Silica-Derived Nanostructured Electrode Materials for ORR,OER, HER,CO2RR Electrocatalysis,and Energy Storage Applications: A Review**

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords “silica”, “electrocatalysts”, “ORR”, “OER”, “HER”, “HOR”, “CO₂RR”, “batteries”, and “supercapacitors”. The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.     

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂, IrP₂, PtP₂, RuB₂, Ru₂B₃, RuS₂, etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂, IrP₂, PtP₂, RuB₂, Ru₂B₃, RuS₂, etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.     

Mass‐Production of Mesoporous MnCo2O4 Spinels with Manganese(IV)‐ and Cobalt(II)‐Rich Surfaces for Superior Bifunctional Oxygen Electrocatalysis

A mesoporous MnCo₂O₄ electrode material is made for bifunctional oxygen electrocatalysis. The MnCo₂O₄ exhibits both Co₃O₄‐like activity for oxygen evolution reaction (OER) and Mn₂O₃‐like performance for oxygen reduction reaction (ORR). The potential difference between the ORR and OER of MnCo₂O₄ is as low as 0.83 V. By XANES and XPS investigation, the notable activity results from the preferred Mn^IV‐ and Co^II‐rich surface. The electrode material can be obtained on large‐scale with the precise chemical control of the components at relatively low temperature. The surface state engineering may open a new avenue to optimize the electrocatalysis performance of electrode materials. The prominent bifunctional activity shows that MnCo₂O₄ could be used in metal–air batteries and/or other energy devices.     

Molecular Engineering of a 3D Self‐Supported Electrode for Oxygen Electrocatalysis in Neutral Media

Electrodes for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are required in energy conversion and storage technologies. An assembly strategy involves covalently grafting Co corrole 1 onto Fe₃O₄ nanoarrays grown on Ti mesh. The resulted electrode shows significantly improved activity and durability for OER and ORR in neutral media as compared to Fe₃O₄ alone and with directly adsorbed 1 . It also displays higher atom efficiency (at least two magnitudes larger turnover frequency) than reported electrodes. Using this electrode in a neutral Zn‐air battery, a small charge–discharge voltage gap of 1.19 V, large peak power density of 90.4 mW cm^?2, and high rechargeable stability for >100 h are achieved, opening a promising avenue of molecular electrocatalysis in a metal–air battery. This work shows a molecule‐engineered electrode for electrocatalysis and demonstrates their potential applications in energy conversion and storage.     

Recent advances in one-dimensional nanostructures for energy electrocatalysis

Catalysts play decisive roles in determining the energy conversion efficiencies of energy devices. Up to now, various types of nanostructured materials have been studied as advanced electrocatalysts. This review highlights the application of one-dimensional (1D) metal electrocatalysts in energy conversion, focusing on two important reaction systems—direct methanol fuel cells and water splitting. In this review, we first give a broad introduction of electrochemical energy conversion. In the second section, we summarize the recent significant advances in the area of 1D metal nanostructured electrocatalysts for the electrochemical reactions involved in fuel cells and water splitting systems, including the oxygen reduction reaction, methanol oxidation reaction, hydrogen evolution reaction, and oxygen evolution reaction. Finally, based on the current studies on 1D nanostructures for energy electrocatalysis, we present a brief outlook on the research trend in 1D nanoelectrocatalysts for the two clean electrochemical energy conversion systems mentioned above.     

Advances in efficient electrocatalysts based on layered double hydroxides and their derivatives

The explore and development of electrocatalysts have gained significant attention due to their indispensable status in energy storage and conversion systems, such as fuel cells, metal–air batteries and solar water splitting cells. Layered double hydroxides(LDHs) and their derivatives(e.g., transition metal alloys, oxides, sulfides, nitrides and phosphides) have been adopted as catalysts for various electrochemical reactions, such as oxygen reduction, oxygen evolution, hydrogen evolution, and CO_2 reduction, which show excellent activity and remarkable durability in electrocatalytic process. In this review, the synthesis strategies, structural characters and electrochemical performances for the LDHs and their derivatives are described. In addition, we also discussed the effect of electronic and geometry structures to their electrocatalytic activity. The further development of high-performance electrocatalysts based on LDHs and their derivatives is covered by both a short summary and future outlook from the viewpoint of the material design and practical application.     

Oxygen Reduction on Ag(100) in Alkaline Solutions—A Theoretical Study

Silver is much more reactive to oxygen than gold; nevertheless, in alkaline solutions, the rates of oxygen reduction on both metals are similar. To explain this phenomenon, the first, rate‐determining step of oxygen reduction on Ag(100) is determined by a combination of DFT, molecular dynamics, and electrocatalysis theory. In vacuum, oxygen is adsorbed on Ag(100), but in the electrochemical environment, the adsorption energy is offset by the loss of hydration energy as the molecule approaches the surface. As a result, the first electron transfer should take place in an outer‐sphere mode. Previously, the same mechanism for oxygen reduction on Au(100) has been predicted, and these calculations have been repeated by using a more advanced version of the electrocatalysis theory discussed herein to confirm previous conclusions. The theoretical results compare well with experimental data.     

Emergence of CO2 electrolyzers including supported molecular catalysts

With access to cheap, sustainable electricity, electrocatalysis is a promising technology for converting electric power into storable chemical fuels or value-added chemical compounds. This has sparked the development of electrocatalysts that need to operate at high product selectivity and high energy efficiency. Electrocatalytic alcohol oxidation, oxygen activation and nitrogen and carbon dioxide (CO₂) reduction are examples of reactions with a huge industrial potential. Notably, electrocatalytic reduction of CO₂ has recently developed as a favourable pathway to convert this greenhouse gas into value-added chemicals and fuels. Earth-abundant metals stabilized by carbon/nitrogen macrocycle ligands are well-known efficient and selective catalysts for the electrochemical reduction of CO₂ in homogeneous conditions. Recently, such catalysts have also been used in supported conditions and implemented in flow cell electrolyzers, showing promising performances. This review provides a synopsis for the evolution of CO₂ electrolyzers using molecular catalysts.     

On the efficacy of electrocatalysis in nonaqueous Li-O2 batteries

Heterogeneous electrocatalysis has become a focal point in rechargeable Li-air battery research to reduce overpotentials in both the oxygen reduction (discharge) and especially oxygen evolution (charge) reactions. In this study, we show that past reports of traditional cathode electrocatalysis in nonaqueous Li-O(2) batteries were indeed true, but that gas evolution related to electrolyte solvent decomposition was the dominant process being catalyzed. In dimethoxyethane, where Li(2)O(2) formation is the dominant product of the electrochemistry, no catalytic activity (compared to pure carbon) is observed using the same (Au, Pt, MnO(2)) nanoparticles. Nevertheless, the onset potential of oxygen evolution is only slightly higher than the open circuit potential of the cell, indicating conventional oxygen evolution electrocatalysis may be unnecessary.     

Nanostructured MoS2 Nanorose/Graphene Nanoplatelet Hybrids for Electrocatalysis

Tailoring and enhancing electrocatalytic activity is of the utmost importance from the viewpoints of sustainable energy and sensing. MoS₂ and graphene show great promise for the electrocatalysis of many reactions. Given that both graphene and MoS₂ are highly anisotropic in nature, with edge planes that are several orders of magnitude more catalytically active than basal planes, a new hybrid material with maximized edge‐plane density to provide efficient electron transfer, high catalytic activity, and conductive cores was engineered. The hybrid material consists of radial MoS₂ nanosheets with a high density of edge planes and unsaturated active sulfur atoms as well as interspersed with conductive graphene nanoplatelets. This hybrid material exhibits excellent activity for the hydrogen evolution reaction and the detection of DNA nucleobases. Such a nanoengineered, nanostructured hybrid material may play a major role in future electrocatalytic devices.     

Nano-Impact Single-Entity Electrochemistry Enables Plasmon-Enhanced Electrocatalysis**

Plasmon-enhanced electrocatalysis (PEEC), based on a combination of localized surface plasmon resonance excitation and an electrochemical bias applied to a plasmonic material, can result in improved electrical-to-chemical energy conversion compared to conventional electrocatalysis. Here, we demonstrate the advantages of nano-impact single-entity electrochemistry (SEE) for investigating the intrinsic activity of plasmonic catalysts at the single-particle level using glucose electrooxidation and oxygen reduction on gold nanoparticles as model reactions. We show that in conventional ensemble measurements, plasmonic effects have minimal impact on photocurrents. We suggest that this is due to the continuous equilibration of the Fermi level (E_F) of the deposited gold nanoparticles with the E_F of the working electrode, leading to fast neutralization of hot carriers by the measuring circuit. The photocurrents detected in the ensemble measurements are primarily caused by photo-induced heating of the supporting electrode material. In SEE, the E_F of suspended gold nanoparticles is unaffected by the working electrode potential. As a result, plasmonic effects are the dominant source of photocurrents under SEE experimental conditions.     

A review of transition metal chalcogenide/graphene nanocomposites for energy storage and conversion

Recent advances in the applications of transition metal chalcogenides/graphene (TMC/graphene) nanocomposites in future energy storage and conversion are reviewed. The synthesis processes and structures of TMC/graphene, workingpriciple of evergy energy device, and the electrochemical performances are summarized.     

Electrocatalysis and pH (a review)

The factors determining pH effects on principal catalytic reactions in low-temperature fuel cells (oxygen reduction, hydrogen oxidation, and primary alcohols oxidation) are analyzed. The decreasing of hydrogen oxidation rate when passing from acidic electrolytes to basic ones was shown to be due to the electrode surface blocking by oxygen-containing species and changes in the adsorbed hydrogen energy state. In the case of oxygen reduction, the key factors determining the process’ kinetics and mechanism are: the O₂ adsorption energy, the adsorbed molecule protonation, and the oxygen reaction thermodynamics. The process’ high selectivity in acidic electrolytes at platinum electrodes is caused by rather high Pt-O₂ bond energy and its protonation. The passing from acidic electrolytes to basic ones involves a decrease in the oxygen adsorption energy, both at platinum and nonplatinum catalysts, hence, in the selectivity of the oxygen-to-water reduction reaction. The increase in the methanol and ethanol oxidation rate in basic media, as compared with acidic ones, is due to changes in the reacting species’ structure (because of the alcohol molecules dissociation) on the one hand, and active OH_ads species inflow to the reaction zone, on the other hand. In the case of ethanol, the above-listed factors determine the process’ increased selectivity with respect to CO₂ at higher pHs. Based on the survey and valuation, priority guidelines in the electrocatalysis of commercially important reactions are formulated, in particular, concepts of electrocatalysis at nonplatinum electrode materials that are stable in basic electrolytes, and approaches to the practical control of the rate and selectivity of oxygen reduction and primary alcohols oxidation over wide pH range.     

Copolymer-Induced Intermolecular Charge Transfer: Enhancing the Activity of Metal-Free Catalysts for Oxygen Reduction

Breaking the electroneutrality of sp² carbon lattice is a viable way for nanocarbon material to modulate the charge delocalization and to further alter the electrocatalytic activity. Positive charge spreadsheeting is preferable for catalyzing the oxygen reduction reaction (ORR) and other electrochemical reactions. Analogously to the case of intramolecular charge transfer by heteroatom doping, electrons in the conjugated carbon lattice can be redistributed by the intermolecular charge transfer from the nanocarbon material to the polyelectrolyte. A copolymeric electrolyte, epichlorohydrin-dimethylamine copolymer (EDC) was synthesized. The EDC-modified carbon nanotube (CNT) hybrid was subsequently fabricated by sonication treatment and served as a metal-free carbonaceous electrocatalyst with remarkable catalytic activity and stability. The resultant hybrid presents positive charge spreadsheeting on CNT as a result of the interfacial electron transfer from CNT to EDC. DFT calculations were further carried out to reveal that the enhancement of the wrapped EDC polyelectrolyte originates from the synergetic effect of the quaternary ammonium-hydroxyl covalently bonded structure. The CNT-EDC hybrid not only provides an atomically precise regulation to modulate nanocarbon materials from inactive carbonaceous materials into efficient metal-free catalysts, but it also opens new avenues to develop metal-free catalysts with well-defined and highly active sites.     

自支撑单原子膜电极在能源电催化中的应用

单原子催化剂的催化活性高, 稳定性强, 原子利用率高, 在能源电催化领域已被广泛研究. 然而, 粉末状(颗粒状)单原子催化材料存在工作电极制备过程复杂、 黏结剂添加降低导电性且占据催化材料的体积、 活性位点易被包埋等问题, 在作为电极材料催化能源转化过程时, 载量通常小于1 mg/cm², 反应电流密度不高于100 mA/cm². 与单原子催化剂相比, 自支撑单原子膜电极不仅具有单原子催化剂的诸多优势, 同时展现出整体式电极的特点, 例如无需添加黏结剂、 导电性好、 单原子活性位点暴露率高、 形貌与孔结构可调控等, 在大电流电催化反应、 高能量高功率密度电池等领域拥有应用前景. 本文综合评述了面向能源电催化应用的自支撑单原子膜电极的研究进展, 讨论了自支撑单原子膜电极的优势, 总结了自支撑单原子膜电极的合成方法, 包括自支撑基底上原位制备法、 静电纺丝法、 自组装法、 化学气相沉积与固相扩散法等, 介绍了其在析氢反应、 析氧反应、 电化学制过氧化氢反应、 锌空电池、 二氧化碳还原反应及锂硫电池中的应用, 并对该类电极的发展方向进行了展望.     

Polyoxometalate-Based Compounds for Photo- and Electrocatalytic Applications

Photo/electrocatalysis of water (H₂O) splitting and CO₂ reduction reactions is a promising strategy to alleviate the energy crisis and excessive CO₂ emissions. For the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO₂ reduction reaction (CO₂RR) involved, the development of effective photo/electrocatalysts is critical to reduce the activation energy and accelerate the sluggish dynamics. Polyoxometalate (POM)-based compounds with tunable compositions and diverse structures are emerging as unique photo/electrocatalysts for these reactions as they offer unparalleled advantages such as outstanding solution and redox stability, quasi-semiconductor behaviour, etc. This Minireview provides a basic introduction related to photo/electrocatalytic HER, OER and CO₂RR, followed by the classification of pristine POM-based compounds toward different catalytic reactions. Recent breakthroughs in engineering POM-based compounds as efficient photo/electrocatalysts are highlighted. Finally, the advantages, challenges, strategies and outlooks of POM-based compounds on improving photo/electrocatalytic performance are discussed.     

Decoupled Artificial Photosynthesis

Natural photosynthesis (NP) generates oxygen and carbohydrates from water and CO₂ utilizing solar energy to nourish lives and balance CO₂ levels. Following nature, artificial photosynthesis (AP), typically, overall water or CO₂ splitting, produces fuels and chemicals from renewable energy. However, hydrogen evolution or CO₂ reduction is inherently coupled with kinetically sluggish water oxidation, lowering efficiencies and raising safety concerns. Decoupled systems have thus emerged. In this review, we elaborate how decoupled artificial photosynthesis (DAP) evolves from NP and AP and unveil their distinct photoelectrochemical mechanisms in energy capture, transduction and conversion. Advances of AP and DAP are summarized in terms of photochemical (PC), photoelectrochemical (PEC), and photovoltaic-electrochemical (PV-EC) catalysis based on material and device design. The energy transduction process of DAP is emphasized. Challenges and perspectives on future researches are also presented.     

高熵纳米合金在电化学催化中的应用

The implementation of clean energy techniques, including clean hydrogen generation, use of solar-driven photovoltaic hybrid systems, photochemical heat generation as well as thermoelectric conversion, is crucial for the sustainable development of our society. Among these promising techniques, electrocatalysis has received significant attention for its ability to facilitate clean energy conversion because it promotes a higher rate of reaction and efficiency for the associated chemical transformations. Noble-metal-based electrocatalysts typically show high activity for electrochemical conversion processes. However, their scarcity and high cost limit their applications in electrocatalytic devices. To overcome this limitation, binary catalysts prepared by alloying with transition metals can be used. However, optimization of the activity of the binary catalysts is considerably limited because of the presence of the miscibility gap in the phase diagram of binary alloys. The activity of binary electrocatalysts can be attributed to the adsorption energy of molecules and intermediates on the surface. High-entropy alloys (HEAs), which consist of diverse elements in a single NP, typically exhibit better physical and/or chemical properties than their single-element counterparts, because of their tunable composition and inherent surface complexity. Further, HEAs can improve the performance of binary electrocatalysts because they exhibit a near-continuous distribution of adsorption energy. Recently, HEAs have gained considerable attention for their application in electrocatalytic reactions. This review summarizes recent research advances in HEA nanostructures and their application in the field of electrocatalysis. First, we introduce the concept, structure, and four core effects of HEAs. We believe that this part will provide the basic information about HEAs. Next, we discuss the reported top-down and bottom-up synthesis strategies, emphasizing on the carbothermal shock method, nanodroplet-mediated electrodeposition, fast moving bed pyrolysis, polyol process, and dealloying. Other methods such as combinatorial co-sputtering, ultrashort-pulsed laser ablation, ultrasonication-assisted wet chemistry, and scanning-probe block copolymer lithography are also highlighted. Among these methods, wet chemistry has been reported to be effective for the formation of nano-scale HEAs because it facilitates the concurrent reduction of all metal precursors to form solid-solution alloys. Next, we present the theoretical investigation of HEA nanocatalysts, including their thermodynamics, kinetic stability, and adsorption energy tuning for optimizing their catalytic activity and selectivity. To elucidate the structure–property relationship in HEAs, we summarize the research progress related to electrocatalytic reactions promoted by HEA nanocatalysts, including the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, methanol oxidation reaction, and CO₂ reduction reaction. Finally, we discuss the challenges and various strategies toward the development of HEAs.     

Challenges in the understanding oxygen reduction electrocatalysis on transition metal oxides

Transition metal oxides are attractive noble metal-free catalysts of the oxygen reduction for application at the cathode of alkaline membrane fuel cells or metal-air batteries. However, despite of a rapidly increasing number of publications devoted to the oxygen electrocatalysis on transition metal oxides, a clear picture regarding the relations between their structure and composition on the one hand and electrocatalytic activity on the other hand is lacking. This short review discusses challenges facing researchers seeking to understand electrocatalysis of the oxygen reduction reaction on transition metal oxides.