Surface modification of activated carbon with silver nanoparticles for electrochemical double layer capacitors

Jou nal o Ene gy S o age 54 (2022) 105367 A ailable online 28 July 2022 2352-152X/© 2022 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Resea ch pape s Su ace modi ica ion o ac i a ed ca bon wi h sil e nanopa icles o elec ochemical double laye capaci o s Am i a Jain a , * , Monika Michalska b , Angelika Zaszczy´ nska a , Pio Denis a a Ins i u e o Fundamen al Technological Resea ch, Polish Academy o Sciences, Pawi´ nskiego 5B, 02-106 Wa saw, Poland b Depa men o Chemis y and Physico-Chemical P ocesses, Facul y o Ma e ials Science and Technology, Vˇ SB-Technical Uni e si y o Os a a, 17. lis opadu 2172/15, 708 00 Os a a-Po uba, Czech Republic ARTICLE INFO Keywo ds: Supe capaci o Ac i a ed ca bon-sil e composi e Gel polyme elec oly e Elec ochemical s udies ABSTRACT In he p esen wo k, we epo he syn hesis o su ace modi ied ac i a ed ca bon (AC). The su ace o he ac i a ed ca bon ha e been modi ied by using sil e nanopa icles. The syn hesis p ocess is simple, cos e ec i e and en i onmen iendly. The modi ied-AC powde s ha e been cha ac e ized by using X- ay di ac ion, scan- ning elec on mic oscopy and su ace a ea and po e size measu emen s. The elec ochemical pe o mance o he p epa ed ma e ials ha e been es ed by ab ica ing symme ic con igu a ion o EDLC by using magnesium-ion based polyme elec oly es. The cells ha e been es ed by using cyclic ol amme y, elec ochemical imped- ance spec oscopy and gal anos a ic cha ge-discha ge echnique. AC wi h 3 w % o sil e p esen s bes esul s wi h speci ic capaci ance o he o de o 398 F g −1 ene gy densi y and powe densi y o 55 Wh kg −1 and 2.4 kW kg −1 making i an in e es ing ma e ial o supe capaci o applica ion. 1. In oduc ion Conside ing he high powe densi y, quick echa ge ime, and long li e, supe capaci o s (SCs) ha e a ac ed a lo o a en ion in ecen yea s [1–4]. They ha e been u ilized in a wide ange o a eas, such as po able and comme cial/household elec onics, g id ins alla ions, and di e en o ms o anspo a ion (buses, ams, olleybuses, e c.) [1–4]. The con igu a ion o a supe capaci o de ice is as simple as con en ional capaci o s [5,6]. An elec oly e (liquid/solid/gel) is sandwiched be- ween wo elec oac i e elec odes o ab ica e a supe capaci o cell [5,6]. On he basis o he ypes o elec ode ma e ials used and he cha ge s o age mechanism, i is classi ied in o wo ypes; (a) elec o- chemical double laye capaci o s (EDLCs) in which la ge su ace a ea ca bonaceous ypes o ma e ials a e used and he cha ge s o age mechanism is elec os a ic in na u e; and (b) pseudocapaci o s, in which conduc ing polyme s and elec oac i e oxides a e used and as a adic cha ge ans e eac ion gi es ise o pseudocapaci ance [1–8]. Ca bon-based ma e ials ha e been applied as a i s ma e ials in elec odes in li hium-ion ba e ies and supe capaci o s due o hei na u al abundance, low cos , high elec ical conduc i i y, and signi i- can capaci ance ela ed o hei high speci ic su ace a ea [9–12]. Di e en o ms o ca bon ha e been es ed as elec ode ma e ials in SCs such as: ca bon nano ubes (CNT), g aphene, ca bon ae ogel, ca bon nano ibe s (CNF) and ac i a ed ca bon (AC) [9–22]. Up o now, ac i- a ed ca bons a e a ac i e elec ode ma e ials o an EDLC capaci o om he economic poin o iew and he possibili y o ob aining a well- de eloped speci ic su ace a ea o ca. 2500 m 2 g −1 wi h a con olled po e size dis ibu ion and also because o i s su ace chemis y which can be easily modi ied o imp o e i s pe o mance by su ace modi ica ion ia; pos ea men o ca bon ma e ials wi h eac i e he e oa om sou ces o by making composi es o ca bon wi h ei he me al oxide ma e ials o conduc ing polyme s [21–25]. Yumak e al. [23] p epa ed he com- posi es o ac i a ed ca bon wi h MnO 2 as well as wi h NiO using hy- d o he mal and p ecipi a ion echniques. The au ho s disco e ed ha adding MnO 2 and NiO o ac i a ed ca bon-based supe capaci o s inc eased hei speci ic capaci ance by 50 % and 150 %, espec i ely [23]. This beha io was asc ibed o he pseudocapaci i e e ec o MnO 2 and NiO, as well as he e ec o oxygen-con aining su ace unc ional g oups de i ed om he composi e syn hesis p ocess [23]. The au ho s also claimed ha he su ace unc ional g oups, su ace a ea, and he - mal s abili y o achie ed composi e ma e ials, as well as he elec o- chemical pa ame e s o ab ica ed supe capaci o s, we e all a ec ed by he syn hesis p ocedu e [23]. Vijayan and co-au ho s [26] p oposed he easy echnique o modi y ac i a ed ca bon ma e ial wi h hin * Co esponding au ho . E-mail add ess: [email p o ec ed] (A. Jain). Con en s lis s a ailable a ScienceDi ec Jou nal o Ene gy S o age jou nal homepage: www.else ie .com/loca e/es h ps://doi.o g/10.1016/j.es .2022.105367 Recei ed 25 Ma ch 2022; Recei ed in e ised o m 20 June 2022; Accep ed 20 July 2022 Jou nal o Ene gy S o age 54 (2022) 105367 2 manganese oxide and hey e ealed ha he bes esul s o a wo- old inc ease in he speci ic capaci ance in 1 M Na 2 SO 4 elec oly e deli - e ed ma e ial o composi ion: 10 w % Mn 2 O 3 @AC [26]. The au ho s es ed hei ma e ial as a symme ic supe capaci o wi h 1 M Na 2 SO 4 elec oly e and he ma e ial had an ene gy densi y o 31 Wh kg −1 , powe densi y o 4.8 kW kg −1 [26]. A edox eac ion was u ilized o deposi he RuO 2 nanopa icles on he mic opo ous ca bon su aces by Y. Zhang and S.-J. Pa k [27]. The ma e ial o composi ion 9 w % RuO 2 @AC had a speci ic capaci ance o 510 Fg −1 , a a cu en densi y o 1 Ag −1 , and he capaci ance e en ion was 87 % a a cu en densi y o 1 Ag −1 a e 3000 cycles [27]. A hin me allic cobal ilm was deposi ed on po ous ca bon (PC) by Vijayan e al. [28]. The modi ied ma e ial (10 w % Co@PC) was examined as an elec ode o aqueous alkaline supe capaci o s in 1 M Na 2 SO 4 and li hium-ion capaci o s using an ionic liquid (1 M LiPF 6 ). The speci ic ene gy and speci ic powe o he aqueous alkaline supe - capaci o buil wi h he Co-modi ied po ous ca bon elec ode we e nea ly 10 imes highe han hose p epa ed wi h he pu e po ous ca bon elec ode [28]. The composi e made o oid-size-ma ched hie a chical 3D i ania lowe s in po ous ca bon (TiO 2 @AC) was syn hesized by he hyd o he mal me hod [29]. The composi e ma e ial was es ed in 1 M Na 2 SO 4 elec oly e and he cons uc ed elec ode in SCs deli e ed 143 F g −1 a 1 A g −1 , ene gy densi y o 28 W h kg −1 , powe densi y o 4.8 kW kg −1 , and he s abili y was 95 % a a cu en densi y o 1 Ag −1 a e 5000 cycles [29]. Hyd o he mal syn hesis was u ilized by Mohamed e al. [30] o ob ain composi e o ZnO@ac i a ed ca bon. The ma e ial was examined as supe capaci o elec ode ma e ial in acidic (H 2 SO 4 ) and alkaline (KOH) elec oly es [30]. The speci ic capaci ance o 667 Fg −1 o ZnO@ac i a ed ca bon composi e showed be e capaci ance pe o mance when compa ed o p is ine AC (355 Fg −1 ) [30]. A e 3000 cycles, he ma e ial main ained 90 % o i s speci ic capaci ance [30]. The goal o as-p esen ed wo ks was o show ha each modi ica ion wi h me allic, me al oxide pa icles, o conduc i e polyme s o o he ca bon ma e ials posi i ely a ec he elec ochemical pe o mances while he ma e ial was es ed as supe capaci o elec ode ma e ial. Mo eo e , he esea che s also claimed ha a e he modi ica ion he achie ed com- posi es ma e ials possessed highe speci ic su ace a ea and po osi y which esul ed o inc ease desi ed pa ame e s o SC applica ions, like speci ic capaci ance, ene gy, and powe densi y. Conside ing he abo e- men ioned ac s in he p esen wo k, he su ace o he ac i a ed ca bon has been modi ied by using sil e (Ag) pa icles, hese pa icles will enhance he elec ical cha ge ans e which inally imp o es he elec- ochemical pe o mance. Kim e al. epo ed he e ec o modi ying he g aphi e nano ibe s and PANI elec ode wi h Ag nanopa icles and ound ha sil e signi ican ly imp o ed he speci ic su ace a ea along wi h he elec ochemical u iliza ion o elec odes [31]. Along wi h he elec ode ma e ials, elec oly es a e also he impo - an componen o ene gy s o age de ice like li hium-ion ba e ies o supe capaci o s [32–35]. Because o hei di e en physical and chem- ical p ope ies, hey play di e en ly a he in e ace wi h di e en elec odes and hence hey possess di e en elec ochemical cha ac e - is ics o he de ice. Though aqueous elec oly es like KOH, H 2 SO 4 , NaCl e c. ha e ad an ages like high ionic conduc i i y, en i onmen ally iendly, cos e ec i e, non- lammabili y e c. bu he main d awback is i s limi ed elec ochemical s abili y ange and unsa e handling [35]. In o de o ind a mid-way, gel polyme elec oly es (GPEs) a e excellen subs i u e due o hei accep able ionic conduc i i y and solid like dimensional s abili y. The mos commonly used polyme s o en ap he liquid elec oly es a e poly( inyl alcohol) (PVA) [36,37], poly( inyl py olidone) (PVP) [38], poly(me hyl me hac yla e) (PMMA) [39], poly ( inylidene luo ide-co-hexa luo op opylene) (PVdF-HFP) [40,41] e c. Ou o hese polyme s, PVdF-HFP is used abundan ly because o i s good mechanical s abili y, he mal s abili y and chemical esis i i y. In he p esen wo k, su ace modi ied ac i a ed ca bon wi h di e en weigh pe cen age o sil e pa icles we e used as an elec ode ma e ial and ee s anding gel polyme elec oly e using PVdF-HFP as hos polyme and magnesium pe chlo a e (Mg(ClO 4 ) 2 ) as sal we e used. Modi ied ac i a ed ca bon has been cha ac e ized by using di e en echniques like BET, XRD and SEM, EDLC cell has been ab ica ed by using su ace modi ied ac i a ed ca bon and GPE. The pe o mance cha ac e is ics o EDLC cells ha e been e alua ed by impedance spec- oscopy, cyclic ol amme y (CV) and gal anos a ic cha ge-discha ge measu emen s. 2. Expe imen al de ails 2.1. P epa a ion o su ace modi ied ac i a ed ca bon The nanocomposi es o ac i a ed ca bon (AC) (Ac i a ed cha coal pu e p.a., CHEMPUR) wi h 1, 3 and 5%w . Ag we e ab ica ed by a acile chemical low- empe a u e ou e. In he i s s ep, AgNO 3 (used as a Ag sou ce, pu chased as a pu e om Lachema) was dissol ed in e hanol solu ion (E OH, 96 %, Me ci) in he weigh a io Ag/AC: 0.01, 0.03, and 0.05, espec i ely. This p ocess was ca ied ou a oom empe a u e. In he second s ep, he AC powde was added o he AgNO 3 -E OH-H 2 O solu ion. The as-p epa ed mix u e was magne ically s i ed o a ew hou s o ob ain a black homogeneously dispe sed suspension. A e - wa ds, he suspension was kep in an ul asonic wa e ba h cleane o 1 h om 25 o 60 ◦C. Each suspension was o e nigh ai -d ied a 60 ◦C and hen a 150 ◦C o a ew hou s. To ob ain a ine powde , he AC/n-Ag (n- deno es: 1, 3 and 5%w . Ag) nanocomposi es we e g inded in an aga e mo a o 1 h. The p epa ed samples om he ea e called as ACAG1, ACAG3, ACAG5. The s uc u e o he p epa ed ca bon ma e ial composi es we e cha ac e ized by using X-Ray powde di ac ion (XRD) by using B uke D8 Disco e Di ac ome e equipped wi h CuK α (λ XRD =1.542 Å) a- dia ion sou ce and by he con ocal Raman spec ome e (Renishaw inVia) equipped wi h a cha ge-coupled de ice (CCD) came a and a con inuous wa e diode pumped Nd:YAG lase wo king a λ =532 nm, espec i ely. Mo phological s udies o ACAG1, ACAG3 and ACAG5 we e ca ied ou by ield emission scanning elec on mic oscopy using he ins umen SEM/FIB-Zeiss C ossbeam 350, Ge many. A he mal analyze DSC SDTQ600, DSC TGA Ins umen was used o s udy he he mal s abili y o ACAG composi e ma e ials om 30 C o 900 C wi h a hea ing a e o 10  C min −1 unde A gon low 20 ml min −1 . The speci ic su ace a eas o he ca bon ma e ials we e measu ed wi h he Au oSo b IQ, Quan ach ome, USA unde ni ogen low. The po e size dis ibu ion cu es we e ob ained by using DFT model. 2.2. Fab ica ion and cha ac e iza ion o EDLC cells GPE ilms we e p epa ed by using s anda d solu ion cas echnique. The de ails o he p epa a ion and cha ac e iza ion o he polyme ic ilms we e desc ibed elsewhe e [42]. The capaci o elec odes we e p epa ed in he o m o lexible elec odes. All he h ee ac i a ed ca bon powde s (ACAG1, ACAG3, ACAG5) we e g inded o 30 min indi idu- ally in pes le mo a o ge a uni o m and ine powde . PVdF is used as a binde in he a io o 90:10 (w/w). PVdF and ace one (sol en ) was magne ically s i ed o 30 min and la e a slu y was pe o med. The slu y was cas ed o e ca bon clo h (A Ca b, USA). The p epa ed elec- odes we e ai d ied a 80 ◦C be o e using hem o ab ica e he EDLC cells. The mass loading o ac i e ma e ial was in be ween 0.39 and 0.43 mg cm −2 . To ab ica e he EDLC cell, GPE we e sandwiched be ween he symme ical elec odes. Th ee EDLC cell (Cell A-C) we e ab ica ed by using ACAG1, ACAG3, ACAG5 espec i ely. All he cells we e elec o- chemically cha ac e ized by using Biologic VMP3 (Seyssine -Pa ise , F ance) elec ochemical wo ks a ion. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 3 3. Resul s and discussion 3.1. S uc u al s udies and mo phology da a (XRD, Raman spec oscopy, SEM, BET and TGA) The XRD pa e n o ac i a ed ca bon (AC) ma e ial, pu e and deco- a ed wi h 1, 3 and 5 % w . Ag is p esen ed in Fig. 1. The AC amo phous peaks a e si ua ed a a ound 26◦and 43◦[12]. The e a e also isible c ys al peaks o pu e AC, coming om g aphi e o o he hexagonal ca bon s uc u es. As shown in Fig. 1, he di ac og ams o ma e ials wi h Ag p esen , ea u e wo cha ac e is ic peaks a 2θ angles o : 38.1, and 44.3◦ o CuK α adia ion (λ =1.542 Å), co esponding o he c ys al planes (111) and (200), espec i ely. Tha wo e lec ions ep esen he me allic Ag phase (COD 9008459). C ys al peak a 32.1 o can be asc ibed o he nanoc ys alline sil e , (122) plane [43]. The peaks in ensi y g ow h wi h he inc ease o Ag con en om 1 o 5 % w . was obse ed and indica ed ha me allic Ag nanopa icles we e success ully deposi ed on he su ace o ac i a ed ca bon ma e ial. These esul s we e u he con i med by SEM analysis as well as ha e ound posi i e e ec while elec ochemical pe o mances we e e alua ed. Acco ding o he Ag single c ys alli es size analysis, hey a e supposed o be below 1 nm, and he Ag pa icles obse ed in SEM, consis ing o many c ys alli es, ha e an a e age size o 10 nm. Raman spec oscopy was u ilized o ge mo e in o ma ion abou he s uc u al ea u es o p is ine AC ma e ial and one selec ed sample o AC modi ied wi h 3%w . Ag. The ob ained esul s a e p esen ed in Fig. 2. The c ys al s uc u e o AC powde s emained unchanged a e Ag modi ica ion, as expec ed. The Raman spec a ea u e ou well-de ined bands a 1340, 1580, 2690, and 2942 cm −1 , which co espond o he D, G, 2D, and D +G bands o ypical g aphi ic ma e ials, espec i ely [12]. A ibu ed o he p e alence o sp 3 hyb idiza ion in he ca bon s uc u e and he E 2g phonon ib a ions o he sp 2 ca bon a oms, he D and G bands a e ela ed wi h he A 1g ib a ional mode o he diso de ed ca bon s uc u e [12,44]. The sca e ing o phonons a he zone bounda y (K poin ) causes he 2D mode, which is a second-o de ib a ion o he G mode [12,43]. The combina ion o D and G peaks can be induced by he p esence o a ious de ec s in he g aphi ic s uc u e [12,44]. I is also possible o es ablish he “deg ee o g aphi iza ion”, which in o ms on he c ys allini y le el o ca bon ma e ials, by compa ing he in ensi y a ios o he D o G bands (I D /I G ) [12,44]. Fo he AC and ACAG3 samples, he es ima ed I D /I G alues a e 1.100 and 1.093, espec i ely. These calcula ions o he in ensi y a ios e ealed ha bo h o he ca bon s uc u es s udied: p is ine AC and AC modi ied wi h 3%w . Ag ma e- ials a e qui e diso de ed. The AC ma e ial modi ied wi h 3%w . Ag has a li le highe deg ee o g aphi iza ion in compa ison o p is ine AC ma e ial. The su ace mic og aphs o sil e modi ied ac i a ed ca bon (ACAG1, ACAG3, ACAG5) a e illus a ed in Fig. 3. As can be seen om he mo phologies ha deposi ion o sil e nanopa icles we e con i med and hey we e obse ed as a small balls (less han 10 nm). Owing o special mo phology which ep esen ac i a ed ca bon ma e ial we could suppose ha he small balls o me allic Ag a e placed be ween he ca - bon nanoshee s. Also, om he mo phology o ACAG3 i can be seen ha he small po es a e de eloped which p o ides he acile accessibili y o elec oly e ions, which a e bene icial in o ming capaci i e in e ace wi h gel polyme elec oly es. The he mal beha io s o ACAG1, ACAG3, and ACAG5 samples we e examined om 30 o 900 ◦C wi h a hea ing a e 10 ◦C min −1 in a gon a mosphe e (Fig. 4). The h ee-s age loss o weigh is obse ed o all analyzed samples. Fi s occu s om he empe a u e 30 o ca. 150 ◦C and is ela ed o he e apo a ion o he esidual wa e (ca. 9 %) as well as accompanies he decomposi ion p ocesses o ca bon ma e ial in o non- condensable gases such as CO, CO 2 , CH 4 , H 2 , and o he s [45]. The weigh loss obse ed in he second s age, be ween ca. 200 ◦C and 600 ◦C, is a ibu able o he hea deg ada ion o aw ma e ials. These eac ions a e accompanied by u he chemical changes such as dehyd a ion, deg ada ion, and condensa ion, all o which esul in he loss o alipha ic cha ac e , inc easing a oma ici y and eleasing gases simul aneously [45]. A he hi d-s age he signi ican e ec o weigh loss o 35 %, 25 %, and 45 % was obse ed in he empe a u e ange om 600 ◦C o 900 ◦C o samples: ACAG1, ACAG3, and ACAG5, espec i ely. Tha s age displays he inal weigh loss, which indica es ha he ac i e si es ha e comple ely eac ed as well as being a measu e o he syn hesized ma e ial's he mal s abili y [45]. N 2 adso p ion-deso p ion iso he ms ha e been eco ded o ACAG1, ACAG3 and ACAG5 powde s and a e ypically shown in Fig. 5(a–c). As can be seen om he iso he ms, all he samples shows an ini ial N 2 up ake ollowed by a g adual inc ease. All iso he ms shows ype II pa e n (IUPAC nomencla u e) in which a e y low p essu es, he mi- c opo es a e ill wi h he ni ogen gas. A he knee, o ma ion o monolaye s a s and mul ilaye o ma ion akes place a he medium p essu e. A he highe p essu es, usually capilla y condensa ion akes place [46]. Table 1 summa izes he alues o a ious pa ame e s es i- ma ed om his s udies. The 45 mic opo e olumes (V mic o ) o all he samples a e es ima ed om -plo me hod and a e abula ed in Table 1. As can be seen om he alues, ACAG3 shows he highes su ace a ea wi h low po e size, bu as he pe cen age o sil e inc eases, i leads o dec ease in mic opo osi y and inc ease o mesopo osi y which leads o dec ease in he speci ic su ace a ea as well. All he ma e ial shows small hys e esis in deso p ion b anch which con i ms he p esence o small amoun o mesopo es along wi h mic opo es. This end is well- Fig. 1. XRD spec a o AC ma e ials modi ied wi h 1, 3 and 5%w . Ag. Fig. 2. Raman spec a o p is ine AC ma e ial and modi ied wi h 3%w . Ag. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 4 connec ed wi h elec ochemical s udies (discussed la e ) as well. The po e size dis ibu ion o each sample is shown in he inse o he espec i e igu es, i has been calcula ed by using Ba e -Joyne - Halenda (BJH) me hod analysis o deso p ion b anch [47–50]. I has been obse ed ha he p epa ed composi ions show he highes con- cen a ion o po es in be ween 0.5 nm o 2.3 nm bu in case o ACAG5, he po e wid h is b oade as compa ed o o he wo composi ions and hence his la ge po es c ea ed was blocked by sil e pa icles. These esul s a e also in synch oniza ion wi h elec ochemical esul s. O e all, we obse ed he ACAG3 has he maximum su ace a ea wi h good and op imized po e size dis ibu ion. 3.2. Elec ochemical s udies Symme ical con igu a ion o he EDLC cells wi h ou ypes o elec ode ma e ials wi h polyme gel elec oly es a e gi en below: Cell#A: ACAG1|GPE|ACAG1 Cell#B: ACAG3|GPE|ACAG3 Cell#C: ACAG5|GPE|ACAG5 Cell#Re : Pu e AC|GPE| Pu e AC As men ioned abo e, ou kind o EDLC cells we e ab ica ed by using su ace modi ied ac i a ed ca bon ma e ials and he esul s has been compa ed wi h p is ine ac i a ed ca bon as well. GPE in he p e- sen s udy is PVdF-HFP-PC-Mg(ClO 4 ) 2 . Compa a i e impedance mea- su emen s, CV and GCD measu emen s ha e been ca ied ou and discussed in his sec ion. Fig. 6a shows he oom empe a u e cyclic ol ammog ams ob ained o cell #A-#C, he CV plo o Cell#Re is shown in supplemen a y ma e ial (Fig. S1). The esul s shows he signi ican con ibu ion o sil e pa icles. A non-symme ic cha ge discha ge p o ile o CV o he elec- ochemical double laye is also e i ied. Ideally he cyclic ol ammo- g ams o he elec ochemical double laye cell is in he o m o symme ical ec angula shape [51]. As can be seen om he cu es ha wi h he inc ease in he pe cen age o sil e , he e is he loss in he symme y and i migh be due o he e e sible pseudo- a adic eac ions and he edox peak becomes p ominen in case o 3 and 5 w % and in he case o pu e and 1 w % o sil e he edox peaks a e almos absen . In e es ingly he e is an inc ease o he elec ic double laye capaci ance in he ol ame ic p o iles om 0 w % o 3 w % and a e ha he e is sha p deg ada ion o he capaci ance alues. I migh be due o he blockage o po es because o he inc eased amoun o sil e pa icles, also BET s udies con i ms ha he su ace a ea o 5 w % o sil e modi ied ma e ial is low and po e size is la ge as compa ed o es o he ma e ials. The end is consis en wi h GCD and impedance s udies also and a e discussed in he ollowing sec ion. Up o 3 w % sil e Fig. 3. SEM images ob ained a 20.000 magni ica ion o : (a) ACAG1, (b) ACAG3, (c) ACAG5 samples. Fig. 4. TGA cu e o ACAG composi es modi ied wi h 1, 3 and 5%w . Ag. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 5 nanopa icles plays a posi i e ole by enhancing he exposed su ace a ea so ha he mos e ec i e elec ochemical double laye p ocess akes place. The CV cu es we e eco ded a he scan a e o 5 mV s −1 in he po en ial ange o 0 V o 1.0 V. The capaci ance alues calcula ed by using CV echnique (Eq. (1)) [49] o cell #A-#C a e 231.5 F g −1 , 362.5 F g −1 and 59.6 F g −1 espec i ely. Cs=∫IdV/s×ΔV×m(1) whe e, s is he scan a e, V is he ol age ange and m is he mass o he ac i e ma e ial used in single elec ode. As can be seen ha he e is a signi ican d op o capaci ance alue o cell #C in which 5 w % Ag is used o su ace modi ica ion. Fig. 6b depic s he a ia ion o capaci ance as a unc ion o scan a e o capaci o cell #A-#C. As can be seen om he plo , a lowe scan a e he e is a sligh dec ease in he alues o capaci ance, a e ha almos Fig. 5. N 2 adso p ion-deso p ion iso he ms and inse ; po e size dis ibu ion spec a o : (a) ACAG1, (b) ACAG3, (c) ACAG5. Table 1 Pa ame e s es ima ed om N 2 adso p ion-deso p ion measu emen s. Sample SSA (BET) m 2 g −1 V mic o (cm 3 g −1 ) D a g (nm) ACAG1 743.2 0.60 0.6 ACAG3 824.7 0.49 0.5 ACAG5 679.9 0.53 0.7 Fig. 6. (a) Compa a i e cyclic ol ame ic cu es o cell #A-#C eco ded a a scan a e o 5 mV s −1 and (b) Va ia ion o speci ic capaci ance o cell #A-#C as a unc ion o scan a e. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 6 s able and cons an capaci ance alues has been obse ed e en o highe scan a es like 100 mV s −1 which shows he as ion swi ching beha io a he in e ace o he elec ode and elec oly e. This con i ms he sui abili y o gel polyme elec oly e o he applica ion o EDLCs. Impedance spec oscopy also called as elec ochemical impedance spec oscopy (EIS) s udies a e ca ied ou o ind insigh in o ma ion abou he capaci o cells such as bulk esis ance, cha ge- ans e esis- ance, di usion phenomenon a he elec ode and elec oly e in e aces and inally he cha ge s o age in e ms o speci ic capaci ance [50]. Fig. 7a shows he impedance (Nyquis ) plo s o he cells #A-#C wi h he magnesium ion based gel polyme elec oly e eco ded in he equency ange om 200 kHz o 1 mHz a oom empe a u e (25 ◦C). The EIS plo o Cell#Re is p o ided in he Supplemen a y ma e ial (Fig. S2) o compa ison. Impedance plo s o any supe capaci o cells a e di ided in o h ee egions, capaci ance a lowe equencies, esis ance a high equencies and ion pene a ion e ec o elec ode ma e ials in he middle equency egion. The e ical line pa allel o he imagina y axis o he impedance plo shows he ideal capaci o beha io . I can be seen om he plo s ha all he cells shows s eep ising in he lowe equency egion which con i ms he capaci i e na u e o all cells. In he high/middle equency ange, he semici cula spu is also obse ed om which he in o ma ion o bulk esis ance, cha ge ans e esis ance a he elec ode elec oly e in e ace can be ob ained. The di e ence in he diame e o he semici cles may be associa ed o he unc ional g oup o he in luence o sil e pa icles on he su ace o ac i a ed ca bon. Simila o CV esul s, impedance esul s also shows he same pa e n, up o 3 w % o sil e pa icles, he alues o capaci ance inc eased and o 5 w % i signi ican ly d opped and he esis ance alue inc eased which clea ly con i ms he blockage o po es o ma e ial when i is modi ied wi h 5 w %. The alues o bulk esis ance R b , cha ge ans e esis ance R c , o e all esis ance R and capaci ance C measu ed a a equency o 1 mHz a e summa ized in Table 2. The capaci ance alues we e calcula ed by using Eq. (2) [49]. C=2 2 π mZ˝ (2) whe e, m is he mass o he single elec ode, is he equency and Z" is he alue o imagina y impedance ypically a 1 mHz. The a e pe o mance o he capaci o cell B has been e alua ed om impedance analysis ollowing he Mille 's app oach [51] by plo ing he Bode plo s o impedances (Z' and Z" s. equency) which a e illus a ed in Fig. 7b. F om hese plo s, he alue o he cha ac e is ic esonan equency ( 0 ) can be ob ained, i is ha in e sec ing poin whe e eal and imagina y alues a e equal. This equency is also known as esponse equency whe e eal and imagina y pa s o impedance has a phase di e ence o ~45◦and he ecip ocal o his equency is called as esponse ime ( τ 0 ). Response ime is basically he ime which is aken by elec oly e ions o adso b and deso b in he po es o he elec ode ma- e ial (ACAG in he p esen case). Fu he , he esponse equency o he Fig. 7. (a) EIS plo s o EDLC cell #A-#C. Expanded ep esen a ion o EIS plo in high/mid equency egion is shown in inse , (b) eal and imagina y impedances e sus equency (c) eal and imagina y capaci ances e sus equency. Table 2 Elec ical pa ame e s o Cell #A-#C om impedance analysis. Cells R c (Ω cm 2 ) R b (Ω cm 2 ) 1 mHz R (Ω cm 2 ) C (mF cm −2 ) a (F g −1 ) b #A 4.2 42.4 600.8 188.7 180 #B 3.1 31.5 124.3 344.3 229.6 #C 5.5 52.5 453.1 112.6 56.3 a O e all capaci ance o cell. b Single elec ode speci ic capaci ance o he cell. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 7 cell B eco ded om Mille Bode plo s has also been es ima ed by using Tabe na plo ( eal and imagina y capaci ance s. equency) and is shown in Fig. 7c. I has been obse ed ha he esponse equencies and hence esponse imes a e in good alignmen wi h he alues ob ained om Mille plo s. The esonan equency o cell B is 0.01 Hz and esponse ime ( τ 0 ) is 14.2 s. The cell has lowe esponse equency and highe esponse ime due o he p esence o sil e ions a he in e ace o he cell. To supplemen he esul s ob ained om EIS and CV, gal anos a ic cha ge-discha ge (GCD) s udies we e also pe o med o e alua e he a e pe o mance o he su ace modi ied ca bon ma e ials. Fig. 8(a) depic s he GCD cu e o cell #A-#C a he cu en densi y o 1.0 mA cm −2 and in a po en ial window o 0 o 1.0 V. All he h ee cells shows he cu ed na u e o cha ge-discha ge pa e ns. The non-linea pa e n in GCD cu es while cha ging and discha ging a e owing o he edox peaks which was obse ed in CV s udies as well. The e e sible edox eac ions a he in e ace because o which pla eau egions appea s du ing cha ge- discha ge a e esponsible o highe alues o capaci ance [52]. The capaci ance was calcula ed using he discha ge b anch excluding he ohmic d op. Fo compa ison GCD cu e o Cell#Re is p o ided as Fig. S3 in supplemen a y in o ma ion. In GCD s udies also, same end has been obse ed capaci ance alues we e g adually inc eased om 0 w % o 3 w % o sil e pa icles and la e i sha ply dec eased in case o 5 w %. The discha ge speci ic capaci ance C d om non-linea discha ge p o ile has been calcula ed by using he Eq. (3) [49]: Cd=4i∫Vd m×V2∣V Vi (3) whe e, i is he cu en densi y, m is he mass o ac i e ma e ial o single elec ode, ∫Vd is he a ea unde he discha ge cu e, V is he maximum ope a ing ol age and V i and V a e he ini ial and inal alues o ol ages on he GCD cu es. Long e m cycling e iciency is ano he s udies by which s abili y o cells a e es ima ed [50]. Con inuous cha ge-discha ge cycles we e ca ied ou o 10,000 cycles a he cu en densi y o 1 mA cm −2 be ween 0 and 1.0 V. The cyclic es ing was pe o med o he bes cell (cell B in he p esen case) and is shown in Fig. 8b. As can be seen om he igu e, he e is a dec ease in ea ly s age o cycling, i may be because o he loss o cha ges esul ing om adso p ion o ions a he elec ode-elec oly e in e ace o accumula ion o ions o o m ion pai s in he cha ge-discha ge cycling p ocess [53]. Ne e heless, he cell B was s able up o 10,000 cycles a e ini ial dec ease in he capaci ance alues. As can be seen om pa e n he capaci ance alues o cell B shows ~2 % o ading in he beginning is possibly because o he i e- e sible s o age componen s o elec oly e and la e i is consis en because o he p ope accessibili y o and non-modi ied po e each- abili y o elec ochemical edox eac ions. The esul s shows he s able cyclic pe o mance o he capaci o cell B. The a ia ion o speci ic discha ge capaci ance o he cell as a unc ion o applied cu en densi y by using GCD echnique is shown in he inse o Fig. 8b. As can be seen om he igu e ha capaci ance g adually inc eased ill 1.4 mA/cm 2 bu la e i s a ed dec easing wi h inc easing cu en densi y which con- i ms he mode a e a e capabili y o he cell. To ge u he insigh , SEM images wi h EDX pa e n o cycled ACAG3 elec odes a e also ca ied ou and a e shown in Fig. 8(c) and EDX pa e n a e shown in inse o Fig. 8c. I can be ha e en a e 10,000 cycles he e is no appa en di e ence be ween he mo phology o be o e cycling samples (Fig. 3b) and a e cycling samples (Fig. 8c) indica ing he s abili y o ACAG samples. Howe e , in he images, we can see some sphe es which may be a e om elec oly e ma e ials, may Fig. 8. (a) GCD cu es o cell #A-#C eco ded a cu en densi y o 1 mA cm −2 in be ween 0 and 1.0 V, (b) Speci ic capaci ance o cell #B e sus cha ge discha ge cycles measu ed a cons an cu en densi y o 1 mA cm −2 (c) SEM image and EDX spec a o ACAG3 elec ode a e cycling. A. Jain e al. Jou nal o Ene gy S o age 54 (2022) 105367 8 be some aces o Mg sal o polyme . F om EDX spec a, i is also clea ed ha he ACAG sample a e cycling con ains aces o Mg, F, O e c. which a e because o he in e ac ion o elec ode and elec oly e ma e ial du ing elec ochemical es ing leading o he dec ease in he numbe o mobile ions wi hin he elec oly e and deme i ing he pe o mance o de ice [53]. To make i mo e clea , he epe i ion o he speci ic capaci ance a e cycling, ac impedance was also ca ied ou a e 10,000 cycles and he plo is shown in supplemen a y Fig. S4. Be o e cycling, he alues o bulk esis ance, cha ge ans e esis ance a e only 31.5 and 3.1 Ω cm 2 espec i ely showing he high conduc i i y and good compa ibili y be- ween elec ode and elec oly e ma e ial bu a e cycling bulk esis- ance is same 31.6 Ω cm 2 bu cha ge ans e esis ance inc eased o 24.4 Ω cm 2 , his con i ms ha decay in he capaci ance s o age is due o cha ge ans e esis ance, elec oly e ions migh s uck in o elec ode leading o dec ease in numbe o ee ions, addi ionally his s uck ions migh also p oduce epulsi e o ce among o he ions hinde ing he ion adso p ion in elec ode elec oly e in e ace and hence inc easing R c [53]. The speci ic ene gy o he cell #A-#C has been calcula ed by using he exp ession E= 1 / 2 CdV2, and he powe densi y o he cells we e calcula ed by using P =E/Δ , whe e Δ is he discha ge ime in he cells [42]. The alues o discha ge capaci ance, ene gy densi y and powe densi y a e summa ized in Table 3. The Ragone plo ( a ia ion o spe- ci ic ene gy E e sus e ec i e powe densi y) o cell B has been e alu- a ed a di e en cu en densi ies; 1.0 mA/cm 2 o 1.8 mA/cm 2 and is shown in Fig. 8(d). The ene gy and powe densi y lies in be ween 3.0 and 5.8 Wh kg −1 and 18.0 o 21.5 kW kg −1 espec i ely. These alues a e ound o be compa able han o he ca bon-based supe capaci o s which a e epo ed in he li e a u e [54–58]. Simila ly like cyclic ol amme y and elec ochemical impedance spec oscopy, GCD also showed he same pa e n, he capaci ance alues, ene gy densi y and powe densi y g adually imp o ed om 0 w % o 3 w % and o 5 w % o sil e pa icles i signi ican ly d opped, i migh be because o he blockage o he po es o he incompa ibili y o po es o elec ode ma e ial wi h e e ence o elec oly e. 4. Conclusions Su ace modi ied ac i a ed ca bon in which he modi ica ion was done by sil e pa icles we e success ully syn hesized and in es iga ed as elec ode ma e ials o elec ochemical double laye capaci o s by using magnesium ion based gel polyme elec oly es. The p ocess o su ace modi ica ion was simple, cheap and sa e as well. The modi ica- ion me hod allowed he deposi ion o me allic sil e in nano-size dimension. The modi ica ion was con i med by SEM, XRD, Raman, and BET analyses. F om he elec ochemical s udies, modi ica ion wi h 3 w % o sil e was op imized o ene gy s o age applica ion. This in e es ing and inimi able a chi ec u e o highly po ous ca bon ma e- ials p o ides a acile and low cos oppo uni y o de eloping elec o- chemical double laye cells. Despi e o low quan i y o sil e deposi ed he e was signi ican inc ease in he p ope ies o he ma e ial. Elec- ochemical s udies o ACAG3 shows excellen esul s ha ing speci ic capaci ance o 398 F g −1 wi h ene gy densi y and powe densi y o 55 Wh kg −1 and 2.4 kW kg −1 . The cell showed he s able pe o mance up o 1500 GCD cycles. Combining all he abo e esul s, ACAG3 can be conside ed as a po en ial candida e o supe capaci o applica ions. CRediT au ho ship con ibu ion s a emen Am i a Jain: Concep ualiza ion, Me hodology, Valida ion, In es i- ga ion, Resou ces, Da a cu a ion, W i ing—o iginal d a p epa a ion, W i ing— e iew and edi ing, Supe ision, P ojec adminis a ion, Funding acquisi ion. Monika Michalska: Me hodology, Valida ion, Fo mal analysis, In es iga ion, W i ing—o iginal d a p epa a ion, W i ing— e iew and edi ing, Visualiza ion, P ojec adminis a ion, Funding acquisi ion. Angelika Zaszczy´ nska: In es iga ion, W i- ing— e iew and edi ing. Pio Denis: W i ing— e iew and edi ing, In es iga ion, Expe imen s. Decla a ion o compe ing in e es The au ho s decla e he ollowing inancial in e es s/pe sonal e- la ionships which may be conside ed as po en ial compe ing in e es s: Am i a Jain epo s inancial suppo was p o ided by Na ional Cen e o Resea ch and De elopmen . Monika Michalska epo s a ela ionship wi h Minis y o Educa ion You h and Spo s o he Czech Republic ha includes: employmen . Da a a ailabili y Da a will be made a ailable on eques . Acknowledgmen s Au ho s a e hank ul o M . M. Milcza ek and D . Kamil Bochenek IPPT PAN o SEM measu emen s. We a e also hank ul o D . Łukasz Rogal, Ins i u e o Me allu gy and Ma e ials Science, Polish Academy o Science, K ak´ ow o TGA measu emen s. 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