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[Display omitted] • Dynamic Ir electronic and geometric structural change with surface adsorption. • pH-dependent oxygenate adsorption and Ir dissolution pathway. • Unfavorable adsorption coincides with distorted Ir linkage and decreased Ir valence state. The interaction between catalyst surfaces and adsorbed oxygen intermediates is critical to catalytic performance for electrochemical water oxidation to oxygen. However, the relationship between adsorption energetics and electrocatalytic activity is primarily assessed for pristine catalyst materials, which leaves much unknown about the dynamics of these properties in relationship to catalyst performance during long-term operation. In this work, we experimentally assess OH and O adsorption on Ca 2 IrO 4 nanoparticles and monitor their evolution during extensive chronoamperometry tests at highly oxidizing potentials in a range of low pH electrolytes. In situ x-ray absorption spectroscopy reveals changes for surface adsorbate energetics and local iridium structures with applied potentials. Increasingly unfavorable adsorption of OH and formation of O intermediates after long-term operation is correlated with severe metal dissolution, distorted [IrO 6 ] octahedral linkages, and a decreased average Ir valence. This work establishes connections between surface adsorption energetics, Ir structure, OER kinetics, and material stability outcomes. [ABSTRACT FROM AUTHOR]

Surface recombination at the photoanode/electrolyte junction seriously impedes photoelectrochemical (PEC) performance. Through coating of photoanodes with oxygen evolution catalysts, the photocurrent can be enhanced; however, current systems for water splitting still suffer from high recombination. We describe herein a novel charge transfer system designed with BiVO4 as a prototype. In this system, porphyrins act as an interfacial‐charge‐transfer mediator, like a volleyball setter, to efficiently suppress surface recombination through higher hole‐transfer kinetics rather than as a traditional photosensitizer. Furthermore, we found that the introduction of a "setter" can ensure a long lifetime of charge carriers at the photoanode/electrolyte interface. This simple interface charge‐modulation system exhibits increased photocurrent density from 0.68 to 4.75 mA cm−2 and provides a promising design strategy for efficient photogenerated charge separation to improve PEC performance. [ABSTRACT FROM AUTHOR]

Surface recombination at the photoanode/electrolyte junction seriously impedes photoelectrochemical (PEC) performance. Through coating of photoanodes with oxygen evolution catalysts, the photocurrent can be enhanced; however, current systems for water splitting still suffer from high recombination. We describe herein a novel charge transfer system designed with BiVO4 as a prototype. In this system, porphyrins act as an interfacial‐charge‐transfer mediator, like a volleyball setter, to efficiently suppress surface recombination through higher hole‐transfer kinetics rather than as a traditional photosensitizer. Furthermore, we found that the introduction of a "setter" can ensure a long lifetime of charge carriers at the photoanode/electrolyte interface. This simple interface charge‐modulation system exhibits increased photocurrent density from 0.68 to 4.75 mA cm−2 and provides a promising design strategy for efficient photogenerated charge separation to improve PEC performance. [ABSTRACT FROM AUTHOR]

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single‐side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2C3Tx MXene quantum dots (MQDs) and α‐Fe2O3 nanodots (FO) are anchored on the surface of ZnIn2S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S−O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high‐performance composite electrodes. [ABSTRACT FROM AUTHOR]

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single‐side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2C3Tx MXene quantum dots (MQDs) and α‐Fe2O3 nanodots (FO) are anchored on the surface of ZnIn2S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S−O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high‐performance composite electrodes. [ABSTRACT FROM AUTHOR]

Iron, nitrogen‐codoped carbon (Fe−N−C) nanocomposites have emerged as viable electrocatalysts for the oxygen reduction reaction (ORR) due to the formation of FeNxCy coordination moieties. In this study, results from first‐principles calculations show a nearly linear correlation of the energy barriers of key reaction steps with the Fe magnetic moment. Experimentally, when single Cu sites are incorporated into Fe−N−C aerogels (denoted as NCAG/Fe−Cu), the Fe centers exhibit a reduced magnetic moment and markedly enhanced ORR activity within a wide pH range of 0–14. With the NCAG/Fe−Cu nanocomposites used as the cathode catalyst in a neutral/quasi‐solid aluminum–air and alkaline/quasi‐solid zinc–air battery, both achieve a remarkable performance with an ultrahigh open‐circuit voltage of 2.00 and 1.51 V, large power density of 130 and 186 mW cm−2, and good mechanical flexibility, all markedly better than those with commercial Pt/C or Pt/C‐RuO2 catalysts at the cathode. [ABSTRACT FROM AUTHOR]

Iron, nitrogen‐codoped carbon (Fe−N−C) nanocomposites have emerged as viable electrocatalysts for the oxygen reduction reaction (ORR) due to the formation of FeNxCy coordination moieties. In this study, results from first‐principles calculations show a nearly linear correlation of the energy barriers of key reaction steps with the Fe magnetic moment. Experimentally, when single Cu sites are incorporated into Fe−N−C aerogels (denoted as NCAG/Fe−Cu), the Fe centers exhibit a reduced magnetic moment and markedly enhanced ORR activity within a wide pH range of 0–14. With the NCAG/Fe−Cu nanocomposites used as the cathode catalyst in a neutral/quasi‐solid aluminum–air and alkaline/quasi‐solid zinc–air battery, both achieve a remarkable performance with an ultrahigh open‐circuit voltage of 2.00 and 1.51 V, large power density of 130 and 186 mW cm−2, and good mechanical flexibility, all markedly better than those with commercial Pt/C or Pt/C‐RuO2 catalysts at the cathode. [ABSTRACT FROM AUTHOR]

Heteroatom‐doped carbon materials are promising electrocatalysts towards the oxygen reduction reaction (ORR). In this study, dual metals (Fe an Co) and nitrogen‐codoped porous carbon cages (CHS−FeCo) were synthesized by controlled pyrolysis of silica nanoparticle‐supported melamine‐formaldehyde resin embedded with iron and cobalt precursors, followed by acid etching. Transmission electron microscopy measurements confirmed the formation of hollow carbon cages, and the absence of metal (oxide) nanoparticles suggested atomic dispersion of the metal species within the mesoporous carbon skeletons. X‐ray photoelectron spectroscopic analysis revealed a composition of mostly carbon, oxygen, and nitrogen, with ca. 1 % metals. Electrochemically, the dual‐metal ones showed a significant enhancement of the catalytic performance towards ORR in alkaline media, as compared to samples with single or no metal dopants. This was accounted for by the synergistic interaction between the Fe and Co centers in the carbon samples, as evidenced in X‐ray absorption spectroscopic studies. Remarkably, the CHS−FeCo sample exhibited apparent resistance against KSCN poisoning, where XPS analysis revealed oxidation of KSCN and no metal‐sulfur interaction, in sharp contrast to the Fe counterpart which was easily poisoned. Results from this study suggest that the synergistic interactions between dual metal centers may be exploited for enhanced ORR performance of carbon‐based nanocomposite catalysts. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene quantum dots (NGQDs) prepared by hydrothermal treatment of citric acid and urea were used as an effective support for platinum nanoparticles synthesized by carbon monoxide reduction of Pt(IV) in water. TEM measurements showed that the platinum nanoparticles were 2.03 ± 0.43 nm in diameter, and wrapped with one layer of NGQDs, as compared to results from AFM measurements. XPS measurements confirmed the formation of metallic platinum and the incorporation of nitrogen dopants within the graphitic molecular skeleton, and the shifts of Pt 4f binding energy suggested that charge transfer from Pt to NGQDs was facilitated by the more electronegative nitrogen dopants, as compared to platinum nanoparticle supported on undoped GQDs (Pt-GQDs). Because of this, the Pt-NGQDs nanocomposites showed markedly enhanced catalytic activity towards oxygen reduction reactions in alkaline media, as compared to Pt-GQDs, with a specific activity more than three times that of commercial Pt/C. Further comparison with NGQDs-supported gold nanoparticles showed that the platinum nanoparticles, rather than the NGQDs, played a dominant role in determining the ORR activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru,N-codoped carbon aerogels by controlled pyrolysis of biomass hydrogels. • Fraction of RuN x moieties increases with increasing 1,10-phenanthroline feed. • Remarkable HER activity in a wide range of pH from 0 to 14. • High performance and stability in full water splitting. • Ru sites at the zigzag edges and nanowrinkles responsible for the HER performance. Development of cost-effective catalysts for hydrogen evolution reaction (HER) plays a significant role in scalable production of hydrogen. Herein, carbon aerogels doped with atomically isolated Ru are produced pyrolytically from biomass hydrogels and exhibit a remarkable performance in HER within a broad range of solution pH, due to the formation of abundant RuN x moieties. At the current density of 10 mA cm−2, the optimal sample (NCAG/Ru-3) exhibits an ultralow overpotential of merely −4 mV in 1.0 M KOH, −45 mV in 1.0 M phosphate buffer solution and −65 mV in 0.5 M H 2 SO 4 , with the respective mass activity 44, 16 and 6 times that of commercial Pt/C benchmark. The excellent performance is also manifested in full water splitting. Theoretical calculations suggest that the high activity arise from the RuN x sites at the zigzag edges and nanowrinkles. These results underscore the unique quality of carbon aerogel-based single atom catalysts in electrochemical energy technologies. [ABSTRACT FROM AUTHOR]

Graphene oxides with different surface charges were fabricated from carboxylated graphene oxide by chemical modification with amino- (–NH2), poly-m-aminobenzene sulfonic acid- (–NH2/–SO3H), or methoxyl- (–OCH3) terminated functional groups. The chemically functionalized graphene oxides and the carboxylated graphene oxide were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, UV-Vis spectrometry, ζ potential measurements, field emission scanning electron microscopy, and contact angle analyses. Subsequently, the resulting graphene oxides were used as substrates for culturing primary rat hippocampal neurons to investigate neurite outgrowth and branching. The morphological features of neurons that directly reflect their potential capability in synaptic transmission were characterized. The results demonstrate that the chemical properties of graphene oxide can be systematically modified by attaching different functional groups that confer known characteristics to the substrate. By manipulating the charge carried by the functionalized graphene oxides, the outgrowth and branching of neuronal processes can be controlled. Compared with neutral, zwitterionic, or negatively charged graphene oxides, positively charged graphene oxide was found to be more beneficial for neurite outgrowth and branching. The ability to chemically modify graphene oxide to control neurite outgrowth could be implemented clinically, especially in cases wherein long-term presence of outgrowth modulation is necessary. [ABSTRACT FROM AUTHOR]

Development of high-efficiency electrocatalysts for pH-universal overall water splitting is a critical step towards a sustainable hydrogen economy. Herein, graphene nanocomposites with Ru-RuO 2 Mott-Schottky heterojunctions (Ru-RuO 2 @NPC) are prepared pyrolytically and exhibit a remarkable electrocatalytic activity at pH = 0–14 towards both oxygen/hydrogen evolution reactions and overall water splitting, as compared to commercial RuO 2 and Pt/C. Ru-RuO 2 @NPC can also be used as an effective air cathode catalyst for flexible, rechargeable zinc-air batteries. Density functional theory calculations show that the formation of Ru-RuO 2 heterojunctions moderately enhances the surface charge density of metallic Ru and brings the d states closer to Fermi level, as compared to that of RuO 2 alone, leading to improved intrinsic electrocatalytic activity towards these important reactions. These results demonstrate the significance of Mott-Schottky heterojunctions in the development of high-efficiency electrocatalysts for various new energy technologies. [Display omitted] • Doped carbon nanocomposites with Ru-RuO 2 Mott-Schottky heterojunctions. • Modulation of electronic structures by interfacial charge transfer. • Bifunctional electrocatalysts for pH-universal water splitting. • Oxygen catalysts for flexible metal-air battery. [ABSTRACT FROM AUTHOR]

The supramolecular interaction between the host molecule β-cyclodextrin (β-CD) and the guest molecule adamantane is extensively applied in several disciplines. However, recent studies on the applications of this molecular recognition mainly focused on glass, silicon, and gold substrates. Few studies have explored the field of poly(dimethylsiloxane) (PDMS), an optically transparent elastomer widely used in biological microfluidic devices. In the present study, various functional group-modified adamantyl-terminated dendronized molecules were synthesized via an efficient and facile route. The binding of adamantyl-terminated dendronized molecules onto β-CD-conjugated PDMS surfaces and their reversible dissociation from PDMS surfaces through the competitive mechanism of β-CD-N3 were studied. The results showed that the dissociation is relatively slow compared with the binding, and the former process can be accelerated through exchanging the original β-CD-N3 solution with a fresh one. Afterward, more complex multilayer assemblies were constructed on PDMS surfaces using the host–guest interaction between adamantane and β-CD as well as between biotin and streptavidin. A further study on the association and dissociation of the established multilayer assemblies showed that the assembly constructed with a biotinylated monoadamantyl-terminated molecule has a reversible property, whereas that with a biotinylated triadamantyl-terminated molecule has an irreversible property. These results demonstrated that the reversible properties of the fabricated assembly can be easily modulated on the PDMS surfaces by regulating the valence of the supramolecular interaction between adamantane and β-CD. [ABSTRACT FROM AUTHOR]

Abstract: Porphyrin is able to specifically combine with phosphorus, thus a novel bifunctional sensing platform for determination of porphyrin by visual colorimetry and electrochemistry was demonstrated. A pretreated gold sheet (or electrode) with 2-mercatpoethanol (2-ME) was chemically modified by POCl3 to obtain the surface phosphate active sites. The different stages of modified electrode were characterized by electrochemical impedance spectroscopy (EIS). The 1:1 cationic sitting-atop (SAT) complex P(V)–porphyrin was formed due to the high affinity of the modified gold sheet (or electrode) towards the porphyrin, resulting in electron transfer resistance increase of the electrode surface. Meanwhile, a dramatic color changing from burgundy to dark green of porphyrin solution was observed with the naked-eye within 3s. What''s more, this was reflected by the notable change of the Soret band of porphyrin when using UV–vis. Two sensing systems provide different sensitivity for porphyrin analysis. With visual colorimetry, porphyrin can be detected at a level of 1.0×10−6 M, whereas the detection limit of porphyrin is 3.0×10−8 M using the EIS method. The practical application of the sensor to determination of pheophytin which was obtained from fresh spinach leaves has been accomplished. The results demonstrate the facility and effectivity of our introduced bifunctional biosensor for quantitative analysis of porphyrin. [Copyright &y& Elsevier]