Morphology Changes of Cu₂O Catalysts During Nitrate Electroreduction to Ammonia**

This manuscript reports the electrosynthesis of ammonia from nitrate catalysed Cu derived from Cu2O materials. Cu2O (111) and (100) preferential grain orientations were prepared through electrodeposition. Cu derived from Cu2O (111) is more active and selective for ammonia formation than Cu2O (100) derived Cu. The highest faradaic efficiency (FE) was achieved for both catalysts at −0.3 V vs RHE, with Cu derived from Cu2O (111) reaching up to 80 %. Additional measurements with quasi-in situ X-ray photoelectron spectroscopy and in situ Raman spectroscopy revealed that Cu0 is the active phase during the reaction. The stability of the catalysts was examined by ex situ methods such as SEM, XRD and ICP elemental analysis. The catalysts underwent severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After 3 hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The FE after 3 hours remained higher for the Cu derived from Cu2O (111), suggesting that the activity is dependent on the initial structure and the different rates of dissolution and re-deposition.</p

Hydrogen Evolution Electrocatalysis with a Molecular Cobalt Bis(alkylimidazole)methane Complex in DMF: a Critical Activity Analysis

[Co(HBMIMPh2)2](BF4)2 (1) [HBMIMPh2=bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane] was investigated for its electrocatalytic hydrogen evolution performance in DMF using voltammetry and during controlled potential/current electrolysis (CPE/CCE) in a novel in-line product detection setup. Performances were benchmarked against three reported molecular cobalt hydrogen evolution reaction (HER) electrocatalysts, [Co(dmgBF2)2(solv)2] (2) (dmgBF2=difluoroboryldimethylglyoximato), [Co(TPP)] (3) (TPP=5,10,15,20-tetraphenylporphyrinato), and [Co(bapbpy)Cl](Cl) (4) [bapbpy=6,6′-bis-(2-aminopyridyl)-2,2′-bipyridine], showing distinct performances differences with 1 being the runner up in H2 evolution during CPE and the best catalyst in terms of overpotential and Faradaic efficiency during CCE. After bulk electrolysis, for all of the complexes, a deposit on the glassy carbon electrode was observed, and post-electrolysis X-ray photoelectron spectroscopy (XPS) analysis of the deposit formed from 1 demonstrated only a minor cobalt contribution (0.23 %), mainly consisting of Co2+. Rinse tests on the deposits derived from 1 and 2 showed that the initially observed distinct activity was (partly) preserved for the deposits. These observations indicate that the molecular design of the complexes dictates the features of the formed deposit and therewith the observed activity

Stability of In2O3 Nanoparticles in PTFEcontaining Gas Diffusion Electrodes for CO2 electroreduction to Formate

Electrocatalytic conversion of CO2 to fuels and chemicals can help mitigate climate change by reuse of the greenhouse gas. Formic acid is an interesting product of electrochemical CO2 reduction, because it can serve as a liquid hydrogen carrier. Indium-based electrodes show promising activity and selectivity towards formic acid formation during CO2 electroreduction. However, the low stability of such electrodes at high current density limits their implementation in industry. Herein, we optimize a gas diffusion electrode (GDE) containing ∼6 nm In2O3 nanoparticles obtained by flame spray pyrolysis. The catalyst exhibits high initial faradaic efficiency towards formate (> 80%) at current densities up to 200 mA/cm2. In situ Raman spectroscopy reveals that the In2O3 particles rapidly reduce under reaction conditions, demonstrating that metallic indium is the active phase for CO2 reduction. Degradation mechanisms of the catalyst during 50 h at high current density were studied using XPS, in situ Raman, TEM and SEM, and elemental analysis of the electrolyte. Catalyst reduction, sintering of the active phase and dissolution of indium could be excluded as a cause of the declining FE. Adding carbon and hydrophobic PTFE particles to the catalyst in the GDE improves CO2 supply and prevents early saturation of the GDE by liquid electrolyte. The optimized GDE configuration inhibits hydrogen evolution and demonstrates increased stability during 50 h of CO2 electroreduction

Fuelling the hydrogen economy: Scale-up of an integrated formic acid-to-power system

Transitioning from fossil fuels to sustainable and green energy sources in mobile applications is a difficult challenge and demands sustained and highly multidisciplinary efforts in R&amp;D. Liquid organic hydrogen carriers (LOHC) offer several advantages over more conventional energy storage solutions, but have not been yet demonstrated at scale. Herein we describe the development of an integrated and compact 25 kW formic acid-to-power system by a team of BSc and MSc students. We highlight a number of key engineering challenges encountered during scale-up of the technology and discuss several aspects commonly overlooked by academic researchers. Conclusively, we provide a critical outlook and suggest a number of developmental areas currently inhibiting further implementation of the technology.ChemE/Inorganic Systems EngineeringChemE/Algemee

Nitrate electrochemical reduction to ammonia on Cu2O catalysts

This manuscript reports the electrosynthesis of ammonia from nitrate catalysed by Cu2O. Cu2O (111) and (100) preferential orientations were prepared through electrodeposition to investigate the effect of surface structure. Cu2O (111) is more active and selective for ammonia formation than Cu2O (100). The highest faradaic efficiency (FE) was achieved for both catalysts at -0.3 V vs RHE, with Cu2O (111) reaching up to 80%. Additional measurements with quasi-in situ X-ray photoelectron spectroscopy and in-situ Raman spectroscopy revealed that Cu0 is the active phase during the reaction. The stability of the catalysts was examined by ex-situ methods such as scanning electron microscopy, X-ray diffraction and inductively coupled plasma-optical emission spectrometry. The catalysts undergo severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After three hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The final FE was still higher for the original Cu2O (111) electrode

Hydrogen Evolution Electrocatalysis with a Molecular Cobalt Bis(alkylimidazole)methane Complex in DMF: a critical activity analysis

Abstract: [Co(HBMIMPh2)2](BF4)2 (1), (HBMIMPh2 = bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane), was investigated for its electrocatalytic hydrogen evolution performance in DMF using voltammetry and during controlled potential/current electrolysis (CPE/CCE) in a novel in-line product detection setup. Performances were benchmarked against three reported molecular cobalt HER electrocatalysts: [Co(dmgBF2)2(solv)2] (2), (dmgBF2 = difluoroboryldimethylglyoximato), [Co(TPP)] (3), (TPP = 5,10,15,20-tetraphenylporphyrinato) and [Co(bapbpy)Cl](Cl) (4), (bapbpy = 6,6’-bis-(2-aminopyridyl)-2,2’-bipyridine) showing distinct performances differences with 1 being the runner up in H2 evolution during CPE and the best catalyst in terms of overpotential and FE during CCE. After bulk electrolysis with all of the complexes a deposit on the glassy carbon electrode was observed and post electrolysis XPS analysis of the deposit formed from 1 demonstrated only a minor cobalt contribution (0.23%), mainly consisting of Co2+. Rinse tests on the deposits derived from 1 and 2 showed that the initially observed distinct activity is (partly) preserved for the deposits. These observations indicate that the molecular design of the complexes dictates the features of the formed deposit and therewith the observed activity

Evolution of bismuth oxide catalysts during electrochemical CO₂ reduction

Bismuth is a promising electrocatalyst for active and selective CO2 electroreduction to formate. Herein, we investigated the evolution of various Bi-based catalysts (β-Bi2O3 nanoparticles, BiOBr nanosheets, Bi2O2CO3 nanosheets, and large α-Bi2O3 and β-Bi2O3 particles) during reaction. Apart from the α-Bi2O3 particles, all the electrocatalysts reach the same Faradaic efficiency (93 ± 2%) and current density during potentiostatic operation, and their morphology changed to nanosheets. This change in morphology can be linked to the formation of Bi2O2CO3 layers, which are prone to reduction to metallic Bi. The final phase and morphology depend on the size of the Bi precursor. Quasi-in situ XPS suggests that a Bi2O2CO3 contribution persists on the surface even for the reduced catalysts. At a current density of 200 mA/cm2, all catalysts reduce to metallic Bi without forming a well-defined sheet morphology. Only for the Bi2O3 nanoparticles can a FE above 90% be maintained.</p

Electrochemical CO2 Reduction on Gas Diffusion Electrodes: Enhanced Selectivity of In-Bi Bimetallic Particles and Catalyst Layer Optimization through a Design of Experiment Approach

CO2 electroreduction to formate powered by renewable energy is an attractive strategy to recycle carbon. Electrode materials showing high selectivity for formate at high current densities are post-transition metals such as Sn, In, Pb, Hg, and Bi. Scaling up the CO2 electroreduction technology to industrial size will require, among other things, maximization of selectivity at high current densities. We show here that InBi electrocatalysts provide enhanced selectivity compared to pure In and Bi and that a proper formulation of the catalyst layer can have a profound impact on the performance of gas diffusion electrode electrolyzers. The best performing electrodes screened in this study show nearly 100% current efficiency at current densities up to 400 mA cm-2 for 2 h. Additionally, one electrode was shown to operate at a current density of 200 mA cm-2 for 48 h at a current efficiency of 85% and remained operating with a current efficiency above 50% for 124 h