Atomic tuning on cobalt enables aneightfold increase of hydrogen peroxideproduction13 January 2020

3D image of single cobalt atoms on nitrogen-dopedgraphene. It was crucial for this study to control thecoordination environment of single cobalt atom, sincethis coordination structure directly affects the catalyticproperties of the overall catalyst. Credit: IBS

IBS scientists and their colleagues have recentlyreport an ultimate electrocatalyst that addresses allof the issues that trouble H2O2 production. Thisnew catalyst comprising the optimal Co-N4

molecules incorporated in nitrogen-doped

graphene, Co1-NG(O), exhibits a record-highelectrocatalytic reactivity, producing up to 8 timeshigher than the amount of H2O2 that can begenerated from rather expensive noble metal-based electrocatalysts.

Just as we take a shower to wash away dirt andother particles, semiconductors also require acleaning process. However, its cleaning goes toextremes to ensure even trace contaminants "leaveno trace." After all the chip fabrication materials areapplied to a silicon wafer, a strict cleaning processis taken to remove residual particles. If this high-purity cleaning and particle-removal step goeswrong, electrical connections in the chip are likelyto suffer from it. With ever-miniaturized gadgets onthe market, the purity standards of the electronicsindustry reach a level equivalent to finding a needlein a desert.

That explains why hydrogen peroxide (H2O2), amajor electronic cleaning chemical, is one of themost valuable chemical feedstocks that underpinsthe chip-making industry. Despite the ever-growingimportance of H2O2, its industry has been left withan energy-intensive and multi-step method knownas the anthraquinone process. This is anenvironmentally unfriendly process which involvesthe hydrogenation step using expensive palladiumcatalysts. Alternatively, H2O2 can be synthesizeddirectly from H2 and O2 gas, although the reactivityis still very poor and it requires high pressure.Another eco-friendly method is to electrochemicallyreduce oxygen to H2O2 a via 2-electron pathway.Recently, noble metal-based electrocatalysts (forexample, Au-Pd, Pt-Hg, and Pd-Hg) have beendemonstrated to show H2O2 productivity althoughsuch expensive investments have seen low returnsthat fail to meet the scalable industry needs.

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Atomic-level tuning of Co-N4/graphene catalyst. Cobaltatoms are coordinated with four nitrogen atoms formingsquare planar Co-N4 structure on nitrogen-dopedgraphene (Co-N4/graphene). Researchers could controlthe charge state of cobalt atoms by introducing electron-rich (for example, oxygen) or electron-poor (for example,hydrogen) atoms near the Co-N4 structure. Specifically,when electron-rich oxygen atoms were near Co-N4 (Co-N4(O)), the charge state of cobalt atoms slightlydecreased becoming electron-poor cobalt whichexhibited significant enhancement on electrochemicalH2O2 production. Conversely, when electron-richhydrogen atoms were near the Co-N4 structure, Co-N4(2H), cobalt atom became electron-rich making it lessfavorable for H2O2 production. Credit: IBS

Researchers at the Center for NanoparticleResearch (led by Director Taeghwan Hyeon andVice Director Yung-Eun Sung) within the Institutefor Basic Science (IBS) in collaboration withProfessor Jong Suk Yoo at the University of Seoulrecently report an ultimate electrocatalyst thataddresses all of the issues that hinder H2O2

production. This new catalyst comprising theoptimal Co-N4 molecules incorporated in nitrogen-doped graphene, Co1-NG(O), exhibits a record-highelectrocatalytic reactivity, producing up to 8 timesmore H2O2 than can be generated from relativelyexpensive noble metal-based electrocatalysts (forexample, Pt, Au-Pd, Pt-Hg and so on). Thesynthesized catalysts are made from element at

least 2000 times less expensive (Co, N, C, and O)than the conventional palladium catalyst, and theyare exceptionally stable without activity loss over110 hours of H2O2 production.

Typically involving different phases of catalysts(usually solid) and reactants (gas), heterogeneouscatalysts are widely exploited in many importantindustrial processes. Still, their catalytic propertywas thought to be controlled only by changing theconstituent elements. In this study, the researchersverified that they can induce a specific interactionon heterogeneous catalysts by fine-tuning the localatomic configurations of the elements as seen inenzyme catalysts (Fig.2). Director Hyeon, thecorresponding author of the study notes, "this studysuccessfully demonstrated the possibility ofcontrolling a catalytic property by tuning atomiccompositions. This finding may bring us closer todiscovering the fundamental properties of catalyticactivities."

Based on theoretical analysis, it was verified thatthe charge density of a cobalt atom on nitrogen-doped graphene is highly dependent on thecoordination structure surrounding the cobalt atom.Therefore, the researchers could control electrondensity of cobalt atoms by introducing eitherelectron-rich or electron-poor species such asoxygen or hydrogen atoms. When electron-richoxygen atoms are nearby, Co atoms becomeelectron-deficient. On the other hand, when anelectron-rich hydrogen atom is nearby, the oppositetrend was found (which would generate electron-rich Co atoms). Very interestingly, the electrondensity of Co atoms were critical for theelectrochemical H2O2 production.

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Summary of H2O2 productivity for variouselectrocatalysts. 1 kg of optimized Co1-NG(O) catalystcan produce 341.2 kg of H2O2 within 1 day, which is upto 8 times higher the amount of H2O2 that can beproduced by the state-of-the-art noble metalelectrocatalysts. Credit: IBS

Next, the researchers designed the optimal cobaltatomic structure (Co1-N4(O)) by having all of therequired conditions such as precise selection ofelement, synthesis temperature and variousexperimental conditions met. Combining theoreticalsimulations and nanomaterial synthesistechnologies, the researchers were able to controlthe catalytic property in atomic precision. Withelectron-poor Co atoms (Co1-NG(O)), they wereable to produce H2O2 with significantly high activityand stability, far surpassing the state-of-the-artnoble metal catalysts. Conversely, electron-rich Coatoms exhibited a high reactivity for 4-electronoxygen reduction reaction to H2O formation whichmight be found useful for fuel cell applications.

Surprisingly, 341.2 kg of H2O2 can be producedwithin 1 day at room temperature and atmosphericpressure using 1 kg of Co1-NG(O) catalyst. Thisamount of H2O2 is up to 8 times higher the amountof H2O2 produced by the state-of-the-art noblemetal catalysts (Fig.3). Co1-N4(O)) is a catalyst thatallows low-cost, efficient, and eco-friendlyproduction of H2O2.

Professor Sung, the corresponding author says,"For the first time, we found that the catalytic

property of heterogeneous catalysts can be fine-tuned with atomic precision. This unprecedentedresult will help us to understand previous unknownaspects of electrochemical H2O2 production. Withthis knowledge, we could design a scalable catalystthat is entirely composed of earth-abundantelements (Co, N, C, and O)."

The study is published in Nature Materials.

More information: Atomic-level tuning of Co–N–Ccatalyst for high-performance electrochemical H2O2

production, Nature Materials (2020). DOI:10.1038/s41563-019-0571-5 , nature.com/articles/s41563-019-0571-5

Provided by Institute for Basic Science

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APA citation: Atomic tuning on cobalt enables an eightfold increase of hydrogen peroxide production(2020, January 13) retrieved 30 September 2021 from https://phys.org/news/2020-01-atomic-tuning-cobalt-enables-eightfold.html

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