D8 advance

X-ray diffraction (XRD, D8 ADVANCE, Bruker AXS, Karlsruhe, BW, Germany) analysis was recorded on a D8 ADVANCE X-ray diffractometer with Cu Kα radiation (λ= 1.5406 Å). The morphology of the sample was observed using a Leo 1530 vp scanning electron microscope (SEM, Zeiss, Oberkochen, BW, Germany).
The sample was adhered to the test bench with conductive adhesive for gold spraying; the operating voltage range was 10–20 kV. The thermal stability of the membranes was examined using thermal gravimetric analysis (TGA, STA449 C, NETZSCH, Selb, Bavaria, Germany) and differential thermal gravimetric (DTG). The tensile properties of materials were tested on an Instron 5566 universal testing machine (Intron, Boston, MA, USA). The tensile rate is 2.00 mm/min, the spline standard is 10×80 mm, and the film thickness is 0.50 to 0.80 mm.

For the analysis of mixed MOs on SBA-15, a Bruker D8 Advance powder diffractometer, operating with Ge-monochromated Cu Kα radiation (wavelength = 1.5406 Å) and a LynxEye linear detector. Data were collected over the angular range 5–85° in 2θ. For the analysis of pure ZnO and TiO₂, X-ray Diffraction (XRD) patterns were collected on a Bruker D8 Advance powder diffractometer with a sealed X-ray tube (copper anode, 40 kV and 40 mA) and a Si(Li) solid state detector (Sol-X) set to discriminate the Cu Kα radiation. Apertures of divergence, receiving, and detector slits were 2.0 mm, 2.0 mm, and 0.2 mm, respectively. Data scans were performed in the 2θ range 5–75° with 0.02° step size and counting times of 3 s per step. Quantitative phase analysis determination performed using the Rietveld method as implemented in the TOPAS v.4 program (Bruker AXS) using the fundamental parameters approach for line-profile fitting.

The microstructure of deposits was analyzed by scanning electron microscopy (SEM) (XL30ESEM-FEG; FEL, Amstelveen, Netherlands). The crystal phase and constituents of calcium phosphate coating were investigated by X-ray diffraction (XRD) (D8 Advance; Bruker, Karlsruhe, Germany) and Fourier transform infrared spectroscopy (FTIR) (D8 Advance; Bruker, Karlsruhe, Germany), respectively. Further, the hydrophilic property of implants was characterized by measuring the static water contact angles at room temperature.

The X-ray diffraction
patterns were recorded with a Bruker D8 Advance using a Cu X-ray source
in the Bragg–Brentano configuration with a variable primary
divergence slit using an energy-dispersive position-sensitive LynxEye
XE-T detector (Bruker). The powder measurements and the quantification
of the crystallinity were conducted by mixing a CeO₂ reference
(NIST SRM674b) and our powder sample in a 1:1 mass ratio. After rigorous
blending, the mixtures were deposited in a Si low background sample
holder. The mass fraction of the X-ray amorphous phase was calculated
via Rietveld refinement, in which the zero error, sample displacement,
lattice parameters, and size-induced broadening were taken into account.
The Rietveld refinement was jointly performed for the diffractograms
of the two Co₂FeO₄ samples mixed with the CeO₂ standard as well as for the pure CeO₂ standard
measured alone using the same structural parameters for the CeO₂ as well as the zero error and the background signals from
the sample holder.
To record the diffractograms of Co₂FeO₄ before and after OER, the samples were prepared on
a carbon foil (0.125 mm, 99.95% purity, GoodFellow) and measured with
a Bruker D8 Advance in parallel beam configuration with a Goebel mirror
and an equatorial Soller slit (0.3°). The applied electrochemical
protocol is described in Section 2.3.