Browsing by Author "Andronescu, Corina"
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Item B-Cu-Zn Gas Diffusion Electrodes for CO2 Electroreduction to C2+ Products at High Current Densities(Angewandte Chemie International Edition, 2021) Song, Yanfang; Junqueira, Jo¼o R. C.; Sikdar, Nivedita; Masa, Justus; Andronescu, Corina; Schuhmann, WolfgangElectroreduction of CO2 to multi-carbon products has attracted considerable attention as it provides an avenue to high-density renewable energy storage. However, the selectivity and stability under high current densities are rarely reported. Herein, B-doped Cu (B-Cu) and B-Cu-Zn gas diffusion electrodes (GDE) were developed for highly selective and stable CO2 conversion to C2+ products at industrially relevant current densities. The B-Cu GDE exhibited a high Faradaic efficiency of 79 % for C2+ products formation at a current density of −200 mA cm−2 and a potential of −0.45 V vs. RHE. The long-term stability for C2+ formation was substantially improved by incorporating an optimal amount of Zn. Operando Raman spectra confirm the retained Cu+ species under CO2 reduction conditions and the lower overpotential for *OCO formation upon incorporation of Zn, which lead to the excellent conversion of CO2 to C2+ products on B-Cu-Zn GDEs.Item Combining Nanoconfinement in Ag Core/Porous Cu Shell Nanoparticles with Gas Diffusion Electrodes for Improved Electrocatalytic Carbon Dioxide Reduction(ChemElectroChem, 2021) Junqueira, João R. C.; O’Mara, Peter B.; Wilde, Patrick; Dieckhöfer, Stefan; Benedetti, Tania M.; Andronescu, Corina; Tilley, Richard D.; Gooding, J. Justin; Schuhmann, WolfgangBimetallic silver-copper electrocatalysts are promising materials for electrochemical CO2 reduction reaction (CO2RR) to fuels and multi-carbon molecules. Here, we combine Ag core/porous Cu shell particles, which entrap reaction intermediates and thus facilitate the formation of C2+ products at low overpotentials, with gas diffusion electrodes (GDE). Mass transport plays a crucial role in the product selectivity in CO2RR. Conventional Hcell configurations suffer from limited CO2 diffusion to the reaction zone, thus decreasing the rate of the CO2RR. In contrast, in the case of GDE-based cells, the CO2RR takes place under enhanced mass transport conditions. Hence, investigation of the Ag core/porous Cu shell particles at the same potentials under different mass transport regimes reveals: (i) a variation of product distribution including C3 products, and (ii) a significant change in the local OH- activity under operation.Item Electrocatalysis as the Nexus for Sustainable Renewable Energy: The Gordian Knot of Activity, Stability, and Selectivity(Angewandte Chemie International Edition, 2020) Masa, Justus; Andronescu, Corina; Schuhmann, WolfgangThe use of renewable energy by means of electrochemical techniques by converting H2O, CO2 and N2 into chemical energy sources and raw materials, is the basis for securing a future sustainable “green” energy supply. Some weaknesses and inconsistencies in the practice of determining the electrocatalytic performance, which prevents a rational bottom-up catalyst design, are discussed. Large discrepancies in material properties as well as in electrocatalytic activity and stability become obvious when materials are tested under the conditions of their intended use as opposed to the usual laboratory conditions. They advocate for uniform activity/stability correlations under application-relevant conditions, and the need for a clear representation of electrocatalytic performance by contextualization in terms of functional investigation or progress towards application is emphasized.Item Influence of Temperature and Electrolyte Concentration on the Structure and Catalytic Oxygen Evolution Activity of NiFe LDH(Chemistry–A European Journal, 2018) Andronescu, Corina; Seisel, Sabine; Wilde, Patrick; Barwe, Stefan; Masa, Justus; Schuhmann, WolfgangNiFe layered double hydroxide (LDH) is inarguably the most active contemporary catalyst for the oxygen evolution reaction under alkaline conditions. However, the ability to sustain unattenuated performance under challenging industrial conditions entailing high corrosivity of the electrolyte (≈30 wt. % KOH), high temperature (>80 °C) and high current densities (>500 mA cm−2) is the ultimate criterion for practical viability. This work evaluates the chemical and structural stability of NiFe LDH at conditions akin to practical electrolysis, in 30 % KOH at 80 °C, however, without electrochemical polarization, and the resulting impact on the OER performance of the catalyst. Post-analysis of the catalyst by means of XRD, TEM, FT-IR, and Raman spectroscopy after its immersion into 7.5 m KOH at 80 °C for 60 h revealed a transformation of the structure from NiFe LDH to a mixture of crystalline β-Ni(OH)2 and discrete predominantly amorphous FeOOH containing minor non-homogeneously distributed crystalline domains. These structural and compositional changes led to a drastic loss of the OER activity. It is therefore recommended to study catalyst stability at industrially relevant conditions.Item Is Cu instability during the CO2 reduction reaction governed by the applied potential or the local CO concentration?(Chemical science, 2021) Wilde, Patrick; O'Mara, Peter B.; Junqueira, Joao R. C.; Tarnev, Tsvetan; Benedetti, Tania M.; Andronescu, Corina; Chen, Yen-Ting; Tilley, Richard D.; Schuhmann, Wolfgang; Gooding, J. Justinhave shown structural instability during the electrochemical CO2 reduction reaction (CO2RR). However, studies on monometallic Cu catalysts do not allow a nuanced differentiation between the contribution of the applied potential and the local concentration of CO as the reaction intermediate since both are inevitably linked. We first use bimetallic Ag-core/porous Cu-shell nanoparticles, which utilise nanoconfinement to generate high local CO concentrations at the Ag core at potentials at wItem Low Overpotential Water Splitting Using Cobalt-Cobalt Phosphide (Co/Co2 P) Nanoparticles Supported on Nickel Foam(ACS Energy Letters, 2016) Masa, Justus; Barwe, Stefan; Andronescu, Corina; Ruff, Adrian; Jayaramulu, Kolleboyina; Elumeeva, KarinaWe report a simple, facile, and safe route for preparation of cobalt–cobalt phosphide (Co/Co2P) nanoparticles and demonstrate their application as efficient low-cost catalysts for electrochemical water splitting. The catalyst achieves good performance in catalyzing both the cathode and anode half-cell water-splitting reactions in 1.0 M KOH and the hydrogen evolution reaction in an acidic electrolyte, 0.5 M H2SO4. For the oxygen evolution reaction in 1.0 M KOH, a current of 10 mA cm–2 was attained at 0.39 V overpotential on a glassy carbon electrode, while an overpotential of 0.19 V was attained at 50 mA cm–2 when the catalyst was supported on nickel foam.Item MOFs for Electrocatalysis: From Serendipity to Design Strategies(Small Methods, 2019) Aiyappa, Harshitha Barike; Masa, Justus; Andronescu, CorinaThe rapid upsurge of metal–organic frameworks (MOFs) as well as MOF-derived materials has stimulated profound interest to capitalize on their many potential untapped benefits in electrocatalysis for energy applications. The possibility of tuning the metal–ligand junctions of the MOF architecture opens new avenues to design robust, extended heterostructures for addressing the present-day energy challenges. Interestingly, despite having detailed crystallographic information, it is often difficult to envisage the interplay of charge transport (electrons and ions), mass transport (pore system) together with the specific effects of the molecularly defined reaction center of MOFs for a given electrocatalytic reaction. Here, guidelines are offered for judiciously engineering the electronic structure of MOFs to deliver targeted electrocatalytic function. Some of the pivotal works on MOF-based materials for electrocatalysis are discussed, which can be correlated to the biological models in terms of their structural resemblance and an instructive insight is provided about the “new chemistry” that can be explored based on the lessons learned from nature in combination with the theoretical understanding of the energetics of the reactions.Item Oxygen Evolution Electrocatalysis of a Single MOF-derived Composite Nanoparticle on the tip of a Nanoelectrode(Angewandte Chemie International Edition, 2019) Aiyappa, Harshitha Barike; Wilde, Patrick; QuasT, Thomas; Masa, Justus; Andronescu, Corina; Schuhmann, WolfgangDetermination of the intrinsic electrocatalytic activity of nanomaterials by means of macroelectrode techniques is compromised by ensemble and film effects. Here, a unique “particle on a stick” approach is used to grow a single metal–organic framework (MOF; ZIF-67) nanoparticle on a nanoelectrode surface which is pyrolyzed to generate a cobalt/nitrogen-doped carbon (CoN/C) composite nanoparticle that exhibits very high catalytic activity towards the oxygen evolution reaction (OER) with a current density of up to 230 mA cm−2 at 1.77 V (vs. RHE), and a high turnover frequency (TOF) of 29.7 s−1 at 540 mV overpotential. Identical location transmission electron microscopy (IL-TEM) analysis substantiates the “self-sacrificial” template nature of the MOF, while post-electrocatalysis studies reveal agglomeration of Co centers within the CoN/C composite during the OER. “Single-entity” electrochemical analysis allows for deriving the intrinsic electrocatalytic activity and furnishes insight into the transient behavior of the electrocatalyst under reaction conditions.Item Powder Catalyst Fixation for Post-Electrolysis Structural Characterization of NiFe Layered Double Hydroxide Based Oxygen Evolution Reaction Electrocatalysts(Angewandte Chemie International Edition, 2017) Andronescu, Corina; Barwe, Stefan; Ventosa, Edgar; Masa, Justus; Vasile, Eugeniu; Schuhmann, WolfgangAn active and stable OER catalyst was directly fixated on an electrode starting from a NiFe layered double hydroxide (LDH)/polybenzoxazine composite. Owing to its stable immobilization on the electrode, the catalyst can be characterized before and after electrolysis. After electrolysis at 200 mA cm−2 in 5 m KOH for 100 h, previously not reported structural changes were observed for the NiFe LDH.Item Role of Boron and Phosphorus in Enhanced Electrocatalytic Oxygen Evolution by Nickel borides and Nickel Phosphides(ChemElectroChem, 2019) Masa, Justus; Andronescu, Corina; Antoni, Hendrik; Seisel, Sabine; Barwe, Stefan; Roldan, Beatriz CuenyaThe modification of nickel with boron or phosphorus leads to significant enhancement of its electrocatalytic activity for the oxygen evolution reaction (OER). However, the precise role of the guest elements, B and P, in enhancing the OER of the host element (Ni) remains unclear. Herein, we present insight into the role of B and P in enhancing electrocatalysis of oxygen evolution by nickel borides and nickel phosphides. The apparent activation energy, Ea*, of electrocatalytic oxygen evolution on Ni2P was 78.4 kJ/mol, on Ni2B 65.4 kJ/mol, and on Ni nanoparticles 94.0 kJ/mol, thus revealing that both B and P affect the intrinsic activity of nickel. XPS data revealed shifts of −0.30 and 0.40 eV in the binding energy of the Ni 2p3/2 peak of Ni2B and Ni2P, respectively, with respect to that of pure Ni at 852.60 eV, thus indicating that B and P induce opposite electronic effects on the surface electronic structure of Ni. The origin of enhanced activity for oxygen evolution cannot, therefore, be attributed to such electronic modification or ligand effect. Severe changes induced on the nickel lattice, specifically, the Ni-Ni atomic order and interatomic distances (strain effect), by the presence of the guest atoms seem to be the dominant factors responsible for enhanced activity of oxygen evolution in nickel borides and nickel phosphides.