Probing metal-organic frameworks during water oxidation electrocatalysis

Zhao et al. employed operando X-ray absorption spectroscopy to examine the structural change of Ni0.5Co0.5-MOF-74 during electrochemical water oxidation. Ni and Co metal nodes undergo a simultaneous transition from hydroxide oxyhydroxide analogs as higher anodic potentials are applied. Discovery more effective oxygen evolution reaction (OER) catalysts is critical for achieiving high rate energy efficient electrolyzers.1Hu C. Zhang L. Gong J. Recent progress made in mechanism comprehension design electrocatalysts alkaline splitting.Energy Environ. Sci. 2019; 12: 2620-2645Crossref Google Scholar More recently, that have been investigated OER drawn attention their ability not only produce molecular but also participate oxygen-atom transfer reactions.2Jin K. Maalouf J.H. Lazouski N. Corbin Yang D. Manthiram Epoxidation Cyclooctene Using Water Oxygen Atom Source at Manganese Oxide Electrocatalysts.J. Am. Chem. Soc. 141: 6413-6418Crossref PubMed Scopus (45) Scholar,3Maalouf Jin Limaye A.M. Kinetic Analysis Electrochemical Lactonization Ketones Source.ACS Catal. 2020; 10: 5750-5756Crossref (9) The versatility these makes in-depth understanding structure-activity relationships catalytic mechanisms even important. desire commercial implementation has motivated research efforts develop non-precious metals; first row oxides electrolytes reported promising electrocatalysts. It shown oxyhydroxides evolve on surfaces many types oxide However, origin activity picture surface under polarization still active investigation.4Burke M.S. Enman L.J. Batchellor A.S. Zou S. Boettcher S.W. Evolution Reaction Electrocatalysis Transition Metal Oxides (Oxy)hydroxides: Activity Trends Design Principles.Chem. Mater. 2015; 27: 7549-7558Crossref (740) (XAS) powerful technique probe local structure sites. scattering events ejected electrons affected by neighboring atoms, giving information number distance neighbors central atom. As exact catalyst operating conditions can be significantly different its pristine form, XAS experiments warranted understand accurately.5Li X. Huang Y. Liu B. In Situ/Operando Techniques Characterization Single-Atom Catalysts.ACS 9: 2521-2531Crossref (155) Challenges studying heterogeneous often arise crowded, coupled, inconsistent Molecular tuning moieties varying steric electronic properties restricted packed sites, limited control hampers mechanistic catalysts. When bulk-sensitive spectroscopic techniques like applied typical catalysts, identifying signals specific sites difficult. On other hand, crystalline porous materials such zeolites metal-organic frameworks (MOFs) excellent platforms studies; periodic atomic-scale building units MOFs provide concentration dispersed sites.6Chen Xu Q. Metal-Organic Framework Composites Catalysis.Matter. 1: 57-89Abstract Full Text PDF (152) recent work, report transformation bimetallic MOF-74 oxidation.7Zhao Tan He C.T. An P. Xie F. Jiang Zhu Wu K.H. Li H. al.Structural highly metal–organic framework reaction.Nat. Energy. 5: 881-890Crossref (262) Operando analysis provided profound insights into species. authors evaluated toward with rotating disk electrode setup 1 M KOH solution. overpotential less than 270 mV current density 10 mA cm−2, turnover frequency 0.86 s−1, Tafel slope 49 dec−1, ∼100% Faradaic efficiency comparable catalysts.4Burke characterization demonstrates distinct phases nanocrystals an average size 80 nm deposited carbon paper (Figure 1A). presence isosbestic points near-edge (XANES) spectra 1.1 V 1.5 versus reversible hydrogen (RHE) suggests represent mixtures two constituents. bimodal peak appeared 1.3 resembles combination peaks V, which agrees consecutive ranging comparison standard samples indicates K-edge species appearing lower analogous β-Ni(OH)2, whereas those similar γ-NiOOH. agree well β-Co(OH)2 γ-CoOOH analogs, respectively. conclude changes involve forming analog resting state state. as-formed oxyhydride do immediately reverse back backward scan, slowly recovers after being exposed air 15 days. This MOF undergoes microstructural polarization, does degrade. Fourier-transformed extended fine (EXAFS) show decreased M-O, M-M, M-M-M distances increasing potentials. shrinkage interatomic constructs denser edge-sharing packing upon applying potential. Importantly, rule out possibility destructive aggregation micro fluorescence images shows uniform distribution both elements potential range interest. study presented this work successfully how responds short timescales; future studies may through durability long-term electrolysis. revealed among NiCo-MOF-74 various ratios, highest activity, it coincides synchronous 1B). nonlinear transitions sharp decrease Ni/Co–O Ni/Co–M bond lengths coordination shifts No apparent evident up RHE when component, suggesting reconstruction centers driven components system. were able apply relationship NiFe-MOF-74 optimal Fe ratio was experimentally determined, Ni0.9Fe0.1-MOF showed best performance, exhibiting 198 cm−2. sequentially transforms potential, concurrent observed. Electronic calculation ratios metals one way activities. O 2p-band level relative Fermi activity-related parameter perovskite oxides.8Wu T. Sun Song Xi Du Chen Sasangka W.A. Liao Gan C.L. Scherer G.G. al.Iron-facilitated dynamic active-site generation spinel CoAl2O4 self-termination oxidation.Nat. 2: 763-772Crossref (352) would interesting see if level. Investigating conductivity mixed-metal interest because could contribute enhanced activity.9Trotochaud Young S.L. Ranney J.K. Nickel-iron oxygen-evolution electrocatalysts: role intentional incidental iron incorporation.J. 2014; 136: 6744-6753Crossref (2023) superior compared monometallic counterparts provides molecular-level synergetic effects present composed multiple further exploration desirable. Developing systems well-defined tunable will allow deconvoluted improve our relationships. future, useful predict composition before screening combinations, based gained study. For example, learning Ni0.9Fe0.1-MOF-74 cases, what give transformation, order find another working set without extensive screening. should noted organic ligands interaction affect structures stability catalysts.10Wang Shen Arandiyan Garbrecht M. Su Z. Han Tricoli A. al.Engineering Stability MOF-Nanocomposites Efficient Oxidation.Adv. Energy 2021; 11: 2003759Crossref (32) result probing operation. endeavors implement situ measurements realistic using diverse better wider