Hierarchical Graphene-Based Material for Over 4.0 Wt % Physisorption Hydrogen Storage Capacity

A hierarchical graphene material composed of micropore (∼0.8 nm), mesopore (∼4 nm), and macropore (>50 nm) and with a specific surface area up to 1305 m² g^–1 is fabricated for physisorption hydrogen storage at atmospheric air pressure, showing a capacity over 4.0 wt %, which is significantly higher than reported graphene materials and all other kinds of carbon materials

Activation Enhancement of Citric Acid Cycle to Promote Bioelectrocatalytic Activity of <i>arcA</i> Knockout <i>Escherichia coli</i> Toward High-Performance Microbial Fuel Cell

The bioelectrocatalysis in microbial fuel cells (MFCs) relies on both electrochemistry and metabolism of microbes. We discovered that under MFC microaerobic condition, an <i>arcA</i> knockout mutant Escherichia coli (arcA^–) shows enhanced activation of the citric acid cycle (TCA cycle) for glycerol oxidation, as indicated by the increased key enzymes’ activity in the TCA cycle. Meanwhile, a diffusive electron mediator (hydroxyl quinone derivative) is excreted by the genetically engineered arcA^–, resulting in a much higher power density than its parental strain toward glycerol oxidation. This work demonstrates that metabolic engineering is a feasible approach to construct efficient bioelectrocatalysts for high-performance MFCs

Functionalization of SnO₂ Photoanode through Mg-Doping and TiO₂‑Coating to Synergically Boost Dye-Sensitized Solar Cell Performance

Mg-doped SnO₂ with an ultrathin TiO₂ coating layer was successfully synthesized through a facile nanoengineering art. Mg-doping and TiO₂-coating constructed functionally multi-interfaced SnO₂ photoanode for blocking charge recombination and enhancing charge transfer in dye-sensitized solar cells (DSC). The designed nanostructure might play a synergistic effect on the reducing recombination and prolonging the lifetime in DSC device. Consequently, a maximum power conversion efficiency of 4.15% was obtained for solar cells fabricated with the SnO₂-based photoelectrode, exhibiting beyond 5-fold improvement in comparison with pure SnO₂ nanomterials photoelectrode DSC (0.85%)

Heteropolyacid-Mediated Self-Assembly of Heteropolyacid-Modified Pristine Graphene Supported Pd Nanoflowers for Superior Catalytic Performance toward Formic Acid Oxidation

The in situ growth of Pd nanoflowers on pristine graphene is achieved using phosphomolybdic acid (HPMo) to mediate self-assembly. The HPMo serves simultaneously as a linker, stabilizer, and structure-directing agent, and the nanoflowers are formed by kinetically controlled growth. When the resulting material, Pd nanoflowers on HPMo-modified graphene (HPMo-G) support, is used to catalyze the formic acid oxidation reaction (FAOR), much higher catalytic activity and durability are found than with HPMo-G supported Pd nanospheres, graphene supported Pd nanoparticles, and commercial Pd/C catalysts. The catalytic activity for Pd nanoflowers on HPMo-G is also among the highest reported for Pd-based catalysts. The superior electrocatalytic performance is attributed to the unique nanoflower shape, a promotion by the HPMo mediator, and the excellent support properties of pristine graphene. The use of HPMo to mediate self-assembly of metals on graphene can be extended to fabricate other hybrid nanostructures promising broad applicability

Local Chemical Environment Dependent Nitrate-Reduction-to-Ammonia Performance on Cu-Based Electrocatalysts

The active component of copper-based materials for electrocatalytic nitrate reduction to ammonia (NRA) remains unclear due to the susceptibility of oxidation of copper. Using density functional theory calculations, NRA pathways are evaluated on low-index crystal surfaces Cu2O (111), CuO (111), and Cu (111) at different pH. Cu2O (111), with abundant undercoordinated Cu atoms on the surface, shows easier adsorption of NO3– than Cu (111) or CuO (111). NRA on CuO (111) is hindered by the large ΔG of adsorption of NO3– and hydrogenation of *NO. Thus, Cu (111) and Cu2O (111) contribute most to the NRA activity while CuO (111) is inert. Three key steps of NRA on copper-based catalysts are identified: adsorption of NO3–, *NO → *NOH/*NHO, and *NH3 desorption, as the three can be rate-determining steps depending on the local environment. Moreover, previous experimentally detected NH2OH on copper-based catalysts may come from the NRA on Cu2O (111) as the most probable pathway on Cu2O (111) is NO3– → *NO3 → *NO2 → *NO → *NHO → *NHOH → *NH2OH → *NH2 → *NH3 → *NH3(g). At high reduction potential, CuOx would be reduced into Cu, so the effective active substance for NRA in a strong reduction environment is Cu

Local Chemical Environment Dependent Nitrate-Reduction-to-Ammonia Performance on Cu-Based Electrocatalysts

The active component of copper-based materials for electrocatalytic nitrate reduction to ammonia (NRA) remains unclear due to the susceptibility of oxidation of copper. Using density functional theory calculations, NRA pathways are evaluated on low-index crystal surfaces Cu2O (111), CuO (111), and Cu (111) at different pH. Cu2O (111), with abundant undercoordinated Cu atoms on the surface, shows easier adsorption of NO3– than Cu (111) or CuO (111). NRA on CuO (111) is hindered by the large ΔG of adsorption of NO3– and hydrogenation of *NO. Thus, Cu (111) and Cu2O (111) contribute most to the NRA activity while CuO (111) is inert. Three key steps of NRA on copper-based catalysts are identified: adsorption of NO3–, *NO → *NOH/*NHO, and *NH3 desorption, as the three can be rate-determining steps depending on the local environment. Moreover, previous experimentally detected NH2OH on copper-based catalysts may come from the NRA on Cu2O (111) as the most probable pathway on Cu2O (111) is NO3– → *NO3 → *NO2 → *NO → *NHO → *NHOH → *NH2OH → *NH2 → *NH3 → *NH3(g). At high reduction potential, CuOx would be reduced into Cu, so the effective active substance for NRA in a strong reduction environment is Cu

One-Pot Synthesis of Co/CoFe₂O₄ Nanoparticles Supported on N‑Doped Graphene for Efficient Bifunctional Oxygen Electrocatalysis

We herein report a facile strategy to synthesize transition metal/spinel oxide nanoparticles coupled with nitrogen-doped graphene (Co/CoFe₂O₄@N-graphene) as an efficient bifunctional electrocatalyst toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This approach involves a spontaneous solution-polymerization of polydopamine (PDA) film on graphene oxide (GO) sheets in the presence of Fe³⁺ and Co²⁺ to form the Fe/Co-PDA-GO precursor, followed by pyrolysis at 800 °C in argon (Ar) atmosphere. During the calcination process, Co/CoFe₂O₄ nanoparticles are in situ formed via high-temperature solid state reaction and are further entrapped by the PDA-derived N-doped carbon layer. As-prepared Co/CoFe₂O₄@N-graphene exhibits highly efficient catalytic activity and excellent stability for both ORR and OER in alkaline solution. This work reports a facile synthetic approach to develop highly active electrocatalysts while offering great flexibility to tailor their components and morphologies and thus provides a useful route to the design and synthesis of a broad variety of electrocatalysts

Hierarchically Porous N‑Doped Carbon Nanotubes/Reduced Graphene Oxide Composite for Promoting Flavin-Based Interfacial Electron Transfer in Microbial Fuel Cells

Interfacial electron transfer between an electroactive biofilm and an electrode is a crucial step for microbial fuel cells (MFCs) and other bio-electrochemical systems. Here, a hierarchically porous nitrogen-doped carbon nanotubes (CNTs)/reduced graphene oxide (rGO) composite with polyaniline as the nitrogen source has been developed for the MFC anode. This composite possesses a nitrogen atom-doped surface for improved flavin redox reaction and a three-dimensional hierarchically porous structure for rich bacterial biofilm growth. The maximum power density achieved with the N-CNTs/rGO anode in S. putrefaciens CN32 MFCs is 1137 mW m^–2, which is 8.9 times compared with that of the carbon cloth anode and also higher than those of N-CNTs (731.17 mW m^–2), N-rGO (442.26 mW m^–2), and the CNTs/rGO (779.9 mW m^–2) composite without nitrogen doping. The greatly improved bio-electrocatalysis could be attributed to the enhanced adsorption of flavins on the N-doped surface and the high density of biofilm adhesion for fast interfacial electron transfer. This work reveals a synergistic effect from pore structure tailoring and surface chemistry designing to boost both the bio- and electrocatalysis in MFCs, which also provide insights for the bioelectrode design in other bio-electrochemical systems

Smart Magnetic Interaction Promotes Efficient and Green Production of High-Quality Fe₃O₄@Carbon Nanoactives for Sustainable Aqueous Batteries

Efficient and green production of monodispersed Fe₃O₄@carbon (C) nanoactives for commercial aqueous battery usage still remains a great challenge due to issues related to tedious hybrid fabrication and purification procedures. Herein, we put forward an interesting applicable synthetic strategy via a general polymeric process and simple magnetic purification treatments, enabling low-cost and massive production of high-quality Fe₃O₄@C hybrids. In such core–shell configurations, all Fe₃O₄ nanoparticles are tightly encapsulated in permeable <i>N</i>-doped C nanoreactors, showing notable nanostructured superiorities as feasible anodes for aqueous batteries. When tested, the Fe₃O₄@C nanoactives exhibit outstanding anodic performance comprising pretty high electrochemical activity/capacity, greatly prolonged cyclic lifespan in contrast to bare Fe₃O₄ counterparts, and prominent rate capabilities. The as-assembled Ni/Fe full cells can even deliver a high energy/power density up to ∼135 Wh kg^–1/11.5 kW kg^–1, further demonstrating their good potential in practical applications. Our smart magnetic purification strategy may hold great promise in addressing critical issues of producing high-quality and affordable Fe₃O₄@C hybrids, not only for energy-storage fields but also in other broad ranges covering catalysts and biosensors

Architecture Engineering of Hierarchically Porous Chitosan/Vacuum-Stripped Graphene Scaffold as Bioanode for High Performance Microbial Fuel Cell

The bioanode is the defining feature of microbial fuel cell (MFC) technology and often limits its performance. In the current work, we report the engineering of a novel hierarchically porous architecture as an efficient bioanode, consisting of biocompatible chitosan and vacuum-stripped graphene (CHI/VSG). With the hierarchical pores and unique VSG, an optimized bioanode delivered a remarkable maximum power density of 1530 mW m^–2 in a mediator-less MFC, 78 times higher than a carbon cloth anode