The rational design of heterogeneous catalysts is the key to achieving optimal physicochemical properties and high electrochemical activity. However, the development of new amorphous heterostructures is more challenging than existing crystalline-crystal heterostructures. To overcome these problems, this paper reports a synergistic auxiliary strategy that can help fabricate amorphous Nio crystal Niceox (A-Nio C-Niceox) heterostructures. The coordination geometry of organic ligands plays a key role in the formation of coordination polymers with high nickel content. This, therefore, provides an opportunity for nickel to be supersaturated in the Niceox structure, resulting in endogenous spillover of nickel from the depths of Niceox to its surface. The heterostructure is characterized by strong coupling of amorphous NIO and crystalline NICEOX, and exhibits harmonious interaction, low overpotential, and high catalytic stability in the oxygen evolution reaction (OER). Theoretical calculations show that the amorphous interface is conducive to charge transfer, which plays a key role in regulating the local electron density of the Ni site, thereby promoting the adsorption of oxygen-based intermediates at the Ni site and reducing the energy barrier related to dissociation. Overall, this study highlights the potential to harmonize different metal ions at the molecular level to advance the design of amorphous heterostructures.
Schematic diagram of the synthesis of C-Niceox and A-Nio C-Niceox. The cyan, red, gray, and light gray spheres in the chemical representation of ligands represent n, o, c, and h atoms, respectively.
A) PXRD profiles of NICE-CPS (1:1) and NICE-CPS (6:1) (thin color and thick black profiles, respectively) were obtained and simulated. b) PXRD spectra of Nio CEO2, C-Niceox, and A-Nio C-Niceox. c) SEM image of A-NIO C-Niceox, illustrated as the corresponding cross-section. d) TEM image, e) EDS-based element diagram, f) A-NIO C-Niceox HAADF-STEM image. G, H) HR-TEM image of A-Nio C-Niceox, the insertion of (G) shows the corresponding SAED pattern. i, k) corresponding enlarged images and fft plots of representative amorphous nio and crystalline c-niceox domains in j, l) (h).
a) Raman spectra of CEO2, C-Niceox and A-Nio C-Niceox. b,c) Raman spectra of A-Nio C-Niceox and C-Niceox with increasing and then decreasing applied laser power. d) Raman spectra of a-nio c-niceox-y. e) Relationship between the intensity ratio (D) of the DF2G band and the feed ratio of Ni CE. f) Band structures of CEO2, NIO, and A-Nio C-Niceox (CB: conduction band; vb: valence band). g) High-resolution CE 3D XPS profiles of CEO2 and A-Nio C-Niceox. h) High-resolution NI 2P XPS profiles of NIO and A-NIO C-Niceox. i) High-resolution O-1S XPS spectra of CEO2, NIO, and A-NIO C-Niceox.
A) LSV polarization curves of NIO, physically mixed NIO CEO2, IRO2, A-NIO C-Niceox, A-NIO C-Niceox-Y series samples in 1 M KOH solution. b) overpotential, c) Tafel diagram. (The army blue, dark khaki, dark sky blue, orange, pink, medium purple, and dark cyan in Figure (b, c) represent NIO, A-NIO C-Niceox -1, A-NIO C-Niceox -2, A-NIO C-Niceox -3, A-NIO C-NICEOX, A-NIO C-NICEOX -4, and A-NIO C-NICEOX -5, respectively.) d) at a positive potential of 1EIS curves obtained at 53 V, e) CDL values for NIO, A-NIO C-Niceox, and A-NIO C-Niceox-Y series samples. F) Time-potential-based A-Nio C-Niceox stability test, performed at 10 mA cm2 in 1 M Koh, inset showing the LSV polarization curves of A-Nio C-Niceox before and after 500 cycles. g) in 1Under the condition of 0 m KOH, the contour plot corresponding to A-Nio C-Niceox was obtained by in-situ electrochemical Raman spectroscopy at different potentials (vs RHE). High-resolution H)Ni2P and I)O1S XPS spectra of A-Nio C-Niceox before and after electrochemical testing.
A) the difference in charge density between Ni-doped CeOX and B) A-NiO C-Niceox with an amorphous NiO surface. C) Band structure of A-Nio C-Niceox, D) ELF plot, E) DOS. f) Ni site free energy diagram of A-Nio, C-Niceox and C-Niceox in OER.
In this study, polydentate ligands with different active functional groups (carboxyl and amino groups) were selected, which have different coordination capacities for rare earth and transition metal ions, so the coordination structure can be controlled by adjusting the feed ratio of metal ions. During the collapse process, the highly metal-loaded structure successfully transforms from a solid solution to a heterogeneous structure. Specifically, the introduction of abundant Ni into the NICE-CP framework via coordination bonds induces the formation of a solid solution in NiceOx after annealing and enhances the supersaturation and endogenous spillover of Ni in NiceOx. In addition, CEOx induces amorphization of NIO, resulting in the formation of a heterostructure consisting of amorphous NIO and crystalline NICEOX. This demonstrates the role of coordination chemistry in the construction of amorphous heterostructures. Thanks to the good amorphous interface and Ni-Ce interaction microenvironment, the A-Nio C-Niceox heterostructure has a low overpotential at an OER current density of 10 mAcm2. Theoretical calculations help attribute superior OER activity to the activation of local electronic properties at the Ni site, which is facilitated by charge transfer at the interface. This synergistic assistance strategy provides a new way for the development of efficient heterostructures in stage engineering systems. In addition, considering the design flexibility of organic ligands and the diversity of coordination modes, it can be used as a general method for the precise synthesis of amorphous heterostructures using heterometallic CPS.
a coordination‐derived cerium‐based amorphous–crystalline heterostructure with high electrocatalytic oxygen evolution activity - an - small - wiley online library