Publisher Correction: Copper adparticle enabled selective electrosynthesis of n-propanol.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

System-based Approaches for the Enhancement of Catalytic CO2 Reduction Reactions

This thesis focusses on the importance of system design, specifically the engineering of gas, liquid and solid catalyst interactions, in enhancing catalytic CO2 reduction processes. The most impactful contributions of this thesis are: the enhancement of CO2 production rates via morphology-induced mass transport (Chapter 3); the manipulation of local reaction environments to increase electrochemical CO2-to-ethylene production in an H-cell configuration (Chapter 4); the design of an abrupt reaction interface adjacent to a gas-liquid interface for high current and selective ethylene production in an alkaline media (Chapter 5); and the creation of a scalable multi-phase photocatalytic reactor (Chapter 6). While material science and chemistry are essential in the creation and functionality of CO2 reduction catalysts, the overall system surrounding the solid catalyst plays a similar influential role in determining the overall efficiency, product distribution and production rate. By understanding the complex interactions between a solid catalyst, liquid electrolyte and gas reagents/products, the underlying influences of system engineering on catalyst performance can be extracted and improved. Using this approach catalyst surface morphology is revealed to increase limiting current densities multifold by enhancing the natural mass transport effects of departing CO2 reduction products. The pH and CO2 gradients formed at the catalystâ s surface during the reaction similarly influence product selectivity, most notably the ratio between hydrogen, methane and ethylene using copper-based catalysts. Equipped with this understanding, tuning catalyst morphology under differing buffering capacities allowed for traditionally coupled CO2 limitations and electrode pH to become partially decoupled; ethylene production under ambient conditions then improved significantly as compared to a catalytic system void of such considerations. Expanding on this knowledge CO2 reduction catalysts were designed to operate in a highly alkaline environment where the reaction onset potential for ethylene formation was found to be reduced to unparalleled levels. The system design, which manipulated a sub-100 nm diffusion interface, similarly led to half-cell power conversion efficiencies higher than previous efforts at significantly improved production rates.Ph.D.2018-12-19 00:00:0

Enhancing Electrocatalytic CO2 Reduction Using a System-Integrated Approach to Catalyst Discovery

The presented modelling results in this article show that electrochemical CO2 reduction performed at commercially-relevant current densities will ultimately lead to locally alkaline reaction conditions regardless of the electrolyte, configuration and reasonable mass transport scenarios. Discussed in detail are the large implications that this result has for the CO2 reduction reaction itself, and the current way in which catalysts are designed and tested in different electrochemical cell architectures

Spatial reactant distribution in CO2 electrolysis: Balancing CO2 utilization and Faradaic Efficiency

The production of value added C1 and C2 compounds within CO2 electrolyzers has reached sufficient catalytic performance that system and process performance – such as CO2 utilization – have come more into consideration. Efforts to assess the limitations of CO2 conversion and crossover within electrochemical systems have been performed, providing valuable information to position CO2 electrolyzers within a larger process. Currently missing, however, is a clear elucidation of the inevitable trade-offs that exist between CO2 utilization and electrolyzer performance, specifically how the Faradaic Efficiency of a system varies with CO2 availability. Such information is needed to properly assess the viability of the technology. In this work, we provide a combined experimental and 3D modelling assessment of the trade-offs between CO2 utilization and selectivity at 200 mA/cm2 within a membrane-electrode assembly CO2 electrolyzer. Using varying inlet flow rates we demonstrate that the variation in spatial concentration of CO2 leads to spatial variations in Faradaic Efficiency that cannot be captured using common ‘black box’ measurement procedures. Specifically, losses of Faradaic efficiency are observed to occur even at incomplete CO2 consumption (80%). Modelling of the gas channel and diffusion layers indicated at least a portion of the H2 generated is considered as avoidable by proper flow field design and modification. The combined work allows for a spatially resolved interpretation of product selectivity occurring inside the reactor, providing the foundation for design rules in balancing CO2 utilization and device performance in both lab and scaled applications

Visualization of spatial electrochemical activity via a combined thermal-electric potentiostat

The electrolysis of water, CO2 and N2 provide options for producing fossil-free fuels and feedstocks at global scales. Technological advancements are challenged by the complexity of phenomena spanning broad physical scales (angstroms to meters) and scientific domains. Further, activity is presently quantified indirectly, hindering disambiguation of catalytic and system effects. Here, we present a spatial thermal-electric potentiostat (STEP) which links local electrochemical activity to an associated operando heat signature. The STEP then directly maps catalytic activity with fine resolutions in temperature (10 mK), time (0.2 s) and space (0.1 mm), capturing operational phenomena as they occur. We demonstrate STEP’s potential for catalyst screening, degradation measurements and spatial mapping through water and CO2 electrolysis experiments up to 0.2 A cm-2. We identify rapid catalytic temperature spikes with activity (>10 K at 0.2 A cm-2) and localized activity fluctuations in operation, both which challenge many perceptions of the electrocatalyst and reaction environment during operation

Introductory Guide to Assembling and Operating Gas Diffusion Electrodes for Electrochemical CO ₂ Reduction

ChemE/Materials for Energy Conversion & Storag

A penalty on photosynthetic growth in fluctuating light

Fluctuating light is the norm for photosynthetic organisms, with a wide range of frequencies (0.00001 to 10 Hz) owing to diurnal cycles, cloud cover, canopy shifting and mixing; with broad implications for climate change, agriculture and bioproduct production. Photosynthetic growth in fluctuating light is generally considered to improve with increasing fluctuation frequency. Here we demonstrate that the regulation of photosynthesis imposes a penalty on growth in fluctuating light for frequencies in the range of 0.01 to 0.1 Hz (organisms studied: Synechococcus elongatus and Chlamydomonas reinhardtii). We provide a comprehensive sweep of frequencies and duty cycles. In addition, we develop a 2nd order model that identifies the source of the penalty to be the regulation of the Calvin cycle - present at all frequencies but compensated at high frequencies by slow kinetics of RuBisCO.Tis work was supported through a Strategic Grant from the Natural Science and Engineering Research Council of Canada, the University of Toronto Connaught Global Scholars Program in Bio-Inspired Ideas for Sustainable Energy, the University of Toronto McLean Senior Fellowship (DS), E.W.R. Steacie Memorial Fellowship (D.S.), and the Canada Research Chairs Program. P.G. gratefully acknowledges NSERC PGS and Hatch Scholarships. B.N. gratefully acknowledges funding from Ontario Graduate Scholarships, the Queen Elizabeth II Graduate Scholarships in Science & Technology and the MEET, NSERC CREATE Program. T.B. is thankful for support from the NSERC PGS program. Ongoing infrastructure support from the Canadian Foundation for Innovation and operational support through the NSERC Discovery Program is also gratefully acknowledged. Plate reading and preparation equipment used in this study was provided by Te 3D (Diet, Digestive Tract and Disease) Centre funded by the Canadian Foundation for Innovation and Ontario Research Fund, project number 19442 and 30961

Modeling the Electrical Double Layer to Understand the Reaction Environment in a CO2 Electrocatalytic System

The environment of a CO2 electroreduction (CO2ER) catalyst is intimately coupled with the surface reaction energetics and is therefore a critical aspect of the overall system performance. The immediate reaction environment of the electrocatalyst constitutes the electrical double layer (EDL) which extends a few nanometers into the electrolyte and screens the surface charge density. In this study, we resolve the species concentrations and potential profiles in the EDL of a CO2ER system by self-consistently solving the migration, diffusion and reaction phenomena using the generalized modified Poisson-Nernst-Planck (GMPNP) equations which include the effect of volume exclusion due to the solvated size of solution species. We demonstrate that the concentration of solvated cations builds at the outer Helmholtz plane (OHP) with increasing applied potential until the steric limit is reached. The formation of the EDL is expected to have important consequences for the transport of the CO2 molecule to the catalyst surface. The electric field in the EDL diminishes the pH in the first 5 nm from the OHP, with an accumulation of protons and a concomitant depletion of hydroxide ions. This is a considerable departure from the results obtained using reaction-diffusion models where migration is ignored. Finally, we use the GMPNP model to compare the nature of the EDL for different alkali metal cations to show the effect of solvated size and polarization of water on the resultant electric field. Our results establish the significance of the EDL and electrostatic forces in defining the local reaction environment of CO2 electrocatalysts.</p

Mass Transport in Catalytic Pores of GDE-Based CO2 Electroreduction Systems

Gas diffusion electrode (GDE)-based setups have shown promising performance for CO2 electrocatalysis and further development of these systems will be important on the path to industrial feasibility. In this article, we model an effective catalyst pore within a GDE-based flow-cell to study the influence of the catalyst structure and operating conditions on the reaction environment for CO2 electrocatalysis at practically relevant current densities. Using a generalized modified Poisson-Nernst-Planck (GMPNP) 3D model of the nanoporous catalyst layer, we show that the length of the catalyst pore as well as the boundary conditions at the gas-electrolyte and electrolyte-electrolyte interfaces across this length are highly influential parameters for determining the conditions within the catalyst pore. Pores with the same catalytic surface area can have very different reaction environments depending primarily on the pore length and not the pore radius. Properties such as electrolyte pH and buffer breakdown, ionic strength and CO2 concentration are also highly-sensitive to the catalyst layer thickness, gas pressure, electrolyte flow rate and the flow-channel geometry. The applied potential impacts the concentration of ionic species in the pore, which in turn determines the solubility of CO2 available for the reaction. Our results underline the need to understand and manage transport within GDE-based electrocatalysis systems as an essential means to control catalyst performance. Benchmarking of GDE-based electrocatalytic systems against their structural and operational parameters will be important for achieving improvements in performance that can be ultimately translated to large-scale operation