| Hydrogen energy is considered as an ideal green energy in the future owing to the advantages of abundant resources,high combustion calorific value and zero pollution.Compared with other various ways of hydrogen production,electrocatalytic splitting of water has drawn much attention because of the characteristics of environmentally friendly process,high energy conversion efficiency,and high product purity.Platinum?Pt?is generally considered as the most advanced electrocatalyst for the hydrogen evolution reaction?HER?,however,its limited reserves and high cost have hindered its wide application in industry.As a result,the key to realize the application of hydrogen energy is to explore low-cost,efficient and stable catalysts for HER.Ruthenium?Ru?possesses a similar bond strength with hydrogen,and compared with other precious metals such as Pt,palladium?Pd?and iridium?Ir?,it has obvious cost advantages.For this reason,Ru-based HER catalysts are considered as an ideal replacement material for Pt-based catalysts.It is well known that carbon carriers are able to enhance the electron interaction between the active metal components,promote the electron transfer in the catalytic process,and improve the catalytic activity.Carbon dots?CDs?,a kind of zero-dimensional carbon material,are regarded as ideal catalyst carriers for their simple synthesis process and low cost.In addition,because of the excellent conductivity,CDs can be used as good electron donors and acceptors.Based on the above,we focused on the metal/CDs hybrid materials and prepared a series of Ru-based/CDs hybrid materials.Their electrocatalytic activity and mechanism were deeply analyzed.The main research contents were as follows:?1?A novel biomass derived HER catalyst was designed via hydrothermal process using garlic as carbon and nitrogen source,where ruthenium dots were loaded on the self-crosslinking carbon dots?Ru@SC-CDs?.By changing the ratio of Ru dots to SC-CDs,the optimum ratio of metal to carbon was explored.Especially,Ru@SC-CDs 2:10showed excellent HER activity at all p H values,with a small overpotential?59 m V?at current density of 10 m A cm-2 in 0.5 M,and exhibits a small overpotential?29m V?in 1 M KOH and 66 m V in 1 M PBS at current density of 10 m A cm-2,which is comparable to that of the 20 wt%commercial Pt/C and other reported HER electrocatalysts.Besides,the catalyst shows outstanding stability.It was noteworthy that the stability of Ru@SC-CDs at all p H values outperforms commercial Pt/C catalysts.The chronoamperometric response for Ru@SC-CDs exhibits slight decrease even after 100 h.The calculation of density functional theory revealed a synergetic effect between Ru dots and SC-CDs that is responsible for the outstanding HER catalytic activity as well as the stability of Ru@SC-CDs.?2?Despite of outstanding activity of Ru@SC-CDs,the content of Ru was still too high.In order to reduce the content of Ru,we introduced cheap transition metals such as Ni,Mn,Cu by using hydrothermal method and thermal treatment.Carbon quantum dots?CQDs?were used to assemble with bimetallic nanoparticles Ru-M?M=Ni,Mn,Cu?to prepare highly efficient and stable electrocatalysts Ru M/CQDs for hydrogen evolution reaction at all p H valus.As a proof-of-concept example,Ru Ni/CQDs only needed overpotentials of 13 m V?1 M KOH?,58 m V?0.5 M?and 18 m V?1 M PBS?for the HER to achieve a current density of 10 m A cm-2,respectively.Notably,the loading of Ru was only 5.93?g cm-2.Besides,Ru Mn/CQDs and Ru Cu/CQDs exhibited similar excellent HER performance and outstanding cycling stability.DFT calculations revealed that Ni doping results in a moderate weakening of the hydrogen bonding energy of nearby surface Ru atoms,which played a critical role in improving the HER.Meanwhile,it also improved the interaction between metals,promoted electron transfer,and improved the performance of hydrogen evolution reaction.?3?In order to in-depth study of the effects of metal components in composite catalysts during the process of HER and simultaneously establish the relationship between catalyst activity center and its performance,we designed two different structural units—Ru single/dual atoms?S/DAs?and Ru S/DAs+Ru nanoclusters?NCs?by changing the pretreatment temperature of Tris?2,2-bipyridine?dichlororuthenium?II?hexahydrate.Especially,Ru S/DAs+Ru NCs showed excellent HER activity with a low overpotential of 10 m A cm-2?40 m V in 0.5 M,15 m V in 1 M KOH?.The synergistic effect of Ru S/DAs and Ru NCs not only enhanced the catalytic activity but also improved the stability compared to Ru S/DAs.?4?As an important part of carbon-based catalyst,carbon carrier has a significant effect on the catalytic activity of metal nanoparticles.In order to further explore the influence of HER performance between carbon carriers and metal?Ru?,citric acid and melamine were used as raw materials to obtain the N doped CDs with high crystalline,according to the mechanism of small molecule hydrothermal reaction to form polymer and the basis of amide dehydration condensation reaction between molecular compound.As a result,we prepared various of carriers including metal-organic framework,nanotubes,graphene,molecules,CDs and then combined them with Ruto get diverse Ru NPs at different carriers.Among them,CDs as carrier could realize the controllable preparation of Ru NPs both in size and dispersibility.Because of the combination between Ru NPs and CDs,the catalytic sites were effectively exposed,thereby improving the catalytic performance.Ru@CDs exhibited an excellent HER activity and great stability with a low overpotential of 22 m V in 1 M KOH at 10 m A cm-2.Not only the synergistic effect between CDs and Ru but also proper crystalline of Ru NPs were beneficial to the electron transfer between metals and carriers.Hence,CDs were considered as ideal carriers to achieve excellent activity and outstanding stability for HER. |
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