Structurally ordered intermetallic compounds possess unique chemical and physical properties, making them an interesting class of materials for application in electrocatalytic reactions. This Review comprises the work on intermetallic compounds used for energy relevant electrocatalysis and is structured by the reactions in scope, which are the hydrogen evolution reaction (HER), electrochemical carbondioxide reduction reaction (eCO2RR), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR) as well as the oxidation reactions of formic acid (FAOR), methanol (MOR), and ethanol (EtOR). Optimization pathways for electrocatalysts, based on the adjustability of the intermetallic materials, are highlighted, and experimental data are provided in a comparative manner, to provide an overview, foundation, and reference for further development.

Efficient development of catalytic materials requires knowledge of the decisive parameters defining the catalytic properties. In multicomponent metallic catalysts, these are categorized as electronic and geometric effects, yet they are strongly interrelated. A systematic disentanglement can be achieved by fixing one parameter while altering the other, which becomes possible through the substitution in isostructural intermetallic compounds. This approach enables the evaluation of electronic or geometric contributions both individually and combined. Herein, this is achieved by substitution of indium (three valence electrons) with tin (four valence electrons) in the series In1–x Sn x Pd2, which allows for a systematic variation of the total number of electrons per unit cell with only a minor variation of the unit cell parameters and thus the evaluation of the electronic effect. Geometric effects were evaluated by substitution of indium with gallium in the Ga1–x In x Pd2 series, which allows for a systematic variation of the interatomic distances while maintaining the same number of valence electrons per unit cell and close atomic coordinates. By substituting gallium with tin in the Ga1–x Sn x Pd2 series, both effects are combined and addressed simultaneously. The activity enhancement of the methanol oxidation reaction on the Ga1–x Sn x Pd2 series is attributed to the synergy of the combined effects.

Molybdenum–nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo, and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel whether crystallographic ordering affects the activity. Their intrinsic instability leads to molybdenum leaching, resulting in higher specific surface areas and nickel-enriched surfaces. These are more prone to form Ni­(OH)2 layers, which leads to deactivation of the Mo–Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. Ni7Mo7, identified earlier as durable, proves to be highly unstable in the applied ADTs. The results show that the enhanced activity of unsupported bulk Mo–Ni electrodes can solely be ascribed to increased specific surface areas.

Besides activity and selectivity, the stability is of great importance in the development of catalysts for long-term applications. However, the lack of standardized stability protocols in electrocatalysis remains a fundamental hurdle hindering progress in the field by the lack of quantitative comparability of data in different studies. Herein, an electrochemical protocol to address the stability of bulk electrodes is developed. The protocol tests in situ and operando stability in the electrochemical methanol oxidation in alkaline media using the intermetallic compounds SnPd 2 and ZnPd 2 as test materials. Stability tests resulted in an equimolar mixture of 0.5 M methanol and 0.5 M KOH being the optimum composition of the electrolyte to obtain low corrosion rates and in ZnPd 2 being less stable than SnPd 2 . The reported protocol is a first, easy-to-do step to investigate the stability of electrode materials which is a prerequisite for application as well as a knowledge-based development of new electrode materials.

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Thin coatings of Bi2O3 were deposited on glass substrates by ultrasonic spray coating of THF solutions of the molecular precursor [Bi38O45(OMc)24(DMSO)9] ⋅ 2DMSO ⋅ 7H2O (OMc=O2CC3H5) followed by hydrolysis and subsequent annealing. Depending on the synthetic protocol, the bismuth oxido cluster was transformed into either α‐ or β‐Bi2O3. The as‐synthesized Bi2O3 coatings were characterized by powder X‐ray diffraction (PXRD), thickness measurements, diffuse reflectance UV‐Vis spectroscopy (DRS), photoluminescence (PL) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The thin coatings (thickness: 5–16 μm) were compared with regard to their performance in photocatalytic rhodamine B (RhB) decomposition under visible light irradiation. The β‐Bi2O3 coatings, that showed the highest photocatalytic activity, were used for the photocatalytic decomposition of other pollutants such as triclosan and ethinyl estradiol. In addition, the interplay between the photooxidation that is induced by the excitation of the catalyst using visible light and the photosensitized decomposition pathway was studied by degradation experiments of aqueous rhodamine B solutions using β‐Bi2O3 coatings.

Molybdenum-nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). This contribution investigates the potential influence of ordered crystal structures on the catalytic activity. Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel, whether crystallographic ordering affects the activity. Due to their intrinsic instability, molybdenum is leached resulting in higher specific surface areas and nickel-rich surfaces. The gain in surface area scales with the applied potential and the molybdenum content of the pristine samples. The nickel-enriched surfaces are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo-Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. The earlier as durable identified Ni7Mo7 proves to be highly unstable in the applied ADTs. The results indicate that the enhanced activity of unsupported bulk Mo-Ni electrodes can solely be ascribed to increased specific surface areas.

The isostructural region (Sn,Pb,Bi)Pt has been established over a wide range of the quasi-ternary section of the quaternary phase diagram. A synthesis protocol was developed, and single-phase compounds were thoroughly characterized, revealing linear relationships between the volume of the unit cell and the substitution degree for the NiAs type of crystal structure. Together with the already established (Pb,Bi)Pt series, the isostructural cut at 50 atom % Pt forms an ideal platform to independently investigate the influence of electronic and structural properties for physical and chemical applications, such as electrocatalysis. The three binary endmembers SnPt, PbPt, and BiPt are active materials in a variety of electrocatalytic oxidation and reduction reactions such as methanol oxidation and oxygen reduction, respectively. By gradual substitution, a fully independent tuning of interatomic distances and electronic densities can be achieved without altering the crystal structure. This unique adaptability is gated behind the requirement of extended homogeneity ranges of at least quaternary intermetallic compounds. Here, we present this new platform for systematic investigations in (electro) catalysis.