Understanding the activity transport nexus in water and CO2_{2} electrolysis: State of the art, challenges and perspectives

This article reviews the challenge of expanding the current research focus on water and CO2 electrolysis from catalyst-related insights towards achieving complete understanding of the activity transport nexus within full electrolysis cells. The challenge arises from the complex interaction of a multitude of phenomena taking place at different scales that span several orders of magnitude. An overview of current research on materials and components, experiments and simulations are provided. As well as obvious differences, there are similar principles and phenomena within water and CO$_{2}$ electrolysis technologies, which are extracted. Against this background, a perspective on required future research within the individual fields, and the need for a multidisciplinary research approach across natural, materials and engineering sciences to tackle the activity transport nexus is presented

Avoiding Pitfalls in Comparison of Activity and Selectivity of Solid Catalysts for Electrochemical HMF Oxidation

Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) offers a renewable approach to produce the value-added platform chemical 2,5-furandicarboxylic acid (FDCA). The key for the economic viability of this approach is to develop active and selective electrocatalysts. Nevertheless, a reliable catalyst evaluation protocol is still missing, leading to elusive conclusions on criteria for a high-performing catalyst. Herein, we demonstrate that besides the catalyst identity, secondary parameters such as materials of conductive substrates for the working electrode, concentration of the supporting electrolyte, and electrolyzer configurations have profound impact on the catalyst performance and thus need to be optimized before assessing the true activity of a catalyst. Moreover, we highlight the importance of those secondary parameters in suppressing side reactions, which has long been overlooked. The protocol is validated by evaluating the performance of free-standing Cu-foam, and CuCoO modified with NaPO2H2 and Ni, which were immobilized on boron-doped diamond (BDD) electrodes. Recommended practices and figure of merits in carefully evaluating the catalyst performance are proposed. © 2021 The Authors. Published by The Chemical Society of Japan & Wiley-VCH Gmb

Tandem Nanostructures: A Prospective Platform for Photoelectrochemical Water Splitting

A platform for efficient photoelectrochemical (PEC) water splitting must fulfil different requirements: the absorption of the solar spectrum should be maximized in use for charge carrier generation. To avoid recombination, fast separation of charge carriers is required and the energetic positions of the band structure(s) must be optimized with respect to the water splitting reactions. In these respects, constructing tandem nanostructures with rationally designed nanostructured units offers a potential opportunity to break the performance bottleneck imposed by the unitary nanostructure. So far, quite a few tandem nanostructures have been designed, fabricated, and employed to improve the efficiency of PEC water splitting, and significant achievements have been realized. This review focuses on the current advances in tandem nanostructures for PEC water splitting. Firstly, the state of the art for tandem nanostructures applied in PEC water splitting is summarized. Secondly, the advances in this field and advantages arising of employing tandem nanostructures for PEC water splitting are outlined. Subsequently, different types of tandem nanostructures are reviewed, including core‐shell tandem nanostructured photoelectrode, the two‐photoelectrode tandem cell, and the tandem nanostructures of plasmon related devices for PEC water splitting. Based on this, the future perspective of this field is proposed

Avoiding Pitfalls in Comparison of Activity and Selectivity of Solid Catalysts for Electrochemical HMF Oxidation

Electrocatalytic oxidation of 5‐hydroxymethylfurfural (HMF) offers a renewable approach to produce the value‐added platform chemical 2,5‐furandicarboxylic acid (FDCA). The key for the economic viability of this approach is to develop active and selective electrocatalysts. Nevertheless, a reliable catalyst evaluation protocol is still missing, leading to elusive conclusions on criteria for a high‐performing catalyst. Herein, we demonstrate that besides the catalyst identity, secondary parameters such as materials of conductive substrates for the working electrode, concentration of the supporting electrolyte, and electrolyzer configurations have profound impact on the catalyst performance and thus need to be optimized before assessing the true activity of a catalyst. Moreover, we highlight the importance of those secondary parameters in suppressing side reactions, which has long been overlooked. The protocol is validated by evaluating the performance of free‐standing Cu‐foam, and CuCoO modified with NaPO₂H₂ and Ni, which were immobilized on boron‐doped diamond (BDD) electrodes. Recommended practices and figure of merits in carefully evaluating the catalyst performance are proposed

Industrially Relevant Conditions in Lab‐Scale Analysis for Alkaline Water Electrolysis

Alkaline water electrolysis remains one of the most promising technologies for the large‐scale production of green hydrogen. However, further increases in efficiency remain elusive, as new electrode materials that are highly efficient in the laboratory cannot maintain their performance under industrial conditions. Within this work, we present a beaker cell setup, in which the industrial relevance of research materials can already be investigated in the laboratory by applying industrial conditions. Thus, the setup allows for testing at 80 °C in 30 wt. % KOH for more than 300 hours. Electrodes are contacted with an in‐house designed Ni tuck‐in holder and two types of reference electrodes are recommended. In addition, a protocol to unify catalyst research is introduced

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

The copper-catalyzed electrochemical CO2 reduction reaction represents an elegant pathway to reduce CO2 emissions while producing a wide range of valuable hydrocarbons. The selectivity for these products depends strongly on the structure and morphology of the copper catalyst. However, continued deactivation during catalysis alters the obtained product spectrum. In this work, we report on the stabilizing effect of three different carbon supports with unique pore structures. The influence of pore structure on stability and selectivity was examined by high-angle annular dark field scanning transmission electron microscopy and gas chromatography measurements in a micro-flow cell. Supporting particles into confined space was found to increase the barrier for particle agglomeration during 20 h of chronopotentiometry measurements at 100 mA cm−2 resembling long-term CO2 reduction conditions. We propose a catalyst design preventing coalescence and agglomeration in harsh electrochemical reaction conditions, exemplarily demonstrated for the electrocatalytic CO2 reduction. With this work, we provide important insights into the design of stable CO2 electrocatalysts that can potentially be applied to a wide range of applications

Strong Activity Changes Observable during the First Pretreatment Cycles of Trimetallic PtNiMo/C Catalysts

Pt‐based alloy catalysts supported on carbon are commonly characterized for oxygen reduction reaction (ORR) activity using the rotating disk electrode technique (RDE). Within this study, we show exemplarily for PtNiMo/C catalysts that the applied pretreatment influences strongly the determined activity. The classically employed descriptor of unchanged cyclic voltammetry response is insufficient to portrait completed surface restructuring, and gives an incorrect impression that stable activity can be determined. This might be one of the reasons for the strongly deviating activities reported in literature. Following the changes in activity during pretreatment also with in‐situ FTIR and online dissolution measurements gives insights to an up to now largely overseen high activity of the trimetallic catalysts. A maximum activity of 0.57 mA cmPt−2 at 0.95 VRHE is reached quickly during the first six cycles and decreases slowly subsequently. The maximum activity and change of activity over the cycle number is affected by the scan rate and electrolyte refreshing, while the gas atmosphere plays only a minor role. This exemplary study might be important for Pt alloy catalysts in general.An up to now unknown activity development is achieved during the pretreatment of alloyed trimetallic PtNiMo/C catalysts. In addition to the recording of steady state CVs under electrochemical cleaning cycles, insight into the unconditioned specific activity of the catalyst reveals a sharp increase during the first five to eight cycles and a further decrease at higher cycle numbers. image European Research Council (ERC)Deutsche Forschungsgemeinschaft (DFG)Federal Ministry of Education and Research (BMBF)Federal Ministry of Education and Research (BMBF)China Scholarship Council (CSC)National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809Shanghai Cooperation Organization Science and Technology Partnership Projec

Aqueous-phase reforming of xylitol over Pt/C and Pt/TiC-CDC catalysts: catalyst characterization and catalytic performance

The aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM. The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF