Copper-Intercalated Birnessite as a Water Oxidation Catalyst

Abstract

We report a synthetic method to increase the catalytic activity of birnessite toward water oxidation by intercalating copper in the interlayer region of the layered manganese oxide. Intercalation of copper, verified by XRD, XPS, ICP, and Raman spectroscopy, was accomplished by exposing a suspension of birnessite to a Cu(+)-bearing precursor molecule that underwent disproportionation in solution to yield Cu(0) and Cu(2+). Electrocatalytic studies showed that the Cu-modified birnessite exhibited an overpotential for water oxidation of ∼490 mV (at 10 mA/cm(2)) and a Tafel slope of 126 mV/decade compared to ∼700 mV (at 10 mA/cm(2)) and 240 mV/decade, respectively, for birnessite without copper. Impedance spectroscopy results suggested that the charge transfer resistivity of the Cu-modified sample was significantly lower than Cu-free birnessite, suggesting that Cu in the interlayer increased the conductivity of birnessite leading to an enhancement of water oxidation kinetics. Density functional theory calculations show that the intercalation of Cu(0) into a layered MnO2 model structure led to a change of the electronic properties of the material from a semiconductor to a metallic-like structure. This conclusion from computation is in general agreement with the aforementioned impedance spectroscopy results. X-ray photoelectron spectroscopy (XPS) showed that Cu(0) coexisted with Cu(2+) in the prepared Cu-modified birnessite. Control experiments using birnessite that was decorated with only Cu(2+) showed a reduction in water oxidation kinetics, further emphasizing the importance of Cu(0) for the increased activity of birnessite. The introduction of Cu(0) into the birnessite structure also increased the stability of the electrocatalyst. At a working current of 2 mA, the Cu-modified birnessite took ∼3 times longer for the overpotential for water oxdiation to increase by 100 mV compared to when Cu was not present in the birnessite.

Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries

“…The Raman spectra in Fig. 3c also show a match between synthetic birnessite soaked in Cu 2+ and battery-cycled Cu 2+ Bi-δ-MnO 2 , indicating expansion of the birnessite interlayer and pointing the Cu 2+ ions as the origin of the broadening feature365052. This shows that Cu 2+ is intercalated in the Bi-δ-MnO 2 -layered structure during battery cycling, and that this structure is continually reformed upon charging the electrode.…”

“…The resulting composite material benefits from enhanced charge transfer and complete regeneration of layered materials on each cycle. The application of this methodology is not only limited to batteries but also applies to areas where layered materials are of interest like oxidation catalysts36, intercalation chemistry373839 and membranes for removal of heavy-metal ions54.…”

“…As a consequence, the electrode charge transfer characteristics are greatly improved. This holds promise of dramatically improving energy density and energy storage cost and safety, and amplifies recent interest in birnessite for design of catalysts36, lithium (Li) intercalation materials373839 and intercalation of metallic ions into layered structures32. A large-format rechargeable battery with high loadings of Cu 2+ -intercalated Bi-δ-MnO 2 paired with Zn anodes delivering ∼140 Wh l −1 is shown.…”

Nickel Confined in the Interlayer Region of Birnessite: an Active Electrocatalyst for Water Oxidation

“…[8][9][10][11][12][13] Birnessite is an aturally occurring manganese oxide mineral that is ubiquitous in soils,n odules,a nd stream deposits. [8][9][10][11][12][13] Birnessite is an aturally occurring manganese oxide mineral that is ubiquitous in soils,n odules,a nd stream deposits.…”

Enhanced Visible-light Response and Conductivity of the TiO2/reduced graphene oxide/Sb2S3 Heterojunction for Photoelectrochemical Water Oxidation

“…S1(f) in the ESI. The low frequency for a Nyquist plot is useful for the information about the charge-transfer resistance at the interface between the electrolyte and the catalytic surface, i.e., the TiO 2 /rGO surface for this case, while the high frequency region is applied to estimate the charge-transfer resistance between the catalytic surface and reactants, i.e., the TiO 2 /rGO surface and the aqueous solution [6,21]. The charge-transfer resistance (R ct ) at the interface between the TiO 2 /rGO surface and the aqueous solution can be estimated by observing the semicircle at the high frequency region.…”