Because H2 is considered a promising clean energy source, water electrolysis has attracted great interest in related research and technology. Noble‐metal‐based catalysts are used as electrode ...materials in water electrolyzers, but their high cost and low abundance have impeded them from being used in practical areas. Recently, metal sulfides and phosphides based on earth‐abundant transition metals have emerged as promising candidates for efficient water‐splitting catalysts. Most studies have focused on adjusting the composition of the metal sulfides and phosphides to enhance the catalytic performance. However, morphology control of catalysts, including faceted and hollow structures, is much less explored for these systems because of difficulties in the synthesis, which requires a deep understanding of the nanocrystal growth process. Herein, representative synthetic methods for morphology‐controlled metal sulfides and phosphides are introduced to provide insights into these methodologies. The electrolytic performance of morphology‐controlled metal sulfide‐ and phosphide‐based nanocatalysts with enhanced surface area and intrinsically high catalytic activity is also summarized and the future research directions for this promising catalyst group is discussed.
Metal sulfide and phosphide nanoparticles have emerged as viable alternatives to expensive noble‐metal‐based electrocatalysts for water splitting. The recent significant developments of morphology‐controlled metal sulfide and phosphide nanoparticles as electrcatalysts for the hydrogen evolution reaction and oxygen evolution reaction are addressed.
The design and synthesis of Pt‐based electrocatalysts for the hydrogen evolution reaction (HER) are of great importance for the successful development of hydrogen‐based alternative energy ...technologies. Although Pt is considered to be the most active catalyst for the HER, its reaction performance is limited in alkaline solutions owing to a slow rate for water dissociation. Therefore, many research groups have intensively investigated reaction mechanisms and developed system designs and efficient Pt‐based catalysts to enhance the alkaline HER. Herein, we summarize the catalytic surface specificity of Pt and Pt–Ni(OH)2 materials to control the kinetics of the alkaline HER. In particular, we increase our understanding of Ni(OH)2‐modified Pt surfaces and the corresponding nanoscaled Pt–Ni(OH)2 electrocatalysts to improve the sluggish water‐dissociation step, and this knowledge will guide us to future sustainable energy applications of advanced nanomaterials.
Alkaline hydrogen: The alkaline hydrogen evolution reaction (HER) at Pt surfaces proceeds through Volmer–Heyrovsky and Volmer–Tafel mechanisms. If the Pt surface is modified with Ni(OH)2 clusters, the Volmer–Tafel mechanism with a promoted rate‐determining Volmer step and subsequent H2 generation will dominate. Benefitting from bifunctionality, the nanoscaled Pt–Ni(OH)2‐based electrocatalyst shows highly improved HER performance in alkaline electrolytes.
Long‐term catalyst stability is essential for the commercialization of hydrogen generation by electrocatalytic water‐splitting. Current research, however, mainly focuses on improving electrode ...activity of the hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode of electrolyzers, although the maintenance of long‐term performance poses a bigger challenge. To shift the focus of research to the issue of catalyst stability, this review describes the mechanism of HER/OER catalyst degradation based on catalyst dissolution and agglomeration, and summarizes representative catalyst designs for achieving stable catalysts in long‐term water electrolysis operation. Additionally, various strategies toward the improvement of HER/OER stability are evaluated, and potential effective guidelines for the design of stable catalysts are suggested.
Long term stability of nanocatalysts is critical to the commercialization of proton/anion exchange membrane water electrolysis. This review discusses various reasons for catalyst degradation such as element dissolution and catalyst agglomeration in conjunction with the relevant catalysis operation conditions. Then, catalyst design strategies are presented to help realize the long‐term operation of water electrolysis in practical environments.
A synthesis strategy for the preparation of ultrathin free‐standing ternary‐alloy nanosheets is reported. Ultrathin Pd‐Pt‐Ag nanosheets with a thickness of approximately 3 nm were successfully ...prepared by co‐reduction of the metal precursors in an appropriate molar ratio in the presence of CO. Both the presence of CO and the interplay between the constituent metals provide fine control over the anisotropic two‐dimensional growth of the ternary‐alloy nanostructure. The prepared Pd‐Pt‐Ag nanosheets were superior catalysts of ethanol electrooxidation owing to their specific structural and compositional characteristics. This approach will pave the way for the design of multicomponent 2D nanomaterials with unprecedented functions.
Ultrathin Pd‐Pt‐Ag nanosheets with a thickness of approximately 3 nm were successfully prepared by the co‐reduction of suitable metal precursors in an appropriate molar ratio in the presence of CO. These nanosheets are superior catalysts of ethanol electrooxidation owing to their specific structural and compositional characteristics.
Atomically ordered intermetallic nanoparticles exhibit improved catalytic activity and durability relative to random alloy counterparts. However, conventional methods with time‐consuming and ...high‐temperature syntheses only have rudimentary capability in controlling the structure of intermetallic nanoparticles, hindering advances of intermetallic nanocatalysts. We report a template‐directed strategy for rapid synthesis of Pd‐based (PdM, M=Pb, Sn and Cd) ultrathin porous intermetallic nanosheets (UPINs) with tunable sizes. This strategy uses preformed seeds, which act as the template to control the deposition of foreign atoms and the subsequent interatomic diffusion. Using the oxygen reduction reaction (ORR) as a model reaction, the as‐synthesized Pd3Pb UPINs exhibit superior activity, durability, and methanol tolerance. The favored geometrical structure and interatomic interaction between Pd and Pb in Pd3Pb UPINs are concluded to account for the enhanced ORR performance.
This template‐directed synthetic strategy is a universal route for shape‐controlled synthesis of intermetallic nanocrystals and will provide new opportunities for intermetallic nanocatalysts.
Because the hydrogen evolution reaction (HER) in alkaline electrolyzers is initiated by water dissociation, the hydrogen evolution kinetics are sluggish even on highly active Pt catalysts. Here, we ...have synthesized Ni(OH)2‐decorated Pt nanocubes as a bifunctional catalyst to enhance the HER kinetics in an alkaline medium. Electrochemical cyclic voltammetry and CO‐stripping measurements confirmed the selective deposition of Ni(OH)2 on the Pt(1 0 0) facets of nanocubes. Electrocatalytic HER activity of the Ni(OH)2‐decorated Pt nanocubes demonstrated that the bifunctional catalytic surface promotes the Volmer step kinetics and thus the Volmer/Tafel coupling dominant. As the result, catalytic surface specificity of Ni(OH)2‐decorated Pt nanocubes enhanced water dissociation, reduced contamination of OHad on Pt surface, and maintained long‐term HER performance in alkaline electrolytes.
Coated cubes: Pt nanocubes decorated with Ni(OH)2 as electrocatalysts are synthesized and their surface specificity are characterized. The Ni(OH)2‐decorated Pt nanocubes/C exhibit efficient electrocatalytic activity for the hydrogen evolution reaction in an alkaline electrolyte owing to the Volmer/Tafel dominant reaction pathway.
The harsh operating conditions of the oxygen evolution reaction (OER) in water electrolysis severely degrade the activity and stability of the electrocatalysts due to elemental leaching or particle ...agglomeration. Therefore, it is crucial to incorporate support materials that effectively immobilize catalyst particles for developing efficient OER catalysts. This review aims to highlight the role of MXene as a support material to improve the performance of OER catalysts. First, the extended OER mechanism is briefly described in terms of the effect of MXene support on OER catalysts. Then, various synthesis methods of MXene and catalyst‐MXene compounds are introduced, and important properties of MXene that are beneficial to improve OER performances are discussed. The electrocatalytic results of the enhanced OER catalysts due to the effective MXene support are also summarized. Finally, future challenges and prospects are proposed for utilizing MXene as an excellent support material for various electrocatalysis.
This article reviews the properties of MXene as a support material for enhancing oxygen evolution reaction (OER) performances. MXene enhances OER performance due to its ability to improve the conductivity, stability, and hydrophilicity of the catalyst. This review also highlights the advantages of MXene compared to other materials and provides future directions for utilizing MXene for various electrocatalysis.
This work proposes a multiscale modeling and model‐based feedback control framework for the delignification process in a batch‐type pulp digester. Specifically, we focus on a hardwood chip in the ...digester and develop a multiscale model capturing both the evolution of microscopic properties such as the pore size and shape distributions in the solid phase and the dynamic changes in the temperature and component concentrations in the liquor phase. While the macroscopic model adopts the continuum hypothesis based on the Purdue model, a novel microscopic model is developed using a kinetic Monte Carlo algorithm, accounting for the dissolution of lignin, cellulose, and hemicellulose contacting the liquor phase. A reduced‐order model was built to design a Luenberger observer for state estimation, which is then used to develop a model‐based control system. The simulation results demonstrated that the proposed methodology was able to regulate both the Kappa number and porosity to desired values.
This work presents the application of a Koopman operator approach to a batch pulp digester. To manufacture paper products with desired properties, it is essential to consider both macroscopic and ...microscopic attributes of pulp. However, the complexity of multiscale dynamics of pulping processes hinders proper control system design. Therefore, we utilize extended dynamic mode decomposition (EDMD), which is based on Koopman operator theory, to derive a global linear representation of a pulp digester. Then, we design an offset‐free Koopman‐based model predictive control (KMPC) system to regulate the Kappa number and cell wall thickness (CWT) of fibers at a batch pulp digester while compensating for the influence of plant‐model mismatch and disturbance during operation. The numerical experiments demonstrate that the linear state‐space model, obtained via EDMD, properly predicts the behavior of a batch pulp digester, and the designed offset‐free KMPC system successfully drives the Kappa number and CWT to set‐point values.
Dissolution of Ir oxides in Ir‐based catalysts, which is closely linked to the catalyst activity and stability toward the oxygen evolution reaction (OER) in acidic media, is a critical unresolved ...problem in the commercialization of water electrolysis. Doping foreign elements into the Ir oxides can accomplish an optimal combination of Ir oxidation states that is conducive to the leaching‐resistance of active catalytic sites. Here, it is reported that Pt doping into IrOx‐based nanoframe is beneficial in both terms of activity and stability. The Pt‐doped IrOx‐based nanoframe achieves the mass activity of 0.644 A mg−1Ir+Pt at 1.53 VRHE, which is 15‐fold higher than that of the commercial IrO2. During the accelerated durability test, the IrIV‐to‐IrIII ratio of 5 is maintained in the presence of Pt dopant to effectively mitigate the degradation of Ir catalyst, leading to the superb catalyst durability in acidic media.
The proper degree of Pt doping in electrochemically activated IrOx based catalysts is the key to forming defective and amorphous IrOx surfaces, and optimizing the active IrIII and stable IrIV, which is beneficial for high activity and stability toward the oxygen evolution reaction in acidic media.
