3D-printed NiFe-layered double hydroxide pyramid electrodes for enhanced electrocatalytic oxygen evolution reaction

Abstract

Electrochemical water splitting has been considered one of the most promising methods of hydrogen production, which does not cause environmental pollution or greenhouse gas emissions. Oxygen evolution reaction (OER) is a significant step for highly efficient water splitting because OER involves the four electron transfer, overcoming the associated energy barrier that demands a potential greater than that required by hydrogen evolution reaction. Therefore, an OER electrocatalyst with large surface area and high conductivity is needed to increase the OER activity. In this work, we demonstrated an effective strategy to produce a highly active three-dimensional (3D)-printed NiFe-layered double hydroxide (LDH) pyramid electrode for OER using a three-step method, which involves direct-ink-writing of a graphene pyramid array and electrodeposition of a copper conducive layer and NiFe-LDH electrocatalyst layer on printed pyramids. The 3D pyramid structures with NiFe-LDH electrocatalyst layers increased the surface area and the active sites of the electrode and improved the OER activity. The overpotential (η) and exchange current density (i0) of the NiFe-LDH pyramid electrode were further improved compared to that of the NiFe-LDH deposited Cu (NiFe-LDH/Cu) foil electrode with the same base area. The 3D-printed NiFe-LDH electrode also exhibited excellent durability without potential decay for 60 h. Our 3D printing strategy provides an effective approach for the fabrication of highly active, stable, and low-cost OER electrocatalyst electrodes.

Tailoring 3D-Printed Electrodes for Enhanced Water Splitting

“…, Fe 2p 1/2 and Fe 2p 3/2 ) with a binding energy difference of 13.1 eV. Deconvoluted peaks can be assigned to Fe 3+ (711.3 and 724.4 eV) , and a satellite peak (∼718 eV), , which is attributed to the presence of iron oxides/hydroxides. ,, We note that similar spectral shapes and binding energies of high-valent iron species make it difficult to assign species as FeOOH or Fe 2 O 3 . , Finally, deconvoluted peaks from the O 1s spectrum (Figure S27c) can be assigned to M–O (528.4 eV), and M–OH (530.6 eV) , bonds and the peak at ∼532 eV can be assigned to adsorbed water. , The presence of Ni 2+ , Fe 3+ , and lattice oxygen from XPS results suggests that the NiFe electrocatalytic layer has a layered double hydroxide structure. , Since no additional peaks in the XRD pattern were seen and no peaks for metallic Ni (∼852.6 eV) , and Fe (∼705.5 eV) , were detected, it is likely that the surface NiFe LDH layer is amorphous. , …”

“…Furthermore, low relative standard deviations (RSD < 10%) from the error bars of our replicates in Figure f confirm the reproducibility of our deposition methodology. Hence, the Ni-PB electrode had the largest surface area due to the increased roughness, the fastest electron transfer, and the most hydrophilic surface, thereby increasing contact with the electrolyte and providing more active sites for water splitting. ,, …”

“…The electrode geometry is another extrinsic property that has been shown to influence the performance of water electrolysis. ,, We assessed the relationship between the electrode geometry and bubble release as a function of four macroscopic geometric patterns: cones, pyramids, cylindric rods, and elliptic (oval) cylinders (Figure a). Detailed properties of these patterns are shown in Table S1.…”

“…Maintaining OER stability is challenging due to the positive potentials that oxidize the Ni metal surface sites into a nickel oxide/hydroxide layer . OER cycling also induces structural changes due to the continuous reconstruction of layers exposed to the electrolyte, which increases the surface area and modifies material morphology .…”

“…Furthermore, ordered electrode structures with tailored geometries have been used to precisely characterize the relationship between electrode structure and electrochemical performance. , However, fabrication of complex electrode geometries is challenging via conventional methods . 3D printing has been utilized to circumvent this challenge and rapidly prototype complex and tailored designs with unique chemical and structural features. − Kou et al found that 3D-printed electrodes with ordered and periodic lattices suppressed bubble trapping and provided uniform flow compared to commercial nickel foam (NF) electrodes . Also, Paul et al demonstrated that patterning Ni surfaces with uniform arrays of cylindrical recesses and pillars through photolithographic techniques resulted in higher current densities relative to planar Ni electrodes .…”