Understanding the Electrokinetic Role of Ions on Electricity Generation in Droplet-Based Hydrovoltaic Systems

Hydrovoltaic is emerging as a promising energy harvesting technology with the remarkable capability of generating energy through the direct interaction of water and material. The hydrovoltaic generates volt-level potentials without any external force, and its electrical performance can be enhanced by using an aqueous solution. However, it is not clear how salt ions affect or interact with the material. Herein, the theoretical model was used to provide an in-depth analysis of working principles. The model, validated with experimental results, incorporates four physics: water flow in unsaturated porous media, transportation of ions, chemical reactions, and electrostatics. It was found that the distribution of ions is key to improving the voltage output. The higher gradient of ions’ concentration leads to strong potential differences, and its asymmetry of concentration is mainly governed by the water flow and concentration distribution. Additionally, we analyzed the parametric effects of substrate porosity and relative humidity under salt solution. The results showed that the presence of salt ions makes the electrical performance highly sensitive to porosity but less sensitive to relative humidity. Our findings improve the understanding of hydrovoltaic mechanisms and pave the way for the practical use of hydrovoltaic systems

Highly Durable Platinum Catalysts on Nano-SiC Supports with an Epitaxial Graphene Nanosheet Layer Grown from Coffee Grounds for Proton Exchange Membrane Fuel Cells

Robust ceramic supports have attracted significant attention as alternatives to carbon supports for proton exchange membrane fuel cells (PEMFCs). However, they suffer from lower electrocatalytic activities than carbon-based supports because of their electrical conductivity. Here, SiC nanopowders were modified with epitaxial graphene and evaluated as the support for Pt in PEMFCs. Coffee grounds are used as a carbon source to not only enhance the electrocatalytic activity of the graphene-modified SiC supports but also demonstrate the feasibility of exploiting and commercializing this widely available waste product. The Pt-decorated ceramic supports deliver the enhanced durability and performance under the accelerated electro′chemical conditions

Hollow Heteropoly Acid-Functionalized ZIF Composite Membrane for Proton Exchange Membrane Fuel Cells

Heteropoly acids (HPAs) have been used in perfluorinated sulfonic acid polymers such as Nafion or Aquivion to form organic/inorganic composite membranes with improved proton conductivity and water management ability. However, the HPA has a low BET surface area with water-soluble characteristics, which prevents enhancement in the number of proton-transferable sites and accelerates HPA leaching while operating the proton exchange membrane fuel cells (PEMFCs). The HPA was functionalized on zeolite imidazolate framework-67 (ZIF-67) nanoparticles to address these drawbacks. Incorporating it into the MOF made it water insoluble and enhanced the internal surface area, leading to a good proton conductor. Using a synthetic approach, we were able to form HPA-functionalized ZIF-67 (HZF), which can be optimized with simple compositional modifications and whose HPA content is controllable. The HZF nanoparticles exhibited a hollow structure that formed an HPA–ZIF shell layer because the dissociated cobalt ion and 2-methylimidazole diffused from the core side to the surface layer to interact with the HPA. The HZF/Aquivion composite membranes exhibited excellent mechanical properties and good resistance to the polymer chain swelling phenomenon. The electrochemical properties of the HZF/Aquivion composite membranes with various HZFs were characterized to determine the optimal HPA content in the HZF nanoparticles. The 3 wt % hollow HZF/Aquivion composite membrane with the appropriate HPA content exhibited higher proton conductivities than the pure Aquivion membrane, measuring 0.14 S/cm at 25 °C and 100% RH and 0.09 S/cm at 80 °C and 30% RH. This result indicates that the hollow HZF/Aquivion composite membrane can provide efficient proton transfer and water management ability, suggesting a good strategy for the PEMFC operation