Degree Of Hydration Research Articles

Performance Evaluation of Stabilized Soils with Selected Common Waste Materials of Rice Husk Ash, Steel Slag and Iron Tailing Powder

Soil stabilization technology has been applied for a long time in the infrastructure construction field. Currently, the use of waste materials as stabilizer is growing in attention, because it promises to develop green and high-performance soil stabilization efficiency. In this work, three common waste materials, including rice husk ash (RHA), steel slag (SS) and iron tailing (IT) powder, were selected and synergistically utilized with cement to prepare stabilized soil. The mechanical strength, hydration degree and microstructure of the stabilized soil samples were tested. The experimental results showed that the mechanical strengths of the samples were improved as the cement content increased. To be specific, RHA-blended samples exhibited the lowest strengths compared with those incorporating SS and IT, indicating the poor effect of RHA on stimulating strength improvement. Moreover, SS and IT showed a much more significant effect on enhancing the mechanical strength for the stabilized soil samples, and the strength increasing rates can reach up to 60% compared to the reference batch. In addition, microstructural analysis results further verified the benefits of cement and waste materials on improving the performance of stabilized soil samples, as the hydration reaction and pore structure were proven to be improved with the aid of waste materials. This work gives insights into environmentally friendly road construction with high utilization of selected common wastes.

The Preparation of C-S-H Powder Seeds and Their Effect on the Early Hydration Performance of Cement Paste

C-S-H/PCE suspension can boost the hydration degree and strength of cement composite binding. However, the suspension will inevitably precipitate after a period of time, which is not conducive to its preservation, and its low solid content increases transportation costs in practical applications. In this study, utilizing synthetic PCE as a template, C-S-H/PCE suspension was synthesized using a co-precipitation method. Subsequently, powder seeds were produced via the spray-drying technique, and these prepared powder seeds were analyzed via microscopic characterization. The impact of these powder nucleating agents on cement hydration kinetics was evaluated through hydration heat measurements and hydration degree, fluidity, and compressive strength testing. The results indicated that these powder seeds exhibited a nano-film morphology. Their nucleation effect significantly enhanced the cement hydration rate, increased the degree of hydration, and improved strength. The hydration kinetics showed that the hydration of cement mixed with nucleating agents was not governed by a single reaction mechanism, but rather constitutes a complex, multi-component reaction process. As the content of nucleating agents increased, higher dosages of nucleating agents accelerated the production of more products within a short period, causing the system to rapidly transition to phase boundary reaction control. When the dosage of nucleating agents reached 2%, the cement hydration process bypassed the phase boundary reaction control stage and transitioned directly from the crystallization nucleation and crystal growth control process to the diffusion-controlled phase. Although the influence of powder seeds on the enhancement of the early-stage strength of mortar was slightly lower than that of the suspension, the powder was beneficial to its storage and transportation. Therefore, it has the potential to replace the suspension.

Uma investigação sobre o impacto da adição combinada de microfibra de celulose e microcelulose cristalina no desempenho dos compósitos de cimento Portland

Abstract The study of the effects of cellulosic materials as additives in matrices based on mineral binders is essential for the development of high-performance and more durable construction materials. In this context, the present research aims to propose composite systems incorporating cellulose microparticles and microfibers into cementitious matrices. The proposed systems were developed using CP V ARI cement, with cellulose microfiber (FC) contents of 0.5%, 1%, and 1.5%, along with crystalline microcellulose (MCC) contents of 0.4%, 0.6%, and 0.8%. The impact of cellulose microfiber and crystalline microcellulose on compressive strength, flexural tensile strength, mineralogy, and microstructure of cementitious composites was evaluated. The gradual increase in the combined additions of cellulose microfiber and crystalline microcellulose led to a reduction in mechanical properties. The diffraction patterns of the FC-MCC cellulose-added composites were similar to those of Portland cement composites without additives. The combinations of FC 0.5-MCC 0.4, FC 1.0-MCC 0.4, and FC 0.5-MCC 0.6 contents promoted a higher degree of hydration, resulting in superior compressive strength performance compared to cementitious composites without these materials.

Effect of Strengthening Mechanism of Alkali Curing on Mechanical Properties of Fly Ash Lightweight Aggregates and Its Concrete.

The low hydration degree of fly ash in Fly Ash Unburned Lightweight Aggregate (FULA) is not conducive to the development of the mechanical properties of lightweight aggregates and their concrete. In this paper, FULA was immersed in an alkaline solution with the purpose of improving the mechanical properties of FULA and its concrete. Firstly, FULA was prepared using fly ash as the main raw material. The effect of the alkaline solution type and concentration on the basic properties of FULA was studied. Then, lightweight aggregate concrete was prepared using FULA as a coarse aggregate. The role of the aggregate category and water-cement ratio in the mechanical properties of concrete was analyzed. Finally, the effect of alkali curing on the interfacial transition zone of concrete was tested by combining an electron microscope and microhardness tester. Based on this, the strengthening mechanism of alkali curing on the mechanical properties of concrete was proposed. The results show that alkali curing can effectively improve the mechanical properties of FULA and its concrete. The microhardness of the interfacial transition zone of alkali curing FULA concrete is significantly higher than that of the cementite matrix, and the closer the aggregate, the higher the microhardness. The fundamental reason for this is that alkali curing improves the hydration degree of fly ash.

Developments of the UralNIIstrom Institute in the field of technologies and equipment for enrichment of vermiculite ores and production of expanded vermiculite

Vermiculite deposits are a heterogeneous array of micaceous minerals of varying degrees of hydration with a significant number of host rocks.The development of technology and equipment for both the enrichment of vermiculite ores and for the swelling of vermiculite and hydrosludes should be carried out taking into account their mineralogical features and the composition of the host rocks. The UralNIIstrom Institute has developed a series of installations for the enrichment of vermiculite ores and the production of expanded vermiculite. The developed installations are successfully operated in the Russian Federation/ and abroad.

Relationship Between Expansion and Strength of Cement Paste with CaO-Based Expansive Agent.

In order to explore the intrinsic relationship between the expansion and strength of cementitious materials with CaO-based expansion agent (CEA), the effects of CEA on the expansion rate, strength, microstructure, and hydration products of cement paste were studied. The interaction mechanism between the expansion rate and compressive strength of cement paste with CEA was discussed. The results show that the addition of CEA increases the expansion rate, porosity, and hydration degree of cement paste while reducing the compactness and compressive strength of cement paste. As the CEA dosage increases, the expansion rate of cement paste gradually increases. During the expansion of cement paste, microcracks may occur. The larger the expansion rate, the more microcracks there are, and the compressive strength decreases linearly with the increase in the expansion rate. When the CEA dosage is the same, the expansion rate of cement paste gradually increases with the increase of mineral admixture content, and the expansion rate decreases linearly with the increase of compressive strength.

Failure Behavior of Nano-Metakaolin Concrete Under Splitting Tension Based on Digital Image Correlation Method.

Nano metakaolin (NMK) has attracted considerable interest for its potential to improve the durability of cementitious materials. However, the effect of NMK on the splitting tensile performance of concrete has not been systematically investigated. This study investigates the splitting tensile performance of NMK concrete and analyzes its failure behavior under splitting load. Different NMK dosages (0%, 1%, 3%, 5%, and 7%) were considered, and splitting tensile tests were conducted. The crack propagation process, crack width, and crack growth rate on the surface of NMK concrete during the splitting tensile test are analyzed using the Digital Image Correlation (DIC) method. The mechanisms by which NMK affects the splitting tensile performance of concrete were examined using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and Thermogravimetric Analysis (TG). The results indicate that the incorporation of NMK enhances the splitting tensile performance of concrete. Concrete with 5% NMK addition exhibited the highest splitting tensile strength, with an increase of 17.4% compared to ordinary concrete. NMK improved the cracking resistance and overall integrity under splitting tensile load. With 5% NMK addition, the surface crack length, width, and main crack propagation rate of the concrete decreased by 4.5%, 35.3%, and 29.6%, respectively. NMK contributed to a denser internal structure of the concrete, promoted the formation of C-S-H gel, and increased the degree of cement hydration. Moreover, a lower thickness and Ca/Si ratio of interfacial transition zone (ITZ) were observed in NMK concrete. The ITZ thickness and Ca/Si ratio of concrete with 5% NMK were reduced by 64.4% and 85.4%, respectively, compared to ordinary concrete. In summary, the influence mechanism of NMK addition on the splitting tensile strength and failure behavior of concrete is explored in this study, providing experimental data to support the application of NMK concrete in practical engineering.

Impact of Graphite-Associated Waste as a Sustainable Aggregate on UHPC Performance

In this study, graphite tailings produced in Luobei County, Heilongjiang Province, were used as a sustainable aggregate to replace river sand (0%, 25%, 50%, 75%, 100%) in UHPC for the preparation of ultra-high-performance concrete (UHPC). The experimental results showed that the incorporation of 75% graphite tailings caused a significant increase in the wet bulk density of UHPC mortar. The workability of UHPC decreased monotonically with the increase in graphite tailing substitution rate, and wet bulk density decreased by 28.42% with 100% graphite tailings (compared with no graphite tailings). The incorporation of 75% graphite tailings helped to improve the compressive and flexural strengths as well as the durability of UHPC. Compared with the UHPC without graphite tailings, the 28 d compressive and flexural strengths increased by 8.82% and 7.28%, respectively, and the chloride ion electrical flux decreased by 19.49%. XRD and thermogravimetric analysis data indicate that the incorporation of graphite tailings did not change the type of hydration and that the incorporation of graphite tailings helped to increase the degree of hydration within the UHPC matrix. MIP and SEM showed that 75% graphite tailings helped to reduce the porosity and the number of harmful pores inside the matrix. The 100% graphite tailings treatment replacing river sand decreased the economic cost of UHPC by up to 23.78%.

Influence of metakaolin on physical and mechanical properties of cement stone heat-resistant binder from mineral-technogenic raw materials of the Aral region

The results of studies of the influence of metakaolin obtained from kaolin of the Khodzhakul deposit on the process of formation of cement stone based on heat-resistant binder from mineral-technogenic raw materials of the Aral Sea region are presented. It has been established that metakaolin allows one to control the processes of hydration, setting and hardening of the cement mass. The high degree of hydration of aluminous cement in the presence of metakaolin provides porosity and sufficiently high compressive strength of the cement stone in the last 14‒28 days of hardening. Increasing the concentration of metakaolin in the cement mixture to 15 % affects not only the process of liquefying the cement mortar, reducing the setting and hardening time of the cement mass, but also increases the compressive strength of the cement stone. New formations of hydration products have been studied.

Evaluating the Effects of Laser Treatments on Visible Changes in the Photoaging Process of the Skin Using Specialized Measuring Devices.

Background/Objectives: The skin is the largest organ of the human body and is exposed to the aging process (not only chronological aging, but also photoaging). One of the methods used to correct visible skin changes due to photoaging is lasers. The aim of this study was to objectively evaluate the effect of Q-switched laser treatments on visible changes in the photoaging process among women using specialized measuring devices-ultrasound and Courage & Khazaka. Methods: The study included 36 women with visible signs of photoaged skin. The women were given a series of three treatments with a Fotona QX MAX fractional head laser. Both before and after the treatment, the women were examined for selected skin parameters with the help of specialized measuring devices such as Courage & Khazaka and skin ultrasound. Skin firmness and elasticity, the degree of hydration, TEWL and HL TOTAL levels, and MEP and HEP skin echogenicity were taken into account. The obtained results were tabulated and statistically analyzed. Results: Statistically significant differences were noted for parameters representing skin elasticity R2 [p = 0.0210] and R7 [p = 0.0302], TEWL [p = 0.0152] and HL TOTAL [p = 0.0367] on the forehead, and HL TOTAL [p = 0.0450] on the cheek. In addition, statistically significant differences were observed in the MEP/TP parameter on the forehead and cheek [p = 0.0236, 0.0475, respectively] and HEP/TP in the forehead area [p = 0.0367]. Conclusions: Q-switched laser treatments have a positive effect on the condition of women's skin. Therapy with this laser reduces the visible changes in the photoaging process in the face.

Effect of a novel negative temperature early-strength agent in improving concrete performance under varying curing temperatures

This study investigates the effect of a novel negative temperature early-strength agent (NEA) in enhancing concrete performance under varying curing temperatures, with a discussion on the underlying mechanism through analysis of hydration products and microstructure.The results indicate NEA markedly accelerates early cement hydration, reduces setting time, and enhances compressive strength. Moreover, the efficacy of NEA is more pronounced at lower temperatures. With an optimal dosage of 3%, the incorporation of NEA leads to a remarkable 285.9% increase in compressive strength at 28 days under -5°C curing temperature. Despite accelerating cement hydration can induce increased chemical shrinkage, NEA effectively mitigates early freezing expansion under negative temperature and significantly diminishes chloride ion permeability. Higher temperatures facilitate early cement hydration but also compromise long-term hydration continuity. Consequently, the highest hydration degree and loweast porosity are observed at 28 days under 5°C curing temperature. NEA's air-entraining component introduces numerous superfine pores into the paste, augmenting early pore volume while optimizing pore structure. As the early-strength component fosters hydration, these pores undergo further filling and refinement, ultimately reducing the total pore volume at 28 days. This study provides insights into optimizing concrete performance in cold environments.

Fatigue Flexural Properties of Graphite Tailings Concrete Modified with Basalt Fiber

Graphite tailings were solid wastes which were large and difficult to deal with. In order to promote the utilization of graphite tailings and reduce the consumption of natural river sand, this paper replaced part of the natural river sand with graphite tailings and added environmentally friendly green fibers for modification to jointly prepare basalt fiber modification graphite tailings concrete. In order to encourage the adoption of graphite tailings concrete during the construction of roads, it was crucial to fully understand the fatigue and flexural properties of concrete. Through experimental research, this paper analyzed the effects of graphite tailings and basalt fiber mixing on the flexural mechanical properties and fatigue life of concrete, and used solid-state 29Si nuclear magnetic resonance, back scattered electron microscope, and nanoindentation to investigate the interface transition zone. The results indicated that the most effective combination was concrete with a 20% graphite tailings substitution rate and 0.1% basalt fiber by volume, whose flexural strength could be increased by up to 19.10% compared with PC, and when the stress level was 0.6, the fatigue life characteristic value of it was 3.94 times than that of PC. Combined with the results of the microscopic testing, it could be demonstrated that an appropriate amount of graphite tailings could promote the absorption of the Al element, increase the chain length and strength of C-S-H gel, and thereby increase the total content of C-S-H gel. Compared with PC, when the graphite tailings substitution rate was 20%, the hydration degree increased by up to 37.00%, and the total C-S-H gel content also rose by 12.01%. In addition, the admixture of an appropriate amount of graphite tailings would reduce the pores and micro-cracks in the interface transition zone, make the interface transition zone denser, increase its elastic modulus, and reduce the width. At 20 percent of the graphite tailings substitution rate, compared with PC, the minimum width could be reduced by 33.33%, and the elasticity modulus improvement range could reach 33%–40%. These further proved that basalt fiber-modified graphite tailings concrete could strengthen its flexural properties and fatigue life, as well as its feasibility in road engineering applications.

Improved chloride binding capacity in sustainable metakaolin blended seawater cement mortar: Effect of external alternative electric field

Seawater is a promising substitution of fresh water in concrete production to relieve the resource crisis, especially for the concrete fabricated in harsh environment with less freshwater supply, while the excessive chloride ion (Cl-) in seawater may induce severe durability issue. In this work, metakaolin (MK) was used as supplementary cementitious material to prepare seawater cement mortar (SWCM), and ohmic heating (OH) curing was utilized to fabricate MK-SWCM at -20 °C by creating high temperature curing condition, with conductive carbon fibers (CFs) as electrical reinforcement media. The CFs fraction was numerically and experimentally obtained as 1.0 vol%, the electrical resistivity, electric voltage and curing temperature change during OH process was disclosed. Results showed that MK inclusion and OH curing both contributed to enhancing the Cl- binding capacity with higher hydration degree and denser pore structure. To be specific, OH cured SWCM with 10% MK content endowed the Cl- binding ratio of 35.4%, meeting the increase of 97.8% compared to that of room temperature cured SWCM with no MK addition. Moreover, the mechanical strengths were further proven excellent for winter production in cold environment, which were all above 60 MPa with the aid of OH curing. A systematical analysis was conducted to roundly clarify the benefits for MK-SWCM fabrication in cold region from the aspects of Cl- binding capacity efficiency, environmental benefits and mechanical strength.

Microstructural evolution and degradation mechanisms of tricalcium silicate and tricalcium aluminate composite pastes under sulfate exposure

Sulfate attack precipitates instability and degradation within calcium silicate (aluminate) hydrate (C-(A)-S-H) gel, the primary binding phase in cementitious materials. This degradation intricately correlates with the clinker phase composition, particularly the ratios of tricalcium silicate (C3S) and tricalcium aluminate (C3A). In this study, C3S and C3A were synthesized through solid-state sintering to create C3S-C3A pastes. The research aimed to examine the impact of varying C3A substitution levels and Na2SO4 exposure durations on the microstructure and performance of these composite pastes. The findings reveal that C3A markedly accelerates both the early hydration kinetics and the overall hydration degree of C3S within the C3S-C3A system, with this effect becoming more pronounced with increasing C3A content. Furthermore, the inclusion of C3A elevates the Al[4]/Si ratio, mean chain length (MCL), and Ca/Si of the C-S-H gel. This leads to an increase in the overall porosity of the composite matrix while simultaneously diminishing its chloride-binding capacity. Exposure to Na2SO4 disrupts the incorporation of Al3+, released during C3A hydration, into the bridging sites of the C-S-H structure, causing a decrease in the Al[4]/Si of the C-(A)-S-H gel. The leached aluminum subsequently reacts with SO42- to form ettringite and other deleterious compounds. Additionally, Na2SO4 exposure induces a significant reduction in the Ca/Si within the composite pastes, with the magnitude of decalcification inversely proportional to the initial Ca/Si—implying that higher C3A content exacerbates the decalcification process. During the process of sulfate attack, the formation of gypsum and AFt complicates the pore structure of the matrix, providing more adsorption sites for the binding of Cl-.

Cross-scale time-varying prediction model of oxygen diffusion in unsaturated concrete

The oxygen diffusion coefficient is a key factor in predicting the service life of reinforced concrete structures. However, cross-scale time-varying predictive modelling of oxygen diffusion in unsaturated concrete has not been carried out. In this study, firstly, the concrete pore structure is simplified as the Menger sponge model, and the effects of pore parameters, hydration degree and fractal dimension on the five oxygen diffusion mechanisms in unsaturated concrete are considered; Secondly, the pore parameters, degree of hydration and fractal dimension are analyzed with respect to time, taking into account the time-varying pore microstructure of concrete; Lastly, a cross-scale time-varying prediction model for oxygen diffusion in concrete under unsaturated state is established that includes the time-varying parameters and takes into account the five diffusion mechanisms; Finally, a cross-scale time-varying prediction model of oxygen diffusion in concrete under unsaturated condition is established with time-varying parameters and considering five diffusion mechanisms. The results show that the oxygen diffusion coefficient decreases with the increase of hydration degree, water saturation, and fractal dimension. This study will provide a theoretical basis for predicting the life of reinforced concrete in the marine environment.

Mechanical-Chemical Activation of Cement-Ash Binders to Improve the Properties of Heat-Resistant Mortars.

The article demonstrates the effectiveness of the mechanochemical activation of a cement-ash binder by increasing the specific surface area of the ash and introducing a sodium fluorosilicate additive (Na2SiF6). It has been experimentally proved that the introduction of a Na2SiF6 additive makes it possible to increase the degree of cement hydration, as well as the intensity of free CaO binding when heating the cement-ash binder in the range of 500 °C to 800 °C. Mechanochemical activation prevents a decrease in the strength of the preheated cement-ash binder. During cyclic heating and cooling of slag mortars based on the activated cement-ash binder, an improvement in the set of basic properties was observed: compressive strength, flexural strength, water absorption, dynamic modulus of elasticity, and conditional elongation. Experimental design was carried out to obtain experimental-statistical models of mortar properties based on composition, heating temperature, and number of heating-cooling cycles. These models made it possible to develop quantitative relationships for predicting mortar properties at elevated temperatures and to rank the factors in order of importance. The optimal values for the dosage of fly ash, sodium silicofluoride additive, and the binder's specific surface area were established. It was demonstrated that the activator has a positive effect on the thermal deformation of mortars.

Utilizing spodumene slag as a supplementary cementitious material: A quantitative study

This study investigates the potential of spodumene slag (SPS) as a supplementary cementitious material (SCM). Firstly, the comprehensive characterization results show that SPS consists of quartz, gypsum, calcite, lazurite, and alumino-silicates, with 34 % amorphous content. Next, the hydration characterization indicates that SPS has limited self-cementing properties; however, it inhibits the initial dissolution of C3S, C3A, and C4AF due to the gypsum. This inhibition for C3S is counteracted by the dilution effect of SPS. Over time, the hydration degrees of the clinker phases improve as SPS provides additional nucleation sites and retains more free water for cement hydration. Additionally, thermodynamic modelling was established and validated by experimental data to capture the reaction process and phase changes. AFt forms in all systems, but AFm phases decrease and disappear at 40 % and 50 % SPS levels. Engineering tests reveal that 50 % SPS addition extends initial setting time by 60 %, and reduces fluidity by 20 %. Compressive strength remains acceptable up to 20 % SPS replacement, with an activity index of more than 80 %. Overall, SPS shows potential as a supplementary cementitious material, but careful adjustment of replacement levels is essential to minimize its disadvantages.

A Study on the Mechanism by Which Graphene Oxide Affects the Macroscopic Properties and Microstructure of Abrasion-Resistant Ultra-High-Performance Concrete (UHPC)

To further enhance the abrasion resistance of UHPC in demanding abrasion environments, this study investigated the effects of graphene oxide (GO) on the workability, mechanical properties, and abrasion resistance of UHPC. Utilizing 27Al Nuclear Magnetic Resonance (NMR), 29Si NMR, microhardness, and BET analysis, the study analyzed the mechanisms through which GO influences UHPC’s microstructure in terms of abrasion resistance. Additionally, molecular dynamics simulations were employed to examine the mechanisms by which GO enhances UHPC’s abrasion resistance at the nano and micron scale. The findings show that an optimal amount of GO can improve the mechanical properties and abrasion resistance of UHPC. When 0.03% of GO (by cementitious material mass) was incorporated, the impact on workability was minimal, yet compressive strength increased by approximately 1.80%, flexural strength by 3.02%, impact wear resistance by 1.78%, the abrasion loss rate decreased by 10.01%, ultimate impact energy increased by 1.76%, and the toughness index improved by 10.10%. GO enhances abrasion-resistant UHPC primarily by increasing hydration, refining pore structure, and improving the microstructure of the interfacial transition zone. While GO increases the hydration degree of the UHPC matrix, it does not alter the silicate chain in C-A-S-H gels within the paste. Additionally, the incorporation of graphene oxide can refine the pore structure of the UHPC cement paste and improve the microstructure of the interfacial transition zone (ITZ) between the aggregate and the cement paste. The molecular dynamics simulation reveals that, under abrasive forces, GO forms strong, stable chemical bonds with the C-A-S-H base atoms, significantly enhancing the abrasion resistance of C-A-S-H.

Selective Synthesis of Double-Layer Nanosheets Via Layered Ruthenic Acid with a Staged Structure

Noble metal oxide nanosheets are attractive electrode materials owing to their high surface area as well as electrical conductivity and electrochemical stability. Noble metal oxide nanosheets have been studied as materials for electrochemical capacitors and electrocatalysts, focusing on factors such as composition, sheet size, and crystal structure.1 Noble metal oxide nanosheets are commonly obtained as single-layer nanosheets through exfoliation of pristine layered materials by intercalation of bulky organic species into each interlayer to sufficiently weaken the interactions between layers. Since the properties of nanosheets are modulated according to the number of layers, the selective synthesis of multi-layered nanosheets can be a new strategy for nanosheet-based material design. For selective synthesis of multi-layered nanosheets, site-selective intercalation of layered materials forming superlattices is required. This can limit the interlayers where exfoliation occurs.2–4 We have previously reported that the dehydration of proton-exchanged layered potassium ruthenate proceeds layer-by-layer, resulting in a stage 2 structure with alternating hydrous and anhydrous interlayers.5,6 The two types of interlayers in layered ruthenic acid with staged structure should show different reactivity for intercalation because of different degrees of hydration. In this study, we attempted to develop a site-selective intercalation of organic molecules into layered ruthenic acid with staged structure for the selective synthesis of double-layer ruthenic acid nanosheets. Hydrous layered ruthenic acid (Stage 1-HRO) was synthesized by slight modification of previous literature methods.5,6 Stage 1-HRO was partially dehydrated at a controlled humidity condition to form layered ruthenic acid with staged structure (Stage 2-HRO). The XRD pattern of Stage 2-HRO showed a basal spacing of d = 1.24 nm which is larger than that before dehydration (d = 0.786 nm). This peak can be attributed to the superlattice structure with alternating hydrous and anhydrous interlayers, suggesting the formation of a stage 2 structure. For ion exchange, Stage-1 HRO and Stage-2 HRO were respectively added to an aqueous solution containing CTA+ (cetyltrimethylammonium). The ion exchanged Stage-2 HRO (Stage 2-HRO + CTA+) shows a larger basal spacing of d = 2.72 nm and its high-order diffractions are visible. The value of d = 2.72 nm is within the range of the anticipated structure when CTA+ intercalates only in hydrous interlayers while maintaining a stage 2 structure. The ion exchanged Stage 1-HRO (Stage 1-HRO + CTA+) shows a basal spacing of d = 2.49 nm, which was smaller than the basal spacing of Stage 2-HRO + CTA+. The ion exchanged samples were dispersed in organic solvent to initiate exfoliation into nanosheets. The height of nanosheets obtained from Stage 1-HRO + CTA+ was approximately 1.3 nm, while that obtained from Stage 2-HRO + CTA+ was approximately 1.8 nm. Since the crystallographic thickness of single-layered ruthenic acid nanosheets was approximately 0.5 nm, the difference in thickness is consistent with single-layer ruthenic oxide sheets. Considering the presence of CTA+ on the surface of nanosheets, double-layer ruthenic oxide nanosheets were exfoliated from Stage 2-HRO + CTA+. These results suggest that preparation of double-layer ruthenium oxide nanosheets is facilitated by controlling the interlayer environment of layered ruthenic acid utilizing the staging phenomenon. References W. Sugimoto and D. Takimoto, Chem. Lett., 50, 1304 (2021).T. Nakato, D. Sakamoto, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 65, 322 (1992).M. Stöter, B. Biersack, S. Rosenfeldt, M. J. Leitl, H. Kalo, R. Schobert, H. Yersin, G. A. Ozin, S. Förster and J. Breu, Angew. Chem. Int. Ed., 54, 4963 (2015).F. Chen, W. Zhou, L. Jia, X. Liu, T. Sasaki and R. Ma, Chem Catal., 2, 867 (2022).W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami and Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003).K. Fukuda, H. Kato, J. Sato, W. Sugimoto and Y. Takasu, J. Solid State Chem., 182, 2997 (2009).Z. Hu, G. He, Y. Liu, C. Dong, X. Wu and W. Zhao, Appl. Clay Sci., 75–76, 134 (2013). Figure 1

Exploring the Impact of Excess Cations in Acidic CO2 Reduction Reaction

To anticipate high performance in the electrocatalytic reactions, a comprehensive understanding of the electric double layer (EDL) is essential. Experimental, spectroscopic, and computational studies of the EDL have been reported for understanding the performance in electrocatalytic reactions such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR). Notably, in the CO2RR, previous studies have revealed the accumulation of cations near the outer Helmholtz plane (OHP) significantly has an impact on the reaction performance, product selectivity, and partial current density. The presence of these cations induces various effects, such as creating a strong electric field, altering local pH levels, stabilizing the intermediates, and specific adsorption. However, unraveling the sole cation effect remains challenging due to the system's complexity and hierarchical characteristics. Moreover, experiments predominantly conducted under favorable conditions for understanding the electric field and stabilization effects have left the specific adsorption effect relatively unexplored. Specific adsorption involves direct coordination with the electrode at the inner Helmholtz plane (IHP), with the degree determined by catalyst type and electrolyte conditions. Previous studies have highlighted the significant impact of specific adsorption on current density and intermediate stabilization, with potassium (K+) and cesium (Cs+) cation exhibiting the most pronounced effect owing to their minimal hydration degree compared to the lithium (Li+) and sodium (Na+).Acidic CO2RR has recently garnered attention for its high carbon efficiency (CE) and energy efficiency (EE). However, the abundance of hydronium ions can lead to a favorable occurrence of HER over CO2RR due to its facile protonation. To mitigate this challenge, excess cations have been employed to suppress the hydronium ion migration and enhance the performance of the CO2RR, which means accumulated cation layer at the OHP can suppress the HER and stabilize the intermediates of the CO2RR simultaneously. Meanwhile, in the excess cation condition, adsorbed cations can be dominant on the electrode originated from the excess cations, which is not investigated intensively. For the better performance of the electrocatalytic reactions in the acidic condition, we need to elucidate the EDL formed in the presence of the excess cations.In here, we investigated the electrode-electrolyte interface in the different cation species during the acidic CO2RR through the attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS), which can give the local information such as the adsorbed species on the metal and free species near the electrode. We confirmed the different product distribution and interface depending on the cation species, especially in the excess cations (1 M M+, M = Li, K, Cs). Specific adsorption in the presence of the excess cations can alter the product distribution, and it differs from the low cation concentration (0.1 M M+, M = Li, K, Cs). In final, to clarify the effect originated from the excess cations, we confirmed the interface on the copper and silver, which major products are C2+ and C1, respectively.