Discovery and Characterization of a Pourbaix Stable, 1.8 ev Direct Gap Bismuth Manganate Photoanode

Transcription

1 Supplementary Information for Discovery and Characterization of a Pourbaix Stable, 1.8 ev Direct Gap Bismuth Manganate Photoanode Paul F. Newhouse, Sebastian E. Reyes-Lillo, Guo Li, Lan Zhou, Aniketa Shinde, Dan Guevarra, Santosh K. Suram, Edwin Soedarmadji, Matthias H. Richter, Xiaohui Qu, Kristin Persson, Jeffrey B. Neaton*, and John M. Gregoire* Photoelectrochemistry data on inkjet-printed material a. b.

2 c. Figure S1. 44 second (back-side) chopped-illumination chronamperometry measurements in FCN13 for the Bi40Mn60Ox and Bi30Mn60Sm10Ox samples from Figure 1 using (a) 385 nm and (b) 455 nm LED illumination (irradiance = and mw/cm 2, respectively). (c) Backside, chopped-illumination OER13 photocurrent measurements from duplicate sample compositions as those from Figure 1 using 455 nm illumination. See table S3 below for a list of pertinent illumination parameters. Figure S2. One of 2 illumination cycles of (front-side) chopped-illumination chronoamperometry using LED wavelengths from 387 to 603 nm (Doric LEDC4-385/Y/G/A_SMA with 387, 451, 515, 603 nm; irradiance = 585.2, 378.7, 167.0, mw/cm 2, respectively) for sample Bi40Mn60Ox in a 0.1 M NaOH electrolyte with 0.25 M sodium sulfate and 0.01 M sodium sulfite as a hole acceptor. The photocurrent is calculated as the difference between the steady state illuminated current (averaged over the latter half of the illumination period) and the average of the steady state pre- and post- dark currents.

3 Synchrotron XRD data on inkjet-printed materials Figure S3. An as-synthesized synchrotron XRD image from the Bi40Mn60Ox sample from Figs. 1 and 2. The smoothly-varying diffraction rings indicate an equi-axed, powder-like crystallite distribution within the thin film sample.

4 Analysis of PVD library a. b. c. Figure S4. (a) Example of one XRD signal from phase-pure BiMn2O5 in the sputter-deposited library. (b) The XRD images from which the signal was obtained with smoothly-varying diffraction rings indicating an equi-axed, powder-like crystallite distribution within the thin film. (c) Short circuit photocurrent density based on 44 s chronoamperometry measurements in FCN13 with 0.5 s on/off, back-side toggled-illumination (385 nm), as a function of Mn concentration (obtained by XRF measurements). The maximum photocurrent density appears within the phase pure BiMn2O5 region. As composition increase or decreases from the phasepure region, the photocurrent density drops rapidly, presumably due to deleterious effects of mixing BiMn2O5 with other phases.

5 Additional Pourbaix Diagrams Figure S5. Comparison of calculated Pourbaix diagrams for α-fe2o3 and BiMn2O5.

6 Figure S6. Pourbaix diagrams for Bi and Mn, respectively, showing that the region of stability for BiMn2O5 surpasses the union of the stability regions for MnO2 and Bi4O7.

7 Details of calculations with 4 magnetic configurations Experimentally, BiMn2O5 display a paramagnetic room temperature phase and a multiferroic ground state at low temperatures. The room temperature orthorhombic Pbam symmetry requires that both groups of Mn environments, i.e. octahedral and squared pyramidal oxygen motifs, have the same spin configuration. At low temperatures, inversion symmetry is broken due to the coupling between charge ordering and magnetic exchange and leads to a polar ground state structure with orthorhombic space group Pmc21. Among all the spin configuration considered in this work, we expect that AFM-2 correspond to the best representation of the multiferroic ground state. Figure S7. HSE band diagrams of BiMn2O5 with noted magnetic configurations. The energy is set to zero at the valence band maximum. The symmetry points in the Brillouin zone correspond to Γ=(0,0,0), X=(1/2,0,0), S=(1/2,1/2,0), Y=(0,1/2,0), Z=(0,0,1/2), U=(1/2,0,1/2), R=(1/2,1/2,1/2) and T=(0,1/2,1/2).

8 Figure S8. HSE pdos of BiMn2O5 with noted magnetic configurations. The energy is set to 0 at the valence band maximum. Table S1. Total energies (mev/f.u.) and lattice parameters (Å) computed for the different magnetic configurations of BiMn2O5 using HSE. Experimental values correspond to the room temperature structure [34]. Magnetic configuration HSE Energy above hull, T=0K Space Group a b c Vol AFM-2 0 Pmc FM 5 Pbam AFM-1 13 Pbam FERRI 111 Pbam Exp 111 Pbam Table S2. Orientation, formation energy (surface energy above the hull), and work function for the 10 most stable low-index surface terminations found in this work for BiMn2O5.

9 Slab Orientation Formation energy (mev/f.u.) Work Function (ev) Average of 6 with surface energy <80 mev/f.u Table S3. Scanning droplet cell LED illumination sources, wavelengths, energies and corresponding figures. LED Part/Model/Geometry Wavelength (nm) Energy (ev) Irradiance (mw/cm 2 ) Figures ThorLabs M385F1/backside 385 ± ± , S1a ThorLabs M385F1/frontside 385 ± ± a ThorLabs M455F1/backside 455 ± ± , S1b ThorLabs M455F1/backside 455 ± ± S1c Doric LEDC4-385/Y/G/A_SMA [1] /frontside Doric LEDC4-385/Y/G/A_SMA [1] /frontside Doric LEDC4-385/Y/G/A_SMA [1] /frontside Doric LEDC4-385/Y/G/A_SMA [1] /frontside 387 ± ± a inset, S2 451 ± ± a inset, S2 515 ± ± a inset, S2 603 ± ± a inset, S2

10 Table S4: Electron and hole effective masses (Mij -1 =(1/ħ 2 )d 2 E/dkidkj) are computed using the PBEsol+U functional with U = 3.9 ev in units of electron rest mass (me). For each structure and edge state (VB and CB) we report the position, direction and value of the lightest mass. Mag. Config. CB position CB effect. mass direction CB effect. mass value (me) VB position VB effect. mass direction VB effect. mass value (me) AFM-2 R U 1.77 U R 1.69 FM Z G 0.5 G Z 0.64 AFM-1 Z G 1.88 G Z 1.89 FERRI G Y 0.69 Z G 1.87