Electroactive materials based on pyrazine and quinone units

Trenutno uporabljani akumulatorji v električnih avtomobilih vsebujejo anorganske katodne materiale na osnovi kovin prehoda. Kot alternativo anorganskim katodnim materialom se v zadnjih letih izpostavlja organske katodne materiale, katerih prednost predstavljajo nižja cena, višja teoretična kapaciteta, večja okoljska sprejemljivost in možnost uporabe virov iz biomase. Sintetizirali smo več organskih katodnih materialov na osnovi pirazinskih in kinonskih enot ter njihovo delovanje preizkusili z galvanostatskimi meritvami v modelnem litijevem akumulatorju, del smo jih preizkusili tudi v modelnem magnezijevem akumulatorju. Sintetizirani 5,14-dihidro-5,7,12,14-tetraazapentacen (DHTAP) na osnovi pirazinskih enot je v prvih ciklih v modelnem litijevem akumulatorju dosegel specifično kapaciteto 180 mAhg-1, ki je blizu teoretični. V strukturo smo z oksidacijo »dodali« kinonske enote, s čimer je 5,7,12,14-tetraaza-6,13-pentacenkinon (TAPK) v modelnem litijevem akumulatorju v prvi praznitvi dosegel specifično kapaciteto 324 mAhg-1 pri višji napetosti kot DHTAP. Pri obeh sintetiziranih spojinah smo med galvanostatskimi meritvami opazili postopno upadanje specifične kapacitete zaradi odtapljanja aktivnega materiala v elektrolit. Problem topnosti katodnega materiala v elektrolitu smo reševali z vključitvijo osnovne strukturne enote DHTAP v povečan zvezdast analog, kjer smo za sintezo uporabili heksaketocikloheksan oktahidrat, derivat mio-inozitola, ki ga je možno pridobiti iz biomase. S tem smo povečali stabilnost delovanja in hkrati povečali tudi specifično kapaciteto, ki je dosegla 230 mAhg-1 in se v 100 ciklih ni bistveno spremenila. Zvezdastemu analogu smo z oksidacijo, analogno kot pri manjšem TAPK, v strukturo »dodali« kinonske enote. Učinek je bil slabši od pričakovanega, saj je s K2Cr2O7 oksidiran produkt v prvi praznitvi dosegel 173 mAhg-1, kar je skoraj polovico manj od TAPK, hkrati pa je bil material kljub večji velikosti molekule topen v elektrolitu, kar je privedlo do postopnega upadanja specifične kapacitete. Z reakcijo med 2,3-diaminofenazinom in 2,5-dihidroksi-1,4-benzokinonom smo poskušali sintetizirati povečan dimerni analog DHTAP. Z MALDI-TOF masno spektrometrijo smo ugotovili, da sinteza ni bila uspešna, produkt pa najverjetneje vsebuje oligomere 2,3-diaminofenazina. Produkt smo preizkusili v modelnem litijevem akumulatorju, kjer je dosegel stabilno kapaciteto, ki je po 100 ciklih znašala 187 mAhg-1. Najpogosteje uporabljeni pristop za zmanjšanje topnosti katodnega materiala v elektrolitu predstavlja oligomerizacija/polimerizacija osnovne strukturne enotev ta namen smo s kondenzacijsko reakcijo med heksaketocikloheksan oktahidratom in tetraamino-p-benzokinonom poskušali v polimer/oligomer hkrati vključiti kinonsko in pirazinsko strukturo. Sintetizirani material je v modelnem litijevem akumulatorju dosegel slabšo specifično kapaciteto od pričakovane, okoli 120 mAhg-1, a z boljšo stabilnostjo, saj nismo opazili odtapljanja aktivnega materiala v elektrolit.Currently used batteries in electric vehicles have cathodes consisting of inorganic materials based on transition metals. Recently an alternative to inorganic cathodes has emerged in the form of organic cathode materials, which benefit from lower costs, higher theoretical capacities, lower environmental impact and the option to use biomass derivates. We synthesized several organic cathode materials based on quinone and pyrazine units and tested them with galvanostatic measurements in a model lithium battery, some of them were also tested in a model magnesium battery. Synthesized 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) based on pyrazine units delivered a specific capacity of 180 mAhg-1 in the first cycles, which is close to its theoretical capacity. With oxidation of DHTAP quinone units have been »added« into the structure, which increased the potential and specific capacity of 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ) reaching 324 mAhg-1 in the first discharge of a model lithium battery. Both synthesized materials showed gradual capacity fading due to the dissolution of the active material in the electrolyte. We tried to solve this problem and improve the battery characteristics by incorporating the basic structural unit of DHTAP into a bigger star shaped molecule using a hexaketocyclohexane octahydrate, a derivate of myo-inositol, a compound obtained from waste biomass. Synthesized material showed improved cycling stability delivering a specific capacity of 230 mAhg-1, which remained constant throughout 100 cycles. We employed the same strategy of incorporating quinone units into the star shaped DHTAP analogue through the oxidation process. The oxidation of the material did not bring expected results, as the oxidized material reached specific capacity of 173 mAhg-1 in its first discharge, which is only a half of the capacity of TAPQ. The oxidized material was also soluble in the electrolyte, which was the reason for the observed fast specific capacity fading. We tried to employ a reaction between 2,3-diaminophenazine and 2,5-dihydroxy-1,4-benzoquinone to synthesize a bigger DHTAP analogue. The analysis with MALDI-TOF mass spectrometry showed, that the synthesis did not deliver the expected product, which is probably comprised of the oligomers of 2,3-diaminophenazine. We tested the obtained product in a model lithium battery in which it delivered a specific capacity of 187 mAhg-1 in the 100th cycle with slow capacity fading. Most commonly used strategy to prevent the dissolution of the active material in the electrolyte is the incorporation of the basic structural unit into an oligomer/polymer. In order to employ this strategy, we used a condensation reaction between hexaketocyclohexane octahydrate and tetraamino-p-benzoquinone. Obtained product delivered a lower than expected specific capacity of 120 mAhg-1 in a model lithium battery, without the dissolution of the active material in the electrolyte

Design of organic cathode material based on quinone and pyrazine motifs for rechargeable lithium and zinc batteries

Despite the rapid expansion of the organic cathode materials field, there is still a lack of materials obtained through facile synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAhg-1 with an average voltage of 2.63 V vs. Li/Li+ in the Li-ion battery. That corresponds to an energy density of 860 Whkg-1 on the material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82 % after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in Zn-organic battery using aqueous electrolyte, reaching the specific capacity of 326 mAhg-1 with an average voltage of 0.86 V vs. Zn/Zn2+. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading

Design of organic cathode material based on quinone and pyrazine motifs for rechargeable lithium and zinc batteries

Despite the rapid expansion of the organic cathode materials field, we still face a shortage of materials obtained through simple synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of a small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox-active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAh g$^{−1}$ with an average voltage of 2.63 V vs Li/Li$^+$ in the Li-ion battery. That corresponds to an energy density of 860 Wh kg$^{−1}$ on the OTQC material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82% after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in aqueous Zn−organic battery, reaching the specific capacity of 326 mAh g$^{−1}$ with an average voltage of 0.86 V vs Zn/Zn$^{2+}$. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading

Synthesis of organic cathode materials with pyrazine and catechol motifs for rechargeable lithium and zinc batteries

Although there are many reports on novel small organic cathode materials for rechargeable lithium and zinc batteries, there is still a lack of materials obtained with a facile synthesis from commercially available precursors, which also exhibit satisfactory cycling stability. Herein, we report a simple synthetic procedure for the simultaneous introduction of carbonyl and pyrazine units into small organic cathode materials. Materials were prepared through a condensation reaction between aromatic diamines and the sodium salt of rhodizonic acid. Building on an already known oxidized diquinoxalinecatechol (ODQC) material with cycling stability issues stemming from the dissolution in the electrolyte, we designed an expanded conjugated structure tetraquinoxalinecatechol (TQC). The ODQC shows fast capacity fading in Li-organic batteries having capacity retention of 16.8 % after 300 cycles at a current density of 50 mAg-1. The synthesis of the bigger TQC analog with lower solubility improves cycling stability with a high capacity retention of 82 % after 300 cycles at a current density of 50 mAg-1 and a maximum specific capacity of 223 mAhg-1 at an average voltage of 2.42 V vs. Li/Li+. In Zn-organic battery employing an aqueous electrolyte, TQC delivers a high maximum specific capacity of 301 mAhg-1 at 50 mAg-1 with an average voltage of 0.76 V, and 71 % capacity retention after 100 cycles

High-surface-area organic matrix tris(aza)pentacene supported platinum nanostructures as selective electrocatalyst for hydrogen oxidation/evolution reaction and suppressive for oxygen reduction reaction

Developing a Pt-based electrocatalytic material able to selectively catalyze hydrogen oxidation (HOR) while supressing oxygen reduction (ORR) is beneficial for durability of the fuel cells. Namely, degradation of carbon supported Pt particles is dramatically influenced by the unwanted ORR enrolling at the anode due to the air penetration during start-up/shut-down events. We present an organic matrix tris(aza)pentacene (TAP), which belongs to π-functional materials with ladder-like conjugated nitrogen-containing units, as the support for Pt to form a “smart” fuel cell anode able to selectively catalyze HOR and to suppress ORR. “Switching-on/off” of the composite material activity is provided by reversible reduction/oxidation of the TAP in the low potential region which provokes TAP - HxTAP transition. Conductivity of the reduced HxTAP enables supported Pt particles to effectively run HOR. In contrast, restricted conductivity of oxidized TAP analogue leads to the substantial drop in the ORR activity with respect to benchmark Pt/C catalyst

Suppressing platinum electrocatalyst degradation via a high-surface-area organic matrix support

Degradation of carbon-supported Pt nanocatalysts in fuel cells and electrolyzers hinders widespread commercialization of these green technologies. Transition between oxidized and reduced states of Pt during fast potential spikes triggers significant Pt dissolution. Therefore, designing Pt-based catalysts able to withstand such conditions is of critical importance. We report here on a strategy to suppress Pt dissolution by using an organic matrix tris(aza)pentacene (TAP) as an alternative support material for Pt. The major benefit of TAP is its potential-dependent conductivity in aqueous media, which was directly evidenced by electrochemical impedance spectroscopy. At potentials below ∼0.45 V$_{RHE}$, TAP is protonated and its conductivity is improved, which enables supported Pt to run hydrogen reactions. At potentials corresponding to Pt oxidation/reduction (>∼0.45 V$_{RHE}$), TAP is deprotonated and its conductivity is restricted. Tunable conductivity of TAP enhanced the durability of the Pt/TAP with respect to Pt/C when these two materials were subjected to the same degradation protocol (0.1 M HClO$_4$ electrolyte, 3000 voltammetric scans, 1 V/s, 0.05−1.4 V$_{RHE}$). The exceptional stability of Pt/TAP composite on a nanoscale level was confirmed by identical location TEM imaging before and after the used degradation protocol. Suppression of transient Pt dissolution from Pt/TAP with respect to the Pt/C benchmark was directly measured in a setup consisting of an electrochemical flow cell connected to inductively coupled plasma-mass spectrometry