Päärn Paiste

The electrochemical activity of two binary alloy catalysts toward oxygen reduction reaction in 0.1 M KOH

The platinum group metals (Pt, Ir and Ru) and the carbide-derived carbon support with the very high specific surface area were used to synthesise the low noble metal loading Pt-C, IrPt-C and RuPt-C alloy catalysts. The alloying of the platinum group metals in the studied catalysts was proved by the several independent physical characterization methods like: the X-ray diffraction, time of flight secondary ion mass-spectrometry, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The electrocatalytic activity toward oxygen reduction reaction of the synthesised catalysts in an alkaline solution was studied and compared with the commercially available Pt-Vulcan. The combined and detail approach using the transmission electron microscopy and inductively coupled plasma mass spectrometry for estimation of the surface area of metal particles is provided. The noticeably higher calculated mass corrected and specific kinetic current density values for Pt-C catalyst were established. For IrPt-C and RuPt-C alloy catalysts, mass corrected current density values are comparable with the commercial Pt-Vulcan. The specific kinetic current density values increase in the following sequence: RuPt-C < IrPt-C < Pt-Vulcan < Pt-C.

Biochar enhances plant growth and nutrient removal in horizontal subsurface flow constructed wetlands

Biochar has shown great potential as an amendment to improve soil quality and promote plant growth, as well as to adsorb pollutants from water. However, information about the effect of biochar on the wastewater treatment efficiency in horizontal subsurface flow (HSSF) constructed wetlands (CWs) is still scarce. In this study, we assessed the effect of biochar amendment on the purification efficiency of pretreated municipal wastewater in planted (Typha latifolia) experimental horizontal subsurface flow filters filled with lightweight expanded clay aggregates (LECA). The addition of wood-derived biochar (10% v/v) to LECA significantly increased plant biomass production and enhanced the wastewater treatment efficiency of the planted filters. Both the aboveground plant biomass and belowground plant biomass were higher (1.9- and 1.5-fold, respectively) in the filters of the LBP (LECA + biochar + plants) treatments compared to the LP (LECA + plants) filters. The water pH was significantly lower in the planted filters (LBP < LP < LB-LECA + biochar). The efficiencies of TN and TP removal from wastewater were highest in the LBP filters (20.0% and 22.5%, respectively), followed by the LP (13.7% and 16.2%, respectively) and LB (9.5% and 15.6%, respectively) filters. More N and P were incorporated into the plant biomass from wastewater in the presence of biochar in the filter medium. The study results confirm that biochar can be an advantageous supplement for planted HSSF CWs to enhance the treatment efficiency of these systems.

Synthesis of highly-active Fe–N–C catalysts for PEMFC with carbide-derived carbons

Proton exchange membrane fuel cells (PEMFC) offer a viable alternative to internal combustion engines, but highly performing stacks still require large amounts of platinum-based catalysts. Fe–N–C catalysts have recently emerged as potential substitutes. Carbide-derived carbon (CDC) can be designed to have various pore size distributions (PSD), in the microporous and/or mesoporous domains, which can be used for defining the number and/or accessibility of active sites in Fe–N–C catalysts based on the CDC. In this work, we compare two sets of Fe–N–C catalysts derived from two different CDCs, one with most frequent pore size of 8.5 A, (CDC-2) and another one with most frequent pore sizes at 7.8 and 30 A (CDC-1). The CDC-based Fe–N–C catalysts show excellent half-wave potential for oxygen reduction reaction (ORR) of 0.81 V vs. RHE in 0.5 M H2SO4. This work presents the first study of CDC-based catalysts in a PEMFC, where the performance of the CDC-2 based catalyst rivaled that of the best Fe–N–C materials in the literature. The catalyst derived from CDC-2 showed ca. 5 times higher activity at 0.8 V vs. RHE than the one derived from CDC-1. We show that the residual presence of boron in CDC-1 is the main reason for the lower activity of CDC-1 derived catalysts, leading to the formation of iron boride instead of ORR-active FeNxCy moieties. Higher Fe contents were investigated for CDC-2, but lead to unmodified activity, which is explained from Mossbauer spectroscopy measurements by the increasing formation of ORR-inactive Fe species at high Fe content. In summary, we demonstrate the excellent potential for CDC materials to be used in catalyst design and also identify some key issues that may arise from the possible residual presence of secondary atoms from the starting carbide.