In recent decades, significant progress has been achieved in rational developments of electrocatalysts through constructing novel atomistic structures and modulating catalytic surface topography, realizing substantial enhancement in electrocatalytic activities. Numerous advanced catalysts were developed for electrochemical energy conversion, exhibiting low overpotential, high intrinsic activity, and selectivity. Yet, maintaining the high catalytic performance under working conditions with high polarization and vigorous microkinetics that induce intensive degradation of surface nanostructures presents a significant challenge for commercial applications. Recently, advanced operando and computational techniques have provided comprehensive mechanistic insights into the degradation of surficial functional structures. Additionally, various innovative strategies have been devised and proven effective in sustaining electrocatalytic activity under harsh operating conditions. This review aims to discuss the most recent understanding of the degradation microkinetics of catalysts across an entire range of anodic to cathodic polarizations, encompassing processes such as oxygen evolution and reduction, hydrogen reduction, and carbon dioxide reduction. Subsequently, innovative strategies adopted to stabilize the materials' structure and activity are highlighted with an in-depth discussion of the underlying rationale. Finally, we present conclusions and perspectives regarding future research and development. By identifying the research gaps, this review aims to inspire further exploration of surface degradation mechanisms and rational design of durable electrocatalysts, ultimately contributing to the large-scale utilization of electroconversion technologies.

Surface engineering for stable electrocatalysis.

Colorimetric sensors with instant visual readout are significant and highly required for convenient detection of various analytes, especially in the post-COVID-19 era. Noble metal-based bimetallic nanoparticles (NMBNPs), considered as promising nanoprobes for colorimetric sensing, are significantly superior to monometallic nanoparticles due to their improved optical property, catalytic activity, stability and selectivity. In this review, we focus on the recent progress in the colorimetric sensors based on NMBNPs with alloy, core-shell, core-satellite and Janus nanostructures. Firstly, we comprehensively introduce the synthesis approaches of NMBNPs which can be classified into three classes, including the top-down physical methods, bottom-up chemical methods and other emerging methods. Depending on these NMBNPs, the main sensing strategies exploiting their unique localized surface plasmon resonance (LSPR) property and nanozyme activity for various applications in colorimetric detection are critically summarized and discussed in detail. Finally, challenges and opportunities for the future development of NMBNPs-based colorimetric sensors are proposed and summarized. We hope that this review will help readers to better understand the current research status of NMBNPs for colorimetric sensing. 

Recent development of noble metal-based bimetallic nanoparticles for colorimetric sensing

The electrochemical oxidation of urea presents a promising avenue for hydrogen production with reduced energy consumption. Therefore, developing an efficient bifunctional electrocatalyst capable of catalyzing both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is of prominent importance. Herein, a cooperative P and Cr co-doped NiMoO4 hydrate electrode (P/Cr60-NiMoO4) is developed as a self-supported bifunctional electrode for energy-efficient urea-assisted H2 production. Benefiting from the cooperativity of both dopants, the P/Cr60-NiMoO4 electrocatalyst exhibits remarkable performance in UOR and HER, achieving 1.33 V and 35.7 mV at 10 mA cm−2, respectively. Moreover, the utilization of P/Cr60-NiMoO4 as a dual-functional catalyst only needs 1.35 V to reach 10 mA cm−2 in 1 M KOH electrolyte with 0.33 M urea, representing a reduction of 180 mV compared to conventional water electrocatalysis devices (OER//HER systems). Theoretical calculations based on density functional theory reveal that the superior activity of the P/Cr-incorporation system can be attributed to its ability to enhance interface electron concentration, promote electron transfer, and reduce the free energy barriers associated with both UOR and HER. 

Cooperative phosphorus and chromium doping induced electronic and morphological dual modulation in NiMoO4 hydrate for energy-efficient urea-assisted hydrogen production

Electrochemistry-driven techniques for advanced energy storage/conversion and environmental protection play a crucial role in achieving sustainable development goals. As an indispensable component in diverse electrochemical systems, electroactive materials gain soaring interest in terms of rational design and sustainable synthesis. Notably, mechanochemistry-based green and powerful synthesis has been widely employed to fabricate diverse electroactive materials, given their scalability and tunability. Recently, mechanochemically synthesized electroactive materials have been widely applied in various environmental and energy fields, leading to significant progress. However, a systematic analysis of these advancements is still missing. Herein, we comprehensively discuss recent achievements in mechanosynthesized electroactive materials for sustainable energy and environmental applications. The development of mechanochemical synthesis is introduced, along with different types of mechanosynthesized electroactive materials. Subsequently, the review delves into the applications of these materials in advanced energy conversion/storage systems and environmental remediation. The rational design of electroactive materials and their structure-performance correlation are illustrated by discussing the effects of the mechanochemical process on the internal and external properties of materials and their electrochemical performance. Lastly, key perspectives in this field are discussed, including mechanochemical process monitoring, field-assisted mechanochemical synthesis, material performance optimization, practical applications, and mechanochemistry-driven fuels/chemicals synthesis. By illustrating current advances and perspectives related to the development of mechanosynthesized electroactive materials, this review aims to shed some light on upcoming research on green mechanochemical synthesis-driven energy and environmental sustainability. 

Mechanosynthesized electroactive materials for sustainable energy and environmental applications: A critical review

As an oxygen reduction reaction (ORR) catalyst, nitrogen-doped carbon (NC) is widely used in zinc-air batteries (ZABs). However, NC catalysts exhibit low conductivity and insufficient exposure of active sites. Therefore, a Co-based deep eutectic solvent (DES) was selected to modify NC catalyst (Co-NC) to improve ORR performances. Density functional theory (DFT) calculation shows that the modification of Co-based DES can change the electronic structure of NC and increase metallic active sites, which is beneficial to the desorption of reaction intermediates on Co-NC, further improving ORR performance. Co-NC shows excellent ORR performances and stability. Impressively, ZABs assembled with Co-NC manifest a high maximum power density of 177.4 mW cm−2, a high specific capacity of 726.12 mA h g−1 and a charge-discharge cycle life of 500 h. This study can provide practical reference for surface modified carbon-based electrocatalyst with DES to improve ORR performances. 

Cobalt-Based Deep Eutectic Solvent Modified Nitrogen-Doped Carbon Catalyst for Boosting Oxygen Reduction Reaction in Zinc–Air Batteries

Non-precious metal catalysts show great promise to replace the state-of-the-art Pt-based catalysts for catalyzing the oxygen reduction reaction (ORR), while their catalytic activity still needs to be greatly improved before their broad-based application. Here, we report a facile approach to improving the performance of zeolitic imidazolate framework-derived carbon (ZDC) toward the ORR by incorporating a small amount of ionic liquid (IL). The IL would preferentially fill the micropores of ZDC and greatly enhance the utilization of the active sites within the micropores, which are initially not accessible due to insufficient surface wetting. It is also disclosed that the ORR activity in terms of kinetic current at 0.85 V depends on the loading amount of the IL, and the maximum activity is obtained at a mass ratio of IL to ZDC at 1.2. The optimum stems from the counterbalance between the enhanced utilization of the active sites within the micropores and the retarded diffusion of the reactants within the IL phase due to its high viscosity.

Increasing Accessible Active Site Density of Non-Precious Metal Oxygen Reduction Reaction Catalysts through Ionic Liquid Modification

Proton-exchange membrane fuel cells (PEMFCs) represent an essential technology for the future decarbonization of the transportation sector. A major component of PEMFCs is the catalyst, often Pt-based alloys supported on carbon black, which are sufficiently active and stable upon long-term operation under the harsh reaction conditions implied by PEMFCs. However, the catalyst synthesis is typically laborious and challenging to upscale, employing organic solvents, surfactants, or uneconomical metal deposition routes. To solve this, we offer a mechanochemically assisted two-step solvent-less methodology to produce supported metal catalysts, particularly supported PtNi and PtCo catalysts. Accordingly, metal salts are first dispersed on the designated support by planetary ball milling. Subsequently, the mixture is reduced with hydrogen and annealed under an inert atmosphere to yield supported alloyed nanoparticles. Notably, by applying our procedure to the synthesis of carbon-supported PtNi and PtCo nanoparticles, we demonstrate that size, composition, and total metal loading can be finely adjusted, leading to highly performant catalysts in the oxygen reduction reaction (ORR). 

Facile Solid-State Synthesis of Supported PtNi and PtCo Bimetallic Nanoparticles for the Oxygen Reduction Reaction

Controlled doping of carbon catalyst supports by atomic replacement via gasification-assisted heteroatom doping

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO
 2
 Reduction

Supported bimetallic catalysts composed of platinum and transition metals are highly investigated electrocatalysts for the oxygen reduction reaction (ORR) because of their enhanced activity and stability. However, common routes to synthesize these materials are often laborious and not scalable, employing organic solvents or uneconomical metal deposition methods [1-2]. Here, we present a mechanochemistry-assisted, dry and scalable synthesis route towards supported bimetallic catalysts, which consists of only two steps: First, metal salts are dispersed on a carbon support in a planetary mill without further additives. Following, the powder is reduced with hydrogen and annealed to yield alloyed catalysts. With this process, we are able to synthesize PtM/C catalysts where M was Ni, Co or Ru. Both metal loading and ratio could be adjusted by changing the amount of metal salt. The average size of the PtM-NPs was similarly controlled by changing the annealing temperature.
 With X-ray diffraction (XRD), we show that no metal or salt reflexes are present after milling and that the XRD pattern matches the carbon support. After reduction and annealing, clear reflexes of the targeted alloy composition are visible. The latter was confirmed by scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDX). After milling, ionic metal species are present as sub-nanometer clusters evenly dispersed over the carbon support. After reduction and annealing, PtM nanoparticles have formed. Neither by XRD nor by STEM-EDX was the presence of unalloyed Pt or M detected. Optical emission spectrometry was used to confirm the targeted loading and bulk composition of the catalysts.
 Due to the known high activity for catalyzing the ORR, PtNi/C and PtCo/C were subjected to electrochemical evaluation in a rotating disc electrode setup [2]. In both cases, specific activities surpassing 1 mA/cm2
 Pt at 0.9 V were reached. The electrochemically active surface area (ECSA) and mass activity were also in the range expected for the composition and particle size. To assess the stability, the catalysts were cycled from 0.4 to 1.0 V (RHE) with a scan rate of 1 V/s for 10800 cycles. The loss in ECSA of approximately 5 % was also in line with expectations. Since iron impurities are known to reduce the lifetime of a proton exchange membrane fuel cell, the milling process was adapted to a Si3N4-mill instead of a steel mill, again demonstrating the flexibility of this synthesis route [3].
 To conclude, the reported solid-state procedure allows the dry synthesis of supported bimetallic catalysts over a wide range of compositions. The materials show high activity and stability catalyzing the ORR. Due to its simplicity and flexibility, we expect this synthesis approach to be applied in other fields of catalysis within a short period of time.
 References:
 [1] K. Loza, M. Heggen, M. Epple, Adv. Funct. Mater., 2020, 30, 1909250.
 [2] I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy Environ. Sci., 2012, 5, 6744.
 [3] A. Collier, H. Wang, X. Z. Yuan, J. Zhang, D. P. Wilkinson, Int. J. Hydrog. Energy, 2006, 31, 1838–1854.
 [4] J. De Bellis, M. Felderhoff, F. Schüth, Chem. Mater., 2021, 33, 6, 2037–2045.
 
 
 
 
 
 Figure 1


Facile Solid-State Synthesis of Supported Ptm-Nps for the Oxygen Reduction Reaction

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Increasing Accessible Active Site Density of Non-Precious Metal Oxygen Reduction Reaction Catalysts through Ionic Liquid Modification

Facile Solid-State Synthesis of Supported PtNi and PtCo Bimetallic Nanoparticles for the Oxygen Reduction Reaction

Controlled doping of carbon catalyst supports by atomic replacement via gasification-assisted heteroatom doping

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO 2 Reduction

Facile Solid-State Synthesis of Supported Ptm-Nps for the Oxygen Reduction Reaction