8 Search Results

Sluggish kinetics in the oxygen reduction reaction (ORR) require significant quantities of expensive Pt based nanoparticles on carbon (Pt/C) at the cathode of proton exchange membrane fuel cells (PEMFCs). This catalyst requirement hinders their large-scale implementation. Single atom Fe in N-doped C (Fe–N– C) electrocatalysts offer the best non-Pt-based ORR activities to date, but their environmental impacts have not been studied and their production costs are rarely quantified. Herein, we report a comparative life-cycle assessment and techno-economic analysis of replacing Pt/C with Fe–N–C at the cathode of an 80 kW PEMFC stack. In the baseline scenario (20 g_Pt/C vs. 690more » g_Fe–N–C), we estimate that Fe–N–C could reduce damages on ecosystems and human health by 88–90% and 30–44%, respectively, while still increasing global warming potential by 53–92% and causing a comparable impact on resource depletion. The environmental impacts of Pt/C predominantly arise from the Pt precursor while those of Fe–N–C are presently dominated by the electricity consumption. The monetized costs of environmental externalities for both Fe–N–C and Pt/C catalysts exceed their respective direct production costs. Based on catalyst performance with learning curve analysis at 500 000 PEMFC stacks per annum, we estimate replacing Pt/C with Fe–N–C would increase PEMFC stack cost from 13.8 to 41.6 USD per kW. The cost increases despite a reduction in cathode catalyst production cost from 3.41 to 0.79 USD per kW (excluding environmental externalities). To be cost-competitive with a Pt-based PEMFC stack delivering 2020 US Department of Energy target of 1160 mW cm^-2 (at 0.657 V), the same stack with an Fe–N–C cathode would need to reach 874 mW cm^-2, equivalent to a 200% performance improvement. These findings demonstrate the need for continued Fe–N–C activity development with sustainable synthesis routes in mind to replace Pt based cathode catalyst in PEMFCs. Based on forecasting scenarios of fuel cell vehicle deployment targets, we find that Pt consumption would be constrained by Pt supply.« less

Abstract Electrochemical CO ₂ reduction (CO ₂ R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO ₂ R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application ofmore » data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.« less

Water oxidation is the step limiting the efficiency of electrocatalytic hydrogen production from water. Spectroelectrochemical analyzes are employed to make a direct comparison of water oxidation reaction kinetics between a molecular catalyst, the dimeric iridium catalyst [Ir₂(pyalc)₂(H₂O)₄-(μ-O)]²⁺ (Ir_Molecular, pyalc = 2-(2’pyridinyl)-2-propanolate) immobilized on a mesoporous indium tin oxide (ITO) substrate, with that of an heterogenous electrocatalyst, an amorphous hydrous iridium (IrO_x) film. For both systems, four analogous redox states were detected, with the formation of Ir(4+)-Ir(5+) being the potential-determining step in both cases. However, the two systems exhibit distinct water oxidation reaction kinetics, with potential-independent first-order kinetics for Ir_Molecular contrastingmore » with potential-dependent kinetics for IrO_x. This is attributed to water oxidation on the heterogenous catalyst requiring co-operative effects between neighboring oxidized Ir centers. The ability of Ir_Molecular to drive water oxidation without such co-operative effects is explained by the specific coordination environment around its Ir centers. These distinctions between molecular and heterogenous reaction kinetics are shown to explain the differences observed in their water oxidation electrocatalytic performance under different potential conditions.« less

Understanding the nature of active sites is central to controlling the activity of a given catalyst. This work combines operando characterization and computational techniques to examine the oxygen evolution reaction mechanism on RuO2 surfaces. Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO2 surfaces as a function of voltage. At 1.5 V-RHE, our results suggest that there is an -OO group on the coordinatively unsaturated ruthenium (Ru-CUS) site of the (100) surface (andmore » similarly for (110)), but adsorbed oxygen on the Ru-CUS site of (101). Density functional theory results indicate that the removal of -OO from the Ru-CUS site, which is stabilized by a hydrogen bond to a neighbouring -OH (-OO-H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the Ru-CUS site of (101) resulted in a different rate-determining step (-O + H2O - (H+ + e(-)) -> -OO-H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity.« less

Rutile RuO2 is a highly active catalyst for a number of (electro)chemical reactions in aqueous solutions or in humid environments. However, the study of the interaction of RuO2 surfaces with water has been confined largely to the ultrahigh vacuum environment and to the thermodynamically stable (110) surface. In this work, we combine ambient-pressure X-ray photoelectron spectroscopy, in situ surface diffraction, and density functional theory calculations to investigate how four different facets of RuO2 interact with water under humid and electrochemical environments. The vacant coordinatively unsaturated Ru site (CUS) allows for the adsorption and dissociation of water molecules. Different surfaces exhibitmore » unique binding energetics for -H2O and -OH and can allow for different degrees of hydrogen bonding between the adsorbates. Consequently, the degree of water dissociation is found to be sensitive to the surface crystallographic orientation-being maximum for the (101) surface, followed by the (110), (001) and (100) surfaces. This study identifies crystallographic orientation as an important parameter to tune not only the density of active sites but also the energetics for water dissociation; this finding is of great significance for many catalytic reactions, where water is a key reactant, or product.« less

Oxide-derived copper (OD-Cu) electrodes exhibit unprecedented CO reduction performance towards liquid fuels, producing ethanol and acetate with >50 % Faradaic efficiency at -0.3 V (vs. RHE). By using static headspace-gas chromatography for liquid phase analysis, we identify acetaldehyde as a minor product and key intermediate in the electroreduction of CO to ethanol on OD-Cu electrodes. Acetaldehyde is produced with a Faradaic efficiency of ≈5 % at -0.33 V (vs. RHE). We show that acetaldehyde forms at low steady-state concentrations, and that free acetaldehyde is difficult to detect in alkaline solutions using NMR spectroscopy, requiring alternative methods for detection and quantification.more » Our results indicate an important step towards understanding the CO reduction mechanism on OD-Cu electrodes.« less

Low-temperature fuel cells are limited by the oxygen reduction reaction, and their widespread implementation in automotive vehicles is hindered by cost of platinum currently the best-known catalyst for reducing oxygen in terms of both activity and stability. One solution is to decrease the amount of platinum required, for example by alloying, but without detrimentally affecting its properties. The alloy Pt_xY is known to be active and stable, but its synthesis in nanoparticulate form has proved challenging, which limits its further study. Herein we demonstrate the synthesis, characterization and catalyst testing of model Pt_xY nanoparticles prepared through the gas-aggregation technique. Themore » catalysts reported here are highly active, with a mass activity of up to 3.05 A mgPt^-1 at 0.9 V versus a reversible hydrogen electrode. Using a variety of characterization techniques, we show that the enhanced activity of Pt_xY over platinum results exclusively from a compressive strain exerted on the platinum surface atoms by the alloy core.« less