Progress on the mechanisms of Ru-based electrocatalysts for the oxygen evolution reaction in acidic media

Water electrolysis using proton-exchange membranes is one of the most promising technologies for carbon-neutral and sustainable energy production.Generally,the overall efficiency of water splitting is limited by the oxygen evolution reaction(OER).Nevertheless,a trade-off between activity and stability exists for most electrocatalytic materials in strong acids and oxidizing media,and the development of efficient and stable catalytic materials has been an important focus of research.In this view,gaining in-depth insights into the OER system,particularly the interactions between reaction intermediates and active sites,is significantly important.To this end,this review introduces the fundamentals of the OER over Ru-based materials,including the conventional adsorbate evolution mechanism,lattice oxygen oxidation mechanism,and oxide path mechanism.Moreover,the up-to-date progress of representative modifications for improving OER performance is further discussed with reference to specific mechanisms,such as tuning of geometric,electronic structures,incorporation of proton acceptors,and optimization of metal-oxygen covalency.Finally,some valuable insights into the challenges and opportunities for OER electrocatalysts are provided with the aim to promote the development of next-generation catalysts with high activity and excellent stability.

CO selective methanation in hydrogen-rich gas mixtures over carbon nanotube supported Ru-based catalysts

Series of carbon nanotube supported Ru-based catalysts were prepared by impregnation method and applied successfully for complete removal of CO by CO selective methanation from H2-rich gas stream conducted in a fixed-bed quartz tubular reactor at ambient pressure. It was found that the metal promoter, reduction temperature and metal loading affected the catalytic properties significantly. The most excellent performance was presented by 30 wt% Ru-Zr/CNTs catalyst reduced at 350 ℃. Since it decreased CO concentration to below 10 ppm from 12000 ppm by CO selective methanation at the temperature range of 180-240 ℃, and kept CO selectivity higher than 85% at the temperature below 200 ℃. Characterization using XRD, TEM, H2-TPR and XPS suggests that Zr modification of Ru/CNTs results in the weakening of the interaction between Ru and CNTs, a higher Ru dispersion and the oxidization of surface Ru. Amorphous and high dispersed Ru particles with small size were obtained for 30 wt% Ru-Zr/CNTs catalyst reduced at 350 ℃, leading to excellent catalytic performance in CO selective methanation.

Mo doped Ru-based cluster to promote alkaline hydrogen evolution with ultra-low Ru loading

Green hydrogen energy developed through electrochemistry is one of the solutions to current energy problems.The less noble metal ruthenium(Ru)plays an important role in alkaline electrocatalytic hydrogen evolution reaction(HER)as an effective electrocatalyst.Nevertheless,the high cost(>110 RMB per gram)hinders the large-scale application of Ru in industrial hydrogen production.Moreover,the strong adsorption of OH*in-termediates over Ru limits the electrocatalytic performance in alkaline HER.Here,we report the Mo-doped Ru nanocluster embedded on N-doped carbon framework(RuMo/NC)as alkaline HER catalyst,which shows excellent catalytic performance with an overpotential of 24.2 mV to reach 10 mA cm-2 with only 0.4 wt%o of Ru,much lower than that of most reported Ru-based catalysts.DFT calculations reveal the introduction of Mo has improved the activity by alleviating the poisoning effect of OH*over Ru in HER.Through fully utilizing Ru in the catalyst,this work marks a step forward in the development of Ru-based catalysts in alkaline HER.

Ru-based catalysts for efficient CO_(2) methanation:Synergistic catalysis between oxygen vacancies and basic sites

The fundamental insights of the reaction mechanism,especially the synergistic effect between oxygen vacancies and basic sites,are highly promising yet challenging for Ru-based catalysts during carbon dioxide(CO_(2))methanation.Herein,a series of Rubased catalysts were employed to study the mechanism of CO_(2) methanation.It is found that Ru/CeO_(2) catalyst exhibits a much higher CO_(2) conversion(86%)and CH4 selectivity(100%),as well as excellent stability of 30 h due to the existence of abundant oxygen vacancies and weak basic sites.Additionally,the in-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and density functional theory(DFT)calculations reveal that the formate formation step dominated the hydrogenation route on Ru/CeO_(2) catalyst,and the b-HCOO^(*)could be the key intermediate due to b-HCOO^(*)is more easily hydrogenated to methane than m-HCOO^(*).The systematic study marks the significance of precise tailoring of the synergistic relationship between oxygen vacancies and basic sites for achieving the desired performance in CO_(2) methanation.

Regulating the coordination environment of Ru single-atom catalysts and unravelling the reaction path of acetylene hydrochlorination

In this work,DFT calculations were used firstly to simulate the nitrogen coordinated metal single-atom catalysts(M-N_(x)SACs,M=Hg,Cu,Au,and Ru) to predict their catalytic activities in acetylene hydrochlorination.The DFT results showed that Ru-N_(x)SACs had the best catalytic performance among the four catalysts,and Ru-N_(x)SACs could effectively inhibit the reduction of ruthenium cation.To verify the DFT results,Ru-N_(x)SACs were fabricated by pyrolyzing MOFs in-situ spatially confined metal precursors.The N coordination environment could be controlled by changing the pyrolysis temperature.Catalytic performance tests indicated that low N coordination number(Ru-N_(2),Ru-N_(3))exhibited excellent catalytic activity and stability compared to RuCl_(3)catalyst.DFT calculations further revealed that Ru-N_(2)and Ru-N_(3)had a tendency to activate HCl at the first step of reaction,whereas Ru-N4tended to activate C_(2)H_(2).These findings will serve as a reference for the design and control of metal active sites.

Highly dispersed Ru nanospecies on N-doped carbon/MXene composite for highly efficient alkaline hydrogen evolution

Hydrogen has emerged as a promising environmentally friendly energy source. The development of lowcost, highly active, stable, and easily synthesized catalysts for hydrogen evolution reactions(HER) remains a significant challenge. This study explored the synthesis of nitrogen-doped MXene-based composite catalysts for enhanced HER performance. By thermally decomposing RuCl_(3) coordinated with melamine and formaldehyde resin, we successfully introduced nitrogen-doped carbon(N–C) with highly dispersed ruthenium(Ru) onto the MXene surface. The calcination temperature played a crucial role in controlling the size of Ru nanoparticles(Ru NPs) and the proportion of Ru single-atom(Ru SA), thereby facilitating the synergistic enhancement of HER performance by Ru NPs and Ru SA. The resulting catalyst prepared with a calcination temperature of 600℃, Ti_(3)C_(2)T_x-N/C-Ru-600(TNCR-600), exhibited exceptional HER activity(η10= 17 m V) and stability(160 h) under alkaline conditions. This work presented a simple and effective strategy for synthesizing composite catalysts, offering new insights into the design and regulation of high-performance Ru-based catalysts for hydrogen production.

Ru-doped functional porous materials for electrocatalytic water splitting

Electrolytic water splitting(EWS)is an attractive and promising technique for the production of hydrogen energy.Nevertheless,the sluggish kinetic rate of hydrogen/oxygen evolution reactions leads to a high overpotential and low energy efficiency.Up to date,Pt/Ir-based nanocatalysts have become the state-of-the-art EWS catalysts,but disadvantages such as high cost and low earth abundance greatly limit their applications in EWS devices.As an attractive candidate for the Pt/Ir catalysts,series of Ru-based nanomaterials have aroused much attention for their low price,Pt-like hydrogen bond strength,and high EWS activity.In particular,Ru-doped functional porous materials have been becoming one of the most representative EWS catalysts,which can not only achieve the dispersion and adjustment for active Ru sites,but also simultaneously solve the problems of mass transfer and catalytic conversion in EWS.In this review,the design and preparation strategies of Ru-doped functional porous materials toward EWS in recent years are summarized,including Ru-doped metal organic frameworks(MOFs),Ru-doped porous organic polymers(POPs),and their derivatives.Meanwhile,detailed structure–activity relationships induced by the tuned geometric/electronic structures of Ru-doped functional porous materials are further depicted in this review.Last but not least,the challenges and perspectives of Ru-doped functional porous materials catalysts are reasonably proposed to provide fresh ideas for the design of Ru-based EWS catalysts.

Enriching the surface oxygen as efficient anchoring site of highly dispersed Ru for enhanced hydrogenolysis activity

While supported-noble-metal catalysts have been widely investigated in hydrotreating reactions,a crucial issue that the catalytic system is still confronted with is developing an efficient approach to gain the high dispersion of noble metals under reducing conditions.In this work,Ru was supported on two MnOx with different specific surface areas(SSAs),and a much higher dispersion of Ru(83%,in contrast to 42%of the other one)was surprisingly observed over MnO with much lower SSA(around one-third of the other one).A suite of complementary characterizations demonstrates that,compared with the catalyst with high SSA(Ru/MnO-H),the MnO in the one with lower SSA(Ru/MnO-L)contains enriched surface oxygen that creates more abundant sites and bears stronger strength to anchor Ru species,mitigating the aggregation of Ru under reducing condition.This not only enriched active sites(i.e.,exposed Ru),but also created a more electron-deficient Ru domain and thus enhanced the redox property of the surface,leading to the lower barrier for C–O bond hydrogenolysis.In the hydrogenolysis of diphenyl ether,Ru/MnO-L exhibited significantly enhanced activity(i.e.,6 folds of Ru/MnO-H)and high stability.This work provides an approach to regulate the surface chemistry of support for the high dispersion of supported metal.

Effect of rare earth elements(La,Y,Pr)in multi-element composite perovskite oxide supports for ammonia synthesis

A series of BaCe0_(3)modified with different rare earth elements(La,Y,Pr)were synthesized by coprecipitation and calcination and the effect of rare earth elements for catalytic ammonia synthesis under mild conditions was studied.The ammonia synthesis performance tests show that 2.5%Ru/BaCe_(0.9)La_(0.1)O_(3-δ)catalyst(All the percentages of Ru in this article are in mass fraction)exhibits the highest ammonia synthesis rate(34 mmol/(g·h))at 3 MPa,450℃,and no sign of deactivation after 100 h of reaction.H_(2)-TPR and XPS analyses indicate that the introduction of La increases the amount of oxygen vacancies of the catalyst,which is beneficial to increasing the electron density of Ru surface.HRTEM analysis shows that the Ru particle size is reduced greatly after La is introduced,which facilitates the catalyst generating more Bs-type sites(active sites of Ru species for N=N dissociation).CO_(2)-TPD analysis indicates that BaCe_(0.9)La_(0.1)O_(3-δ)has stronger basicity,which promotes electrons transfer from support to Ru.This work provides an effective method for design and synthesis of Ru-based multi-element composite perovskite oxide catalysts.

Biochar aerogel-based electrocatalyst towards efficient oxygen evolution in acidic media

The controllable synthesis of oxygen evolution reaction(OER)electrocatalyst is an urgent need to advance the develop-ment of sustainable energy conversion and storage.However,the OER efficiency in acidic media is seriously hindered by slow reaction kinetics.The traditional acidic OER electrocatalysts are more prone to be oxidized and corroded as results of unstable carrier structures and variable electronic states of active species.Herein,a high-performing biochar aerogel(BA)based electrocatalyst were realistically designed and synthetized via joint utilization of the terrestrial lignin and seaweed polysaccharide as carbon sources.Originating from the induction effect of"egg-box"structure in alginate and the self-template effect of lignosulfonate,the BA decorated with Ru/RuS_(2)particles was synthesized triumphantly.The as-synthesized electrocatalyst required a low overpotential of 228 mV to attain 10 mA cm^(−2)in 0.5 M H_(2)SO_(4)and exhibited a good stability for over 12,000 s.The good activity was strongly dependent on the assembled unique two-dimensional/three-dimensional(2D/3D)channels in carbon aerogels.Notably,the numerous defective sites at carbon could strongly interact with the Ru/RuS_(2)heterojunction for remarkably enhancing the catalytic activity and stability of whole catalytic system in acidic media.This work puts forward a novel and effective strategy towards the enhancement of the acidic OER process by rational regu-lations of the BA and the coupling effect in micro-interface.

钌基单原子和团簇催化剂在电催化反应中的竞争和协同效应

单原子和团簇催化剂在电催化领域,尤其是可持续能源存储和转化领域的重要性,得到越来越多地认可.单原子催化剂具有低金属负载和高原子利用效率的优点,但由于其表面自由能常常使得单个原子不稳定而发生聚集.团簇催化剂则因为其高原子利用率以及多样的活性位点,能够克服单原子催化剂在中间体吸附和活化等方面的局限性.钌基催化剂在电催化中有着十分重要的应用前景.然而,准确设计钌基单原子和团簇催化剂的几何和电子结构,并揭示它们之间的结构-性质关系,仍然面临着巨大的挑战.因此,我们对钌基催化剂进行了分类和比较(同源/异源),重点总结了钌基单原子和团簇在电催化领域的竞争和协同效应.近年来,钌基催化剂在析氢反应(HER)方面取得了显著进展,因此着重介绍钌基催化剂在HER中的应用,并涵盖了其他电催化反应、双功能反应(HER/OER、HER/HOR)和电化学有机反应.此外,本文还探讨了钌基单原子和团簇在HER过程中的催化机理.最后,我们指出了在复杂钌基催化剂的工业应用开发策略中所面临的挑战和前景.