Liling Wei

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.

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.

“Spontaneous bubble-template” assisted metal–polymeric framework derived N/Co dual-doped hierarchically porous carbon/Fe3O4 nanohybrids: superior electrocatalyst for ORR in biofuel cells

A “Spontaneous bubble-template” method is fascinating in that bubbles are formed in situ during material processing and employed as a template for fabricating unique structures, which has not been reported in material science. It is sustainable, green and efficient in that no extra additives or post-treatment are used. Herein, novel metal–polymeric framework derived hierarchically porous carbon/Fe3O4 nanohybrids are prepared using a “spontaneous bubble-template” method by one-step carbonization. During the carbonization process, N and Co are self-doped on porous carbon in which in situ grown nano Fe3O4 is embedded (Fe3O4@N/Co–C). The as-prepared Fe3O4@N/Co–C displays a three-dimensional interpenetrating morphology (electrochemical active area: 729.89 m2 g−1) with well-distributed Fe3O4 nanoparticles (20–50 nm) which are coated with a carbon layer (3–5 nm). Fe3O4@N/Co–C exhibits remarkable oxygen reduction activity in biofuel cells with a distinct output voltage (576 mV) and power density (918 mW m−2), which are 3.6% and 17.8% higher than those of Pt (0.5 mg cm−2), respectively. Besides biofuel cells, Fe3O4@N/Co–C may also have the potential for application in chemical fuel cells, since it demonstrates better oxygen reduction activity in electrochemical measurements. Thus, with the virtues of its low-cost, facile synthesis and large-scale preparation, Fe3O4@N/Co–C is a promising electrocatalyst for the oxygen reduction reaction and application in biofuel cells.

A graphene modified biocathode for enhancing hydrogen production

Biocathodes have shown great promise for developing low-cost cathodes for hydrogen production in microbial electrolysis cells (MEC). To promote the performance of hydrogen production with a biocathode, we constructed a graphene modified biocathode and assessed the performance of the modified biocathode by setting different cathode potentials. The results indicated that it was feasible to promote the current density, electron recovery efficiency (ERE) and hydrogen production rate by a modified biocathode using graphene. At −1.1 V (vs. Ag/AgCl), the hydrogen production rate of the graphene modified biocathode even achieved 2.49 ± 0.23 m3 per m3 per day with 89.12 ± 6.03% of ERE at a current density of 14.07 ± 0.06 A m−2, which were about 2.83 times, 1.38 times and 2.06 times that of the unmodified biocathode, respectively. The hydrogen production performance of the graphene modified biocathode was close to that of the platinum catalyzed cathode and superior to that of the stainless steel mesh cathode at −1.1 V.

Enhanced power generation using nano cobalt oxide anchored nitrogen-decorated reduced graphene oxide as a high-performance air-cathode electrocatalyst in biofuel cells

So far, the effect of the carbon matrix on ORR catalytic efficiency over carbon/cobalt oxide nanohybrids in biofuel cells has not been investigated, which is vital to guiding the scientific research on ORR catalysts. Moreover, although cobalt oxide crystals have been reported with electrocatalytic activity, studies on square-like nano cobalt oxide are very few, and it has not been reported as an oxygen reduction reaction (ORR) catalyst, let alone used in biofuel cells. Thus, herein, square-like nano cobalt oxide anchored on nitrogen-doped graphene (NG/Co-NS), carbon nanotube (CNT/Co-NS) and carbon black (CB/Co-NS) were prepared by a one-pot hydrothermal method for the application as an ORR catalyst in microbial fuel cells (MFC). The results indicated that NG/Co-NS exhibited outstanding ORR activity with a more positive on-set potential (−0.05 V vs. Ag/AgCl) and higher limiting diffusion current (5.8 mA cm−2 at −0.8 V) than CB/Co-NS and CNT/Co-NS, attributed to the synergistic catalytic effect of NG and Co-NS. Besides, in MFC tests, the maximum power density of NG/Co-NS was improved significantly to 713.6 mW m−2, which was 24.9% higher than Pt/C (571.3 mW m−2, 0.2 mg Pt cm−2). In addition, the internal resistance of MFCs with NG/Co-NS was lower than CB/Co-NS and CNT/Co-NS, which favored the electricity generation performance. Thus, NG/Co-NS was promising material for an alternative oxygen reduction reaction electrocatalyst of Pt/C in MFCs.

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.

A polyaniline-derived iron–nitrogen–carbon nanorod network anchored on graphene as a cost-effective air-cathode electrocatalyst for microbial fuel cells

A highly active and cost-effective Pt-free catalyst for oxygen reduction reaction (ORR) is significantly important for air-cathode microbial fuel cells (MFCs). In this study, a novel low-cost iron–nitrogen–carbon nanorod network-anchored graphene (Fe–N–C/G) nanohybrid was prepared for use as an efficient ORR catalyst. The morphology, chemical composition, and ORR catalytic activity of the as-prepared Fe–N–C/G were investigated by a series physical measurements and electrochemical tests. Finally, it the nanohybrid was employed as an ORR electrocatalyst in the practical air-cathode MFCs. Remarkably, Fe–N–C/G exhibited a comparable catalytic performance and stability in a neutral medium along with even better power generation performance (1601 ± 59 mW m−2) in MFCs as compared to the-state-of-the-art Pt/C catalyst (1468 ± 58 mW m−2). The superior ORR activity of Fe–N–C/G should be attributed to its N/Fe co-doping, the introduction of graphene, as well as the unique micro-nano structure, which can dramatically favor the oxygen reduction kinetics. Therefore, the cost-effective Fe–N–C/G can be one of the most promising ORR catalysts for application in a neutral medium and practical air-cathode MFCs.