for the construction of Pt-based bimetallic nanocubes, which can be used for anode reactions of polyol fuel cells and beyond.

Morris M, G. Lyons M, Gun’ko YK. One Dimensional AuAg Nanostructures as Anodic Catalysts in the Ethylene Glycol Oxidation

Direct alcohol fuel cells are highly promising as efficient power sources for various mobile and portable applications. However, for the further advancement of fuel cell technology it is necessary to develop new, cost-effective Pt-free electrocatalysts that could provide efficient alcohol oxidation and also resist cross-over poisoning. Here, we report new electrocatalytic materials for ethylene glycol oxidation, which are based on AuAg linear nanostructures. We demonstrate a low temperature tunable synthesis that enables the preparation of one dimensional (1D) AuAg nanostructures ranging from nanowires to a new nano-necklace-like structure. Using a two-step method, we showed that, by aging the initial reaction mixture at various temperatures, we produced ultrathin AuAg nanowires with a diameter of 9.2 ± 2 and 3.8 ± 1.6 nm, respectively. These nanowires exhibited a high catalytic performance for the electro-oxidation of ethylene glycol with remarkable poisoning resistance. These results highlight the benefit of 1D metal alloy-based nanocatalysts for fuel cell applications and are expected to make an important contribution to the further development of fuel cell technology.

Target-Driven Cascade-Amplified Release of Loads from DNA-Gated Metal-Organic Frameworks for Electrochemical Detection of Cancer Biomarker

In this paper, a label-free and stimuli-responsive electrochemical biosensing platform was fabricated based on target-driven load release from DNA-gated metal-organic frameworks (MOFs) with cascade amplification. By using MOFs (UiO-66-NH₂) as a nanocarrier of electroactive molecules (methylene blue; MB) and the programmably assembled DNA acted as the gatekeeper, the biofunctionalized MOFs (MB@DNA/MOFs) were not only used as an amplified signal label but also worked as three-dimensional tracks for biosensing. In the presence of a target, the nicking endonuclease cleavage process was triggered, leading to the generation of two strands (S1 and S2). Both S1 and S2 act as stimuli to participate in the strand displacement reaction on the MB@DNA/MOFs, which caused the unlocking of the pore to release MB, resulting in the decrease of the signal. Using carcinoembryonic antigen (CEA) as a model target, the cascade-amplified biosensor presented good performance for CEA detection, ranging from 50 fg/mL to 10 ng/mL with a detection limit of 16 fg/mL. The stimuli-responsive DNA-gated MOF-based electrochemical platform exhibited three-dimensional biosensing tracks with rational utilization of the cascade amplification, providing an effective method for cancer biomarker detection.

Facile Synthesis Of Composition-Controllable PtPdAuTe Nanowires As Superior Electrocatalysts For Direct Methanol Fuel Cells

Multicomponent Pt-based nanowires (NWs) have attracted widespread attention as eletrocatalysts toward direct alcohol fuel cells because of their unique one-dimensional structure and high reaction dynamics. Quaternary PtPdAuTe NWs are designed via a facile template method, and NWs with a different composition are obtained by adjusting the feed ratio of metal precursors. The direct displacement reaction of metal precursors with Te NWs and the partial oxidation of Te lead to the formation of quaternary NWs. The rough surface and abundant reactive sites deriving from the rearrangement of metal atoms on the Te NWs surface endow the PtPdAuTe NWs with a superior electrocatalytic property and durability for methanol oxidation. The Pt₂₀ Pd₂₀ Au₁₀ Te₅₀ NWs display the largest mass activity and best stability among all catalysts. The preparation of PtPdAuTe NWs could provide a viable strategy for the preparation of other multicomponent NWs.