Browsing by Author "Suominen, Milla"

Now showing 1 - 14 of 14

Bimetallic electrocatalysts for hydrogen evolution and oxidation reaction in alkaline media
(2023-08-22) Hammouali, Amine
Kemian tekniikan korkeakoulu | Master's thesis
The present work Focus on synthesizing platinum-based bimetallic catalysts with a metallic atomic ratio of 1:1, supported on ozone-treated carbon nanotubes, for applications in hydrogen evolution and hydrogen oxidation reactions in alkaline media. The synthesized materials are comprehensively characterized to determine their physical properties including structures, dispersion, and morphology. Additionally, the chemical composition is measured to determine the output metallic ratio. Initial results indicate unsatisfactory outcomes, suggesting a need for further investigation. The materials are extensively evaluated in term of their catalytic performances toward hydrogen evolution and hydrogen oxidation reactions in alkaline media. The primary objective is to establish a correlation between the oxophilicity of the second metal and the observed catalytic performances. Promising trends are being identified in the performance of the bimetallic catalyst, indicating the potential influence of the second metal on the catalyst's performance. However, further studies are required to validate these findings.
Construction of hydrophilic-hydrophobic domains in Bi2O3/nitrogen-doped carbon electrode to boost CO2-to-formate conversion
(2024-04) Shi, Junjie; Han, Nana; Jin, Benjin; Suominen, Milla; Lahtinen, Jouko; Miikki, Kim; Wilson, Benjamin P.; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Bi has drawn attention in catalyzing the electrochemical CO2-to-formate conversion due to promising selectivity and low cost, but the process suffers from low activity. Herein, we introduce nitrogen-doped carbon (NC) support with hydrophobicity modification to enhance the activity of a binder-free Bi2O3 electrode. Formate partial current on the NC supported Bi2O3 electrode almost doubles compared to Bi2O3 on unmodified support. Furthermore, the hydrophobicity modification with polytetrafluoroethylene (PTFE) significantly extends the stability of NC supported Bi2O3 by diminishing flooding. It also maintains >90% formate selectivity at a broad potential range from −0.87 to −1.27 V (vs. RHE) and shows a formate partial current density of −100 mA cm−2 at −1.37 V (vs. RHE) in 0.5 M KHCO3. The improvement is attributed to the synergetic effects of the hydrophilic active sites and the hydrophobic PTFE modified NC support. The unique structure promotes the reactants transport and thus maximizes the active site utilization at the triple-phase interface. This facile microenvironment regulation can be extended to other applications involving gaseous-aqueous phases.
Effects of carbon support ozonation on the electrochemical reduction of CO2 to formate and syngas in a flow cell on Pd nanostructures
(2024-12) Suominen, Milla; Shi, Junjie; Sainio, Jani; Hammouali, Amine; Moumaneix, Lilian; Kobets, Anna; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Pd convers electrochemically CO2 into formate at the most positive known potentials but with low activity. Additionally, Pd is CO selective at more negative potentials, but is poisoned by the strongly bound CO∗ intermediate. Improving the activity and stability of Pd-based electrocatalysts holds promise for improving the electrochemical production of formic acid. Herein, we studied the effects of carbon support and its ozonation on the selectivity of electrochemical CO2 reduction on Pd. The ozone treatment is found to improve the activity and formate selectivity at low overpotentials on single-walled carbon nanotube-supported catalysts with partial current densities up to −12 mA cm−2 in 0.5 M KHCO3 at potentials of −0.35 V and −0.45 V (vs. RHE). At more negative potentials, the catalysts become more selective towards CO and an opposite trend for CO-selectivity and ozonation duration is demonstrated. Unfortunately, the materials show deactivation in the form of decreased formate selectivity and increased hydrogen and CO evolution, especially when supports treated with ozone for a longer duration. The results and possible mechanisms are discussed based on previous findings and the physicochemical characterizations of the prepared catalysts. This work shows that a simple ozone treatment of carbons changes the efficiency of CO2 electroreduction.
Electrochemical reduction of CO2 on a CoTPP/MWCNT composite: Investigation of operation parameters influence on CH3OH production by differential electrochemical mass spectrometry (DEMS)
(2024-10) Hossain, Md Noor; Suominen, Milla; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Renewable electricity-driven electrochemical production of small organic molecules, such as CH3OH, from chemical industry waste CO2 feedstock is highly desirable for circular economy. These reactions proceed via multiple intermediate steps which causes high overpotential and poor selectivity imposing a challenge for designing techno-economically viable systems. Proper understanding of the reaction mechanism is essential to overcome those challenges. Herein, we present a simple qualitative analysis to understand the reaction mechanism during electrochemical reduction of CO2 (eCO2R) on a cobalt tetraphenylporphyrin / multiwalled carbon nanotube (CoTPP/MWCNT) composite in the temperature range of 20–50 °C by employing differential electrochemical mass spectrometry (DEMS) in 0.1 M and 0.5 M KHCO3 electrolytes. Interestingly, temperature is observed to strongly affect the onset potentials for product generation in such a way that with the increase of temperature from 20 °C to 50 °C a decrease in the onset potential specifically for methanol formation is observed. Moreover, formaldehyde (HCHO) formation appears to occur at lower overpotentials before the formation of CH3OH which suggests that on the composite electrocatalyst, HCHO is an important intermediate on a route to CH3OH. This work offers valuable information on reaction routes to CH3OH and temperature effects on the eCO2R selectivity on molecular catalysts.
Epäpuhtaudet hiilidioksidin sähkökemiallisessa pelkistyksessä
(2023-06-02) Nyblom, Kaisla
Kemiantekniikan korkeakoulu | Bachelor's thesis
Experimental and Computational Study Toward Identifying Active Sites of Supported SnOx Nanoparticles for Electrochemical CO2 Reduction Using Machine-Learned Interatomic Potentials
(2024-10-03) Shi, Junjie; Pršlja, Paulina; Jin, Benjin; Suominen, Milla; Sainio, Jani; Jiang, Hua; Han, Nana; Robertson, Daria; Košir, Janez; Caro, Miguel; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
SnOx has received great attention as an electrocatalyst for CO2 reduction reaction (CO2RR), however; it still suffers from low activity. Moreover, the atomic-level SnOx structure and the nature of the active sites are still ambiguous due to the dynamism of surface structure and difficulty in structure characterization under electrochemical conditions. Herein, CO2RR performance is enhanced by supporting SnO2 nanoparticles on two common supports, vulcan carbon and TiO2. Then, electrolysis of CO2 at various temperatures in a neutral electrolyte reveals that the application window for this catalyst is between 12 and 30 °C. Furthermore, this study introduces a machine learning interatomic potential method for the atomistic simulation to investigate SnO2 reduction and establish a correlation between SnOx structures and their CO2RR performance. In addition, selectivity is analyzed computationally with density functional theory simulations to identify the key differences between the binding energies of *H and *CO2−, where both are correlated with the presence of oxygen on the nanoparticle surface. This study offers in-depth insights into the rational design and application of SnOx-based electrocatalysts for CO2RR.
Karbidien käyttö sähkökemiallisessa hiilidioksidin pelkistyksessä
(2020-12-21) Räisänen, Pinja
Kemiantekniikan korkeakoulu | Bachelor's thesis
Karbidien käyttö sähkökemiallisessa hiilidioksidin pelkistyksessä
(2020-12-21) Räisänen, Pinja
Kemiantekniikan korkeakoulu | Bachelor's thesis
Katalyytit hiilidioksidin sähkökemiallisessa pelkistämisessä muurahaishapoksi
(2021-05-24) Partanen, Olga
Kemiantekniikan korkeakoulu | Bachelor's thesis
Mn-doped Bi2O3 grown on PTFE-treated carbon paper for electrochemical CO2-to-formate production
(2024-12) Shi, Junjie; Pršlja, Paulina; Suominen, Milla; Jin, Benjin; Lahtinen, Jouko; Moumaneix, Lilian; Kong, Xiangze; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
BiOx shows promising selectivity in catalyzing the electrochemical reduction of CO2 to formate, but the process suffers from high overpotential and a low rate. Moreover, the active sites are still ambiguous under electrochemical conditions. Herein, we introduce Mn-doping to enhance the activity of binder-free Bi2O3 and elaborate on active sites through in situ Raman and density functional theory (DFT) analyses. The Mn-doped Bi2O3 transforms to Mn-doped Bi2(CO3)O2 in KHCO3 and subsequently reduces to Mn-modified metallic Bi under cathodic potentials. The undoped Bi2O3 is found to follow the same phase transitions but at a different rate. The DFT analyzes the impact of doping the Bi(012) with Mn and indicates significantly improved selectivity for formate generation. Further, the importance of the substrate's hydrophobicity for long-term stability is demonstrated. This study offers in-depth insights into the design and understanding of doped BiOx-based electrodes for CO2 reduction.
Supervalent doping and its effect on the thermal, structural and electrochemical properties of Li7La3Zr2O12 solid electrolytes
(2024-06-21) Košir, Janez; Mousavihashemi, Seyedabolfazl; Suominen, Milla; Kobets, Anna; Wilson, Benjamin P.; Rautama, Eeva-Leena; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Supervalent doping is one of the most common methods used to stabilize the highly conductive cubic phase of Li7La3Zr2O12 (LLZO) solid electrolytes. While several different doping elements have shown that they are capable of stabilizing the cubic LLZO structure, there is still no clear consensus as to an optimal doping strategy. In this study we present one of the most extensive comparative analyses on supervalent doping of LLZO done to date. Herein, we compare the effects of eight different doping elements (Al, Ga, Fe, Ta, Nb, Sb, W and Mo) on the synthesis, crystal structure, morphology, and electrochemical properties of LLZO. We also propose a new guideline that would allow for the quick and easy identification of doping elements in LLZO and the estimation of their concentration using Raman spectroscopy. Our results show how Ga doping leads to exceptionally high ionic conductivities (1.30 × 10−3 S cm−1) and low activation energies (0.26 eV) due to changes in the crystal symmetry of LLZO. On top of that, Ga doping also significantly lowers the required synthesis temperatures and increases the relative density of the LLZO structure, making Ga the most suitable element for LLZO doping. On the other hand, Nb doping shows the lowest ionic conductivity (1.91 × 10−4 S cm−1) and a high activation energy (0.44 eV) of the investigated dopants, due to a poor sintering performance.
Temperature dependent product distribution of electrochemical CO2 reduction on CoTPP/MWCNT Composite
(2022-05) Hossain, Md Noor; Prslja, Paulina; Flox, Cristina; Muthuswamy, Navaneethan; Sainio, Jani; Kannan, A. M.; Suominen, Milla; Lopez, N.; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Electrochemical reduction of CO2 to valuable products on molecular catalysts draws attention due to their versatile structures allowing tuning of activity and selectivity. Here, we investigate temperature influence on CO2 conversion product selectivity over a Cobalt(II)-tetraphenyl porphyrin (CoTPP)/multiwalled carbon nanotube (MWCNT) composite in the range of 20-50℃. Faradaic efficiency of products changes with temperature and potential so that two-electron transfer product CO formation is enhanced at low potentials and temperatures while the competing hydrogen formation shows an opposite trend. Multi-electron transfer product methanol formation is more favorable at low temperatures and potentials whereas reverse applies for methane. Activity and selectivity are analyzed with DFT simulations identifying the key differences between the binding energies of CH2O and CHOH, the binding strength of CO, and the protonation of CHO intermediate. This novel experimental and theoretical understanding for CO2 reduction provides insight in the influence of the various conditions on the product distribution.
Temperature-Controlled Syngas Production via Electrochemical CO2 Reduction on a CoTPP/MWCNT Composite in a Flow Cell
(2023-01-09) Hossain, Md Noor; Khakpour, Reza; Busch, Michael; Suominen, Milla; Laasonen, Kari; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The mixture of CO and H2, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO2 and H2O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO2 and H2O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20–50 °C. The experimental results show that for all the applied potentials the ratio of H2/CO increases with increasing temperature. Interestingly, at −0.6 VRHE and 40 °C, the H2/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at −1.0 VRHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pKa value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.
What We Currently Know about Carbon-Supported Metal and Metal Oxide Nanomaterials in Electrochemical CO2 Reduction
(2021-07-01) Suominen, Milla; Kallio, Tanja
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
Electrochemical reduction of CO2 is considered important in enhancing the circular-economy design; it can suppress harmful greenhouse-gas emissions while, combined with intermittent renewable energy sources, it can employ the surplus energy for production of important chemicals and fuels. In the process, electrocatalysts play an important role as the mediators of the highly active and selective conversion of CO2. Transition and post transition metals and their oxides are an important electrocatalyst group. For practical reasons, these metals need to be applied as nanoparticles supported on highly conducting materials enabling fabrication of 3D electrodes. In this minireview, we focus on gathering our current knowledge on the effects which transition and post transition metal and metal oxide nanoparticles supported on different carbons may have on electrochemical reduction of CO2. We focus on literature of studies conducted in aqueous conditions, under as similar conditions as possible, to ensure comparability. This approach enables us to highlight possible support effects and issues that complicate making conclusions on support effects.