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As society advances, there is an increasing demand to solve the worsening issues surrounding energy depletion and environmental pollution. Researchers are always striving for new ways to produce clean energy and reduce our footprint on the environment. A team of Researchers from China have now developed an innovative method to produce porous carbon materials using sewage sludge, and thus, acts an environmentally friendly way to recycle sludge.
There are current demands to find new ways to produce clean energy, with alkaline fuel cells being one potential solution due to their low emissions and high efficiencies. However, the catalytic, cathodic materials within these fuels are not ready for commercial use. Currently, many of the electrodes employ a Pt/C hybrid material which is not only expensive, but the catalytic activity can’t meet the application demands.
Striving to increase the commercial potential of fuel cells, the Researchers came up with a very clever route to not only produce new carbon materials, but also a process that helps to alleviate other environmental concerns by recycling waste sludge and using it as a carbon source.
Urban sludge is currently a problem in many areas and traditional sludge disposal methods take up a lot of space, pose a security risk and are of high cost. As such, the ability to convert the components within the sludge, as to maximize available resources, into usable materials is seen as having the most potential for solving the problems associated with municipal sludge pollution.
Sewage sludge is mostly composed of organic matter, alongside proteins and inorganic oxides, making it an ideal starting material and carbon source. The conversion of sludge into heteroatom-doped carbon materials appears to be the most useful way going forward, for both electrode production and environmental impact.
The Researchers utilized a cation ion exchange reaction to develop a multi-doped porous graphene/carbon material. The Researchers used an oxygen reduction reaction, utilizing the sludge as the carbon source, with doped heteroatoms and a template composed of Fe-pillared montmorillonite. The result was a three-dimensional carbon nanomaterial with a graphene-style structure.
To characterize the material(s), the Researchers used thermo-gravimetric and differential scanning calorimetry (TG-DSC, STA-449F3 Netasch), scanning electron microscopy (SEM, Carl Zeiss), transmission electron microscopy (TEM, JEM- 3010, JEOL Ltd), X-ray diffraction (XRD, D8-Advance), Fourier-transform infrared spectroscopy (FTIR, American 96 Thermo-electron Corporation), Raman spectroscopy (Renishaw in Via Reflex), chemisorption surface area analysis (ASAP 2010, Micromeritics) and X-ray photoelectron spectroscopy (XPS, AES430S, ANELVA). Electrochemcial measurements were performed using an electrochemical workstation (CHI 660E, Shanghai Chenhua Instrument Co), which allowed for both cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements to be taken.
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The reaction made full use of the carbon, nitrogen and iron atoms in the sludge and took advantage of the expandable interlayer structure and the templating effect of Fe-pillared montmorillonite Fe-Mt). The structure produced from the Fe-Mt pillars was found to be the most useful, and possessed the highest specific surface area, ORR activity, ability for immune methanol crossover and durability in an alkaline medium.
These properties were also found to be superior to 20 wt% platinum electrodes that are used commercially. The removal and recycling of the sludge, i.e. the oxygen reduction reaction, was also found to be more efficient using the Iron-pillared method.
The material produced from using Fe-Mt pillars has been denoted as Fe-Mt-SS-C. This material also possessed an enhanced electrocatalytic ORR activity through possessing more adsorption sites and a more efficient electronic structure, than the other materials produces. This ultimately increased the conductivity and electrochemical activity of the electrode material.
The value of the onset potential (0.03V) and E1/2 (−0.09V) of Fe-SS-C was found to be better than commercially available 20 wt% Pt/C electrodes. (−0.02V and −0.18V, respectively). The excellent ORR activity of the material has been attributed to the synergistic effect between the 3D porous structure, a high degree of graphitization and a large amount of defect and doped atoms.
Not only have the Researchers found an environmentally-friendly way to produce carbon materials that could be used for green energy applications, they have also found a novel way to recycle waste sludge in the same process. There is also great potential for the FE-Mt-SS-C material to be used commercially a high-efficiency ORR electrocatalyst.
Sources and Further Reading
- “Three-Dimensional Multi-Doped Porous Carbon/Graphene Derived from Sewage Sludge with Template-Assisted Fe-pillared Montmorillonite for Enhanced Oxygen Reduction Reaction”- Chen M.,