Synergistic effects in oxygen evolution activity of mixed iridium-ruthenium pyrochlores

Pyrochlore oxides (A2B2O7 ) simultaneously containing iridium and ruthenium in the B-site are promising catalysts for oxygen evolution reaction (OER) in acid media. The catalytic activity of the pyrochlore based catalysts is increased by the coexistence of Ir and Ru in the B-site of the pyrochlore structure. Lanthanide (Yb, Gd, or Nd) stabilized mixed pyrochlores with a fraction of Ru in the B-site of x Ru = 0.2, 0.4, 0.6, 0.8 were synthesized by the spray-freeze freeze-dry approach. All prepared mixed pyrochlore catalysts are surpassing the OER activity of the corresponding iridium and ruthenium analogues featuring no cation mixing as well as that of the benchmark IrO2 catalyst. The synergy of Ir and Ru in the B-site of the pyrochlore structure suppresses the effect of the A-site cation radius on the OER activity. The observed OER activity scales with the Ir-Ru bond distance which represents the local structure of the prepared materials. The most active ytterbium catalyst also shows a significant stability improvement under OER operando conditions over the benchmark IrO

Synergetic Surface Sensitivity of Photoelectrochemical Water Oxidation on TiO2 (Anatase) Electrodes

Tato práce porovnává fotoelektrokatalytickou aktivitu a selektivitu nanokrystalické anatasy, v níž převládají tváře {110}, {101} a {001} v fotoelektrickém katalytickém dělení vody. Ačkoli anodická polovina reakce rozštěpení vody - vývoji oxygenu vede k celkovému fotoelektrochemickému chování fotoexcitované anatázy, současná redukce v podmínkách fotoelektrochemie je také pozorována na některých anatasových plochách. Aktivita jednotlivých aspektů anodické poločinné reakce štěpení vody (vývoj kyslíku) se zvyšuje v pořadí {101} <{110} <{001}. Zvyšující se oxidační aktivita sleduje tendenci povrchu vytvářet meziprodukty produkující radikál OH (H2O2, ozón) v stavech zachycených otvorů. Aktivity v redukčních procesech se zvyšují v obráceném pořadí. Konkrétně redukční aktivita {101} orientované anatázy může být přičítána výraznému vývoji vodíku přenosem fotogenerovaných elektronů nábojem. Pozorované trendy souhlasí s modely DFT, které potvrzují možnost racionálního návrhu fotokatalyzátorů.The paper compares photoelectrocatalytic activity and selectivity of nanocrystalline anatase dominated by {110}, {101}, and {001} faces in photo(electro)catalytic water splitting. Although the anodic half-reaction of water splittingoxygen evolutiondominates the overall photoelectrochemical behavior of the photoexcited anatase, simultaneous reduction under photoelectrochemical conditions is also observed on some anatase faces. The activity of individual facets in anodic half-reaction of water splitting (oxygen evolution) increases in the order {101} < {110} < {001}. The increasing oxidation activity tracks the tendency of the surface to generate the OH• radical producing intermediates (H2O2, ozone) on the trapped hole states. The activity in reduction processes increases in the reversed order. Particularly, the reduction activity of the {101} oriented anatase can be attributed to pronounced hydrogen evolution by a charge transfer of photogenerated electrons. The observed trends agree with DFT-based models which confirm the possibility of a rational design of the photocatalysts

Synergistic effect of p-type and n-type dopants in semiconductors for efficient electrocatalytic water splitting

Co-substituting a stable material, e.g. TiO2, with both n- and p-type dopants, allows tuning its reactivity to activate the material for oxygen evolution. This opens up a new design avenue for acid water electrolysis electrocatalysts