Interfacial effects on the catalysis of the hydrogen evolution, oxygen evolution and CO2-reduction reactions for (co-)electrolyzer development

Abstract

Our progressive transition from a society energetically dependent on fossil fuels towards one relying on renewable sources requires novel, environmentally friendly energy conversion and storage concepts. Hydrogen is widely regarded as an energy carrier that could circumvent this need, particularly in sight of the foreseeable spread of fuel cell cars that would use this "renewable H 2 ". The latter would be produced using electrolyzers, which in their better established form cannot fulfill the targeted H 2-price due to the low current densities (< 0.5 mA•cm geom-2) associated to their liquid electrolyte. Alternatively, devices based on proton-and anion-exchange membranes are currently under development, and a new kind of co-electrolysis cell in which CO 2 is reduced into hydrocarbons is also envisaged. Electrocatalysts play a crucial role in all of these systems, but the interplay between their surface and the reaction medium (in the so-called interface) is often overlooked in the quest towards better performance. With this motivation, this review discusses the current knowledge of the interfacial catalysis of the three (co-)electrolysis relevant reactions (i.e., the evolution of H 2 and O 2 , and the reduction of CO 2). From this, we identify pH and surface oxidation state as the key electrolyte-and surface-related parameters for which further understanding could lead to improved kinetics, and propose strategies for the tentative design of better electrocatalysts.

On the Oxidation State of Cu2O upon Electrochemical CO2 Reduction: An XPS Study

“…As such, our conclusions agree with those of recent computational [13] and experimental [15,16,31] studies by the Ager and Bell groups, and indirectly suggest that the product selectivity of oxide-derived Cu-catalysts is linked to their great roughness and corresponding abundance of ethylene-selective surface domains. Ultimately, our work additionally highlights the importance of careful sample transfer for drawing meaningful conclusions upon post-mortem surface characterization using ex situ techniques, [2] as well as the need for a continued development of operando characterization tools that can circumvent these limitations. [52] Table 1.…”

“…The electrochemical reduction of carbon dioxide to added‐value chemicals is gaining attention as a means to valorize CO 2 while decreasing its emissions and environmental impact . Despite this interest, the large overpotentials and poor selectivities displayed by most CO 2 ‐reduction electrocatalysts represent a major obstacle for the development of an implementable technology, which would additionally require a rigorous assessment of the CO 2 ‐reduction products with the greatest marketability potential . In this regard, some studies have suggested that CO 2 ‐electroreduction to formate or H 2 /CO mixtures (i. e., syngas) may be cost‐competitive when performed using Sn‐ or Au‐based catalysts implemented in electrode/cell configurations allowing to draw currents >100 mA⋅cm −2 .…”

“…[1] Despite this interest, the large overpotentials and poor selectivities displayed by most CO 2 -reduction electrocatalysts represent a major obstacle for the development of an implementable technology, which would additionally require a rigorous assessment of the CO 2 -reduction products with the greatest marketability potential. [2] In this regard, some studies have suggested that CO 2 -electroreduction to formate or H 2 /CO mixtures (i. e., syngas) may be cost-competitive when performed using Sn-or Au-based catalysts implemented in electrode/cell configurations allowing to draw currents > 100 mA·cm À 2 . [3][4][5] On the other hand, the production of ethylene or methanol using the same setups would lead to estimated production costs � 2-fold above current market values [3,4] -a price gap that could be significantly narrowed by substituting the copper catalysts considered in the above studies [3,4] with copper oxides, [6] which display enhanced selectivities and stabilities for CO 2 -toethylene/-methanol reduction.…”

Chemical Recognition of Active Oxygen Species on the Surface of Oxygen Evolution Reaction Electrocatalysts

“…Water splitting has been envisioned for decades as apromising strategy to produce clean and renewable hydrogen for energy storage.However,this process is largely hampered by the slow kinetics associated with the oxygen evolution reaction (OER), 2H 2 O!O 2 + 4H + + 4e À .T herefore,numerous studies have been conducted to understand and control this reaction. [1][2][3] While progress was made on the design of electrocatalysts for the OER, these studies point to the correlation between the activity and the stability for OER catalysts.T he surface of the most active oxides reconstructs during OER, resulting in amorphous oxyhydroxide structure, which consists of clusters of edge-shared octahedra. [4,5] One factor distinguishing molecular catalysts from solid catalysts is that, aside from their homogeneous nature,t he electrochemically formed high-valence metal-oxo species can form an O À Obond by either an acid-base reaction with water or via the direct coupling of two neighboring oxo species.…”

Unsupported Pt3Ni Aerogels as Corrosion Resistant PEFC Anode Catalysts under Gross Fuel Starvation Conditions

“…≈65 m 2 /g Pt for Pt/CB, ≈ 42 m 2 /g Pt for Pt/GCB and ≈30 m 2 /g Pt for Pt 3 Ni) can be excluded as a cause for this activity enhancement, since Pt/CB and Pt/GCB show similar i 0 's despite their different ECSAs, therefore confirming the absence of a particle size effect for the HER/HOR kinetics on Pt already discussed in several previous studies. 37,42,43 Coming back to the results of the AST with anode loadings of ≈50 μg Pt /cm …”