NiFe codoping-regulated amorphous/crystalline heterostructured Co-based hydroxides/tungstate with rich oxygen vacancies for efficient water oxidation catalysis.

Oxygen evolution reaction (OER) is a crucial half-reaction in water splitting, generating hydrogen for sustainable development, but it is often subject to sluggish kinetics. Abundant transition metal-based OER electrocatalysts have been utilized to expedite the process. However, traditional amorphous catalysts suffer from low conductivity, while the activity of crystalline catalysts is also unsatisfactory. Herein, an amorphous/crystalline heterostructured Co-based hydroxide/tungstate was meticulously constructed and further tailored using a NiFe codoping method (NiFeCoW). Following NiFe codoping, the electronic structure had been modulated, subsequently altering the adsorption toward intermediates. From the electrochemical measurements, the NiFeCoW catalyst demonstrated superior electrocatalytic activity for OER in alkaline media, with a minimal overpotential of 297 mV at 10 mA cm-2 and a cell voltage of 1.57 V for water splitting. This study provides valuable guidance for regulating the amorphous/crystalline heterophase in catalysts through bimetallic modulating engineering.

Iron/cobalt-decorated nitrogen-rich 3D layer-stacked porous biochar as high-performance oxygen reduction air-cathode catalyst in microbial fuel cell.

Developing low-cost and high-efficiency oxygen reduction reaction (ORR) catalysts is crucial to the commercial application of microbial fuel cell (MFC). Herein, Fe/Co-decorated nitrogen-rich three-dimensional (3D) layer-stacked porous biochar (Fe/Co-NC-x) have been synthesized from silk gel through secondary carbonization of activated carbons which firstly adsorbed metal ions. The multilayer porous structure of Fe/Co-NC-3 contributes to construction of high specific surface area (576 m2 g-1), large pore volume (1.27 cm3 g-1) and many defect structure (ID/IG = 1.004). As expected, with Fe/Co synergistic effect, Fe/Co-NC-3 exhibits excellent ORR performance through 4e- pathway with good methanol resistance. In addition, the performance of MFC using Fe/Co-NC-3 as air-cathode catalyst is more prominent with higher maximum power density (1059.62 ± 30.00 mW m-2) compared to that using NC (668.19 ± 9.84 mW m-2) and commercial Pt/C catalyst (957.33 ± 10.50 mW m-2). Therefore, Fe/Co-NC-3 should be a prospective catalyst in the practical application of fuel cells and other energy devices.

Hollow N-doped bimetal carbon spheres with superior ORR catalytic performance for microbial fuel cells.

Herein, we report the fabrication of bimetal ZIF-derived Cu/Co/N co-doped hollow spheres as effective oxygen reduction reaction (ORR) catalysts by the pyrolysis of core-shell polystyrene@Cu/Co-ZIFs (PS@Cu/Co-ZIFs) composite precursors. As a thermally degradable template, PS spheres are a key to determine the catalyst size. The bimetal ZIF hollow spheres were synthesized via a simple carbonization reaction, where ZIFs shells formed on PS spheres after the addition of metal sources, (Co(NO3)2 and Cu(NO3)2), and organic ligand 2-methylimidazole. Benefiting from the hollow structural and abundant catalytic sites, the as-prepared Cu/Co/N-doped hollow spheres showed superior electrocatalytic performances and excellent durability than commercial Pt/C catalysts. The on-set and half-wave potentials of the Cu/Co/N-HS-3 catalyst were 0.25 and 0.13 V (vs Ag/AgCl), respectively, which were greater than those of 20% Pt/C catalysts (0.24 and 0.12 V). Moreover, the Cu/Co/N-HS-3 catalyst-based air-cathode microbial fuel cells (MFCs) exhibited maximum output voltage and power density of 620 mV and 1016 mW/m2, respectively, demonstrating superiority to commercial Pt/C catalyst-based MFCs (586 mV and 908 mW/m2).

A pyridine-Fe gel with an ultralow-loading Pt derivative as ORR catalyst in microbial fuel cells with long-term stability and high output voltage.

A low-cost and high-efficiency oxygen reduction reaction (ORR) catalyst was fabricated using a pyridine-Fe gel with ultralow-loading of Pt nanoparticles and subsequently applied to air-cathode microbial fuel cells (MFCs). This novel catalyst (N3/Fe/C-Pt) exhibited excellent electrocatalytic activity with a positive onset potential of 0.19 V (vs Ag/AgCl) and half-wave potential of 0.03 V (vs Ag/AgCl), which is comparable to commercial PtC catalysts. More importantly, N3/Fe/C-Pt shows remarkable oxygen reduction activity in MFCs with a distinct output voltage (568 mV) and power density (504 mW m-2) for 400 h when it is fed with a culture medium containing 5 g L-1 sucrose in the phosphate buffer solution. This strategy, incorporating Pt nanoparticles uniformly into a conductive gel demonstrates significance for broadening the development and research of gel-based catalysts for applications in batteries.

Salt-induced silk gel-derived N and trace Fe co-doped 3D porous carbon as an oxygen reduction catalyst in microbial fuel cells.

Inexpensive and high-efficiency oxygen reduction reaction (ORR) catalysts play a significant role in achieving practical applications of microbial fuel cells (MFCs). Hence, herein, novel nitrogen (N) and trace iron (Fe) co-doped three-dimensional (3D) porous carbon (NFex-C) was synthesized as an excellent ORR catalyst from an interesting salt-induced silk gel, which was beneficial to the spontaneously formation of porosity and boosted the ORR activity. Among the series of NFex-C, NFe0.5-C (1.20% N-ORR/C, 0.07 at% Fe) possessed a higher specific surface area (538.94 m2 g-1) and pore volume (2.158 cm3 g-1). Note that NFe0.5-C exhibited a significantly higher positive initial potential (0.274 V vs. Ag/AgCl) and half-wave potential (0.095 V vs. Ag/AgCl) than other catalysts and commercial Pt/C (20 wt%); this implied that it possessed prominent ORR catalytic activity. In the MFC tests, the output-voltage and maximum power density of NFe0.5-C were enhanced to 517.37 ± 7.87 mV and 605.35 ± 15.39 mW m-2, respectively. Moreover, NFe0.5-C (0.15 $ g-1) exhibits excellent anti-poisoning ability and is thousands of times cheaper than commercial Pt/C (20 wt%, 220.04 $ g-1); therefore, NFe0.5-C should be a prospective catalyst to substitute precious commercial Pt/C in MFCs and even for application in other types of fuel cells.

Gas-Flow Tailoring Fabrication of Graphene-like Co-Nx-C Nanosheet Supported Sub-10 nm PtCo Nanoalloys as Synergistic Catalyst for Air-Cathode Microbial Fuel Cells.

In this work, we presented a novel, facile, and template-free strategy for fabricating graphene-like N-doped carbon as oxygen reduction catalyst in sustainable microbial fuel cells (MFCs) by using an ion-inducing and spontaneous gas-flow tailoring effect from a unique nitrogen-rich polymer gel precursor which has not been reported in materials science. Remarkably, by introduction of trace platinum- and cobalt- precursor in polymer gel, highly dispersed sub-10 nm PtCo nanoalloys can be in situ grown and anchored on graphene-like carbon. The as-prepared catalysts were investigated by a series of physical characterizations, electrochemical measurements, and microbial fuel cell tests. Interestingly, even with a low Pt content (5.13 wt %), the most active Co/N codoped carbon supported PtCo nanoalloys (Co-N-C/Pt) exhibited dramatically improved catalytic activity toward oxygen reduction reaction coupled with superior output power density (1008 ± 43 mW m-2) in MFCs, which was 29.40% higher than the state of the art Pt/C (20 wt %). Notability, the distinct catalytic activity of Co-N-C/Pt was attributed to the highly efficient synergistic catalytic effect of Co-Nx-C and PtCo nanoalloys. Therefore, Co-N-C/Pt should be a promising oxygen reduction catalyst for application in MFCs. Further, the novel strategy for graphene-like carbon also can be widely used in many other energy conversion and storage devices.

Superiority of boron, nitrogen and iron ternary doped carbonized graphene oxide-based catalysts for oxygen reduction in microbial fuel cells.

The exploration of highly active and cost-effective catalysts for the oxygen reduction reaction is vitally important to facilitate the improvement of metal-air batteries and fuel cells. Herein, super-active catalysts made from an interesting metal-polymer network (MPN) that consist of Fe-Nx-C, B-N and Fe3O4/Fe3C alloys were prepared via facile one-pot carbonization. The achieved catalysts possessed an amazing porous structure that was derived from the MPN with the assistance of a "bubble-template". Remarkably, the content of highly active Fe-Nx-C can be regulated by introducing graphene, and the ORR activity of the catalyst was enhanced dramatically with an increase in the Fe3O4/Fe3C alloy content. The most active BNFe-C-G2 catalyst exhibited superior ORR activity/stability, and was then employed as an air cathode electrocatalyst in a microbial fuel cell. The results showed that the output voltage and power density of BNFe-C-G2 were significantly improved to 575 ± 11 mV and 1046.2 ± 35 mW m-2, respectively. These values are 4.5% and 44.44% higher than those of commercial Pt/C. Thus, due to the synergistic electrocatalysis of the Fe-Nx-C, B-N and Fe3O4/Fe3C alloys, the super-active and low-cost BNFe-C-G2 material should be a promising ORR catalyst for application in biofuel cells, and in many other energy conversion and storage devices.

Low-cost adsorbent derived and in situ nitrogen/iron co-doped carbon as efficient oxygen reduction catalyst in microbial fuel cells.

A novel low-cost adsorbent derived and in situ nitrogen/iron co-doped carbon (N/Fe-C) with three-dimensional porous structure is employed as efficient oxygen reduction catalyst in microbial fuel cells (MFCs). The electrochemical active area is significantly improved to 617.19m(2)g(-1) in N/Fe-C by Fe-doping. And N/Fe-C (4.21at.% N, 0.11at.% Fe) exhibits excellent electrocatalytic activity with the oxygen reduction potential of -0.07V (vs. Ag/AgCl) which is comparable to commercial Pt/C. In MFCs tests, the maximum power density and output voltage with N/Fe-C are enhanced to 745mWm(-2) and 562mV (external resistance 1kΩ), which are 11% and 0.72% higher than Pt/C (0.5mgPtcm(-2)), respectively. Besides, the long-term stability of N/Fe-C retains better for more than one week. Moreover, the charge transfer resistance (Rct) values are recorded by the impedance measurements, and the low Rct of N/Fe-C is also result in better catalytic activity.

Enhancement effect of hematite nanoparticles on fermentative hydrogen production.

The effects of hematite nanoparticles concentration (0-1600 mg/L) and initial pH (4.0-10.0) on hydrogen production were investigated in batch assays using sucrose-fed anaerobic mixed bacteria at 35°C. The optimum hematite nanoparticles concentration with an initial pH 8.48 was 200mg/L, with the maximum hydrogen yield of 3.21 mol H(2)/mol sucrose which was 32.64% higher than the blank test. At 200mg/L hematite nanoparticles concentration, further initial pH optimization experiments indicated that at pH 6.0 the maximum hydrogen yield reached to 3.57 mol H(2)/mol sucrose and hydrogen content was 66.1%. The slow release of hematite nanoparticles had been recorded by transmission electron microscopy (TEM). In addition, TEM analysis indicated that the hematite nanoparticles can affect the shape of bacteria, namely, its length increased from ca. 2.0-3.6 µm to ca. 2.6-5.6 µm, and width became narrower.

Effects of culture and medium conditions on hydrogen production from starch using anaerobic bacteria.

The influences of initial pH (4.0-9.0), iron concentration (1.2-100 mg/l), nitrogen concentration (NH4HCO3, 0.56-11.28 g/l) and starch concentration (2-32 g/l) on hydrogen production and volatile fatty acid (VFA) production were studied. Batch experiments using starch as a substrate and mixed bacteria were conducted at 35 degrees C. The optimum pH, iron concentration and nitrogen concentration for hydrogen production at a starch concentration of 15 g/l were 7.0-8.0, Fe2+ 10 mg/l and NH4HCO3 5.64 g/l, respectively. The typical VFAs were acetate, propionate and butyrate, with acetate as the major component. The maximum specific hydrogen production rate of 146 ml/g-VSS.d (volatile suspended solids, VSS) and the hydrogen yield of 178 ml/g-starch were obtained at a starch concentration of 15 g/l under optimum environmental conditions. The maximum hydrogen yield of 194 ml/g-starch was obtained at a starch concentration of 2 g/l. The maximum specific hydrogen production rate of 237 ml/g-VSS.d was found at a starch concentration of 24 g/l.

Active oxygen species (1O2, O2*-) generation in the system of TiO2 colloid sensitized by hypocrellin B.

TiO2 semiconductor colloids have been successfully employed in environmental clean-up, antibacterial and bactericidal action under ultraviolet light due to its strong redox ability and high yield of active oxygen species (1O2, O2*-), *OOH) generation. Hypocrellin B, isolated from Hypocrella bambusae (B.et.Br) Sacc, a natural pigment with strong and broad absorption over the visible light region, was used in our work in an attempt to extend the photoresponse of TiO2 to visible light and maintain the high generation of active oxygen under visible light illumination. The formation of the HB-TiO2 chelate was characterized by UV-Vis and surface enhanced raman spectroscopy (SERS) and it was found that the chelate still had high efficiency of active oxygen generation. The possible generation mechanism was explored by Electron Paramagnetic Resonance (EPR) and time-resolved transient spectra techniques, showing that singlet oxygen (1O2) and superoxide radical anion (O2*-)) were produced via energy transfer and electron transfer, respectively. The application of HB-TiO2 chelate in environment protection and bacteria sterilization was implied.