Mn3O4@CoMn2O4-CoxOy nanoparticles : partial cation exchange synthesis and electrocatalytic properties toward the oxygen reduction and evolution reactions

Mn3O4@CoMn2O4 nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one -pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn3O4 NPs. Selecting the proper cobalt precursor, the nucleation of CoxOy crystallites at the Mn3O4@a CoMn2O4 surface could be simultaneously promoted to form Mn3O4@CoMn2O4-CoxOy NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn3O4@ CoMn2O4-Cox0y NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 Vat(-3) mA.cm(-2) and a small Tafel slope of 52 mV.dec(-1) for ORR, and overpotentials of 0.31 V at 10 mAPeer ReviewedPostprint (author's final draft

Production of Solar Fuels by Photoelectrochemical Conversion of Carbon Dioxide

[eng] Growing global emission of carbon dioxide gas (CO2) reflects the world’s energy dependence on fossil fuels. The conversion of CO2 emission into value-added products, like fuels completes a circular CO2 economy which requires a renewable energy conversion and storage system. Amongst a few, photo/electrochemistry has been particularly appealing thanks to its energy efficiency and enormous potential for industrial applications. Formic acid (HCOOH) production from CO2 reduction appears as an alternative energy storage option based on the commercialization of this process. Herein, stable and selective catalysts working at low overpotential are needed to reduce CO2. Likewise, cell design is critical to have improved CO2 mass transport for obtaining high conversion efficiencies and to achieve feasible production yields. The initial work was conducted on the design and understanding of operational parameters of an electrochemical flow cell (ECf-cell) such as flow rates and electrode potentials. For CO2 reduction at the cathode site, two different gas diffusion electrodes were produced by electrodeposition: Sn-GDE and Cu-GDE. An optimum potential range was established to control HCOOH selectivity. The complementing reaction at the anode site, oxygen evolution reaction (OER), was studied using Mn-Co oxide nanoparticles to replace expensive DSA: Ir-Ta oxide catalyst. Subsequent efforts were devoted on the assembly of a photoelectrochemical flow cell (PECf-cell) which enabled coupling of Sn-GDE as cathode vs. TiO2 nanorods as photoanode. This led to nearly 1/3 reduction in overall cell voltage reaching an energy efficiency up to 70 %. The solar-to-fuel (STF) conversion efficiency was 0.25% which was one of the highest efficiencies reported amongst the data obtained from a cell in device level. The results proved that optimized system efficiency could be achieved with a large bandgap photoanode having superior stability and a GDE cathode with improved CO2 mass transfer. The deployment of renewable energy sources will require new technologies to emerge. The photoelectrochemical flow cell developed in this work can store energy from intermittent electricity sources (i.e. wind and solar) in a sustainable manner. This may pave the way for commercialization of this process and moving towards a circular CO2 economy.[spa] La conversión de CO2 en productos de valor añadido con energías renovables resulta interesante para mitigar las emisiones de este. La conversión foto/electroquímica es atractiva por su eficiencia energética y su enorme potencial para aplicaciones industriales. La producción de ácido fórmico (HCOOH) a partir de la reducción de CO2 aparece como una vía alternativa para su comercialización. Sin embargo, se requieren catalizadores estables y selectivos que trabajen a bajo sobre potencial. Además, el diseño de la celda es crítico para mejorar el transporte de masa de CO2 y obtener elevadas eficiencias de conversión. En este trabajo se estudió en un primer lugar el diseño y la comprensión de los parámetros operativos de una celda de flujo electroquímica: caudales y potenciales de electrodo. Para la reducción de CO2 sobre el cátodo, se emplearon dos electrodos diferentes de difusión de gas preparados por electrodeposición: Sn-GDE y Cu-GDE. Se estableció un valor de operación óptimo para controlar la selectividad a HCOOH. Se estudió también la reacción complementaria en el ánodo (evolución de O2), empleando nanopartículas de óxido de Mn-Co para reemplazar el elevado coste del catalizador de óxido de Ir-Ta. Finalmente, se montó una celda fotoelectroquímica de flujo que permitió la inclusión de TiO2 nanorods como fotoánodo. El voltaje total de la celda se redujo alrededor 1/3 alcanzando una eficiencia energética del 70 %. El rendimiento de conversión de energía solar a combustible (STF) fue de 0,25%. Los resultados demuestran que se puede lograr una eficiencia optimizada del sistema con un fotoánodo que tiene una buena estabilidad y un cátodo que favorece la transferencia de masa de CO2. La celda de flujo fotoelectroquímica desarrollada en este trabajo permite almacenar energía de fuentes de electricidad intermitentes (eólica y/o solar) de una manera sostenible, con el consiguiente avance en una economía circular de CO2

Energy comparison of sequential and integrated CO2 capture and electrochemical conversion

Integrating carbon dioxide (CO2) electrolysis with CO2 capture provides exciting new opportunities for energy reductions by simultaneously removing the energy-demanding regeneration step in CO2 capture and avoiding critical issues faced by CO2 gas-fed electrolysers. However, understanding the potential energy advantages of an integrated process is not straightforward due to the interconnected processes which require knowledge of both capture and electrochemical conversion processes. Here, we identify the upper limits of the integrated process from an energy perspective by comparing the working principles and performance of integrated and sequential approaches. Our high-level energy analyses unveil that an integrated electrolyser must show similar performance to the gas-fed electrolyser to ensure an energy benefit of up to 44% versus the sequential route. However, such energy benefits diminish if future gas-fed electrolysers resolve the CO2 utilisation issue and if an integrated electrolyser shows lower conversion efficiencies than the gas-fed system

Ligand-mode directed selectivity in Cu-Ag core-shell based gas diffusion electrodes for CO2 electroreduction

Bimetallic nanoparticles with tailored size and specific composition have shown promise as stable and selective catalysts for electrochemical reduction of CO2 (CO2R) in batch systems. Yet, limited effort was devoted to understand the effect of ligand coverage and postsynthesis treatments on CO2 reduction, especially under industrially applicable conditions, such as at high currents (>100 mA/cm2) using gas diffusion electrodes (GDE) and flow reactors. In this work, Cu–Ag core–shell nanoparticles (11 ± 2 nm) were prepared with three different surface modes: (i) capped with oleylamine, (ii) capped with monoisopropylamine, and (iii) surfactant-free with a reducing borohydride agent; Cu–Ag (OAm), Cu–Ag (MIPA), and Cu–Ag (NaBH4), respectively. The ligand exchange and removal was evidenced by infrared spectroscopy (ATR-FTIR) analysis, whereas high-resolution scanning transmission electron microscopy (HAADF-STEM) showed their effect on the interparticle distance and nanoparticle rearrangement. Later on, we developed a process-on-substrate method to track these effects on CO2R. Cu–Ag (OAm) gave a lower on-set potential for hydrocarbon production, whereas Cu–Ag (MIPA) and Cu–Ag (NaBH4) promoted syngas production. The electrochemical impedance and surface area analysis on the well-controlled electrodes showed gradual increases in the electrical conductivity and active surface area after each surface treatment. We found that the increasing amount of the triple phase boundaries (the meeting point for the electron–electrolyte–CO2 reactant) affect the required electrode potential and eventually the C+2e̅/C2e̅ product ratio. This study highlights the importance of the electron transfer to those active sites affected by the capping agents—particularly on larger substrates that are crucial for their industrial application

Mn₃O₄@CoMn₂O₄-CoₓOy nanoparticles : Partial cation exchange synthesis and electrocatalytic properties toward the oxygen reduction and evolution reactions

Mn₃O₄@CoMn₂O₄ nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one-pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn₃O₄ NPs. Selecting the proper cobalt precursor, the nucleation of CoₓOy crystallites at the Mn₃O₄@CoMn₂O₄ surface could be simultaneously promoted to form Mn₃O₄@CoMn₂O₄-CoₓOy NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn₃O₄@CoMn₂O₄-CoₓOy NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 V at −3 mA·cm-2 and a small Tafel slope of 52 mV·dec-1 for ORR, and overpotentials of 0.31 V at 10 mA·cm-2 and a Tafel slope of 81 mV·dec-1 for OER, thus outperforming commercial Pt-, IrO2-based and previously reported transition metal oxides. This cation-exchange-based synthesis protocol opens up a new approach to design novel heterostructured NPs as efficient nonprecious metal bifunctional oxygen catalysts

Mn3O4@CoMn2O4-CoxOy nanoparticles : partial cation exchange synthesis and electrocatalytic properties toward the oxygen reduction and evolution reactions

Mn3O4@CoMn2O4 nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one -pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn3O4 NPs. Selecting the proper cobalt precursor, the nucleation of CoxOy crystallites at the Mn3O4@a CoMn2O4 surface could be simultaneously promoted to form Mn3O4@CoMn2O4-CoxOy NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn3O4@ CoMn2O4-Cox0y NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 Vat(-3) mA.cm(-2) and a small Tafel slope of 52 mV.dec(-1) for ORR, and overpotentials of 0.31 V at 10 mAPeer Reviewe