Amorphous Yolk–Shelled ZIF-67@Co₃(PO₄)₂ as Nonprecious Bifunctional Catalysts for Boosting Overall Water Splitting

Abstract

It is challenging to generate inexpensive and noble metal-free catalysts for efficient overall water splitting (OWS). To achieve this goal, suitable tuning of the structure and composition of electrocatalytic materials is a promising approach that has attracted much attention in recent years. Herein, novel hybrid amorphous ZIF-67@Co 3 (PO 4 ) 2 electrocatalysts with yolk−shell structures were prepared using a reflux method. It is demonstrated that yolk−shelled ZIF-67@Co 3 (PO 4 ) 2 is not only an active catalyst for the hydrogen evolution reaction (HER) but also an efficient catalyst for the oxygen evolution reaction (OER). The optimized composite electrode showed superior performance with low overpotentials of 73 and 334 mV @ 10 mA•cm −2 toward HER and OER, respectively, and a low potential of 1.62 V @ 10 mA• cm −2 and 1.66 V @ 30 mA•cm −2 in a practical OWS test under alkaline conditions. N−O bonds were formed to connect the two components of ZIF-67 and Co 3 (PO 4 ) 2 in the composite ZIF-67@Co 3 (PO 4 ) 2 , which indicates that the two components are synergistic but not isolated, and this synergistic effect may be one of the important reasons to boost the oxygen and hydrogen evolution performances of the hybrid. Based on experimental data, the high electrocatalytic performance was inferred to be related to the unique structure of ZIF-67, tuning the ability of Co 3 (PO 4 ) 2 and synergism between ZIF-67 and Co 3 (PO 4 ) 2 . The preparation strategy reported herein can be extended for the rational design and synthesis of cheap, active, and long-lasting bifunctional electrocatalysts for OWS and other renewable energy devices.

Strongly Coupled Nitrogen-Doped Mo2C@CoNi Alloy Hybrid Architecture toward Efficient Hydrogen Evolution Reaction

“…The detection of the N-Mo component is another direct proof of the successful preparation of nitrogen-doped Mo 2 C. The pyridinic N and graphitic N species in N-Mo 2 C@CoNi-650 can enhance the electrical conductivity. Particularly, the largest content of pyridinic N species is observed for N-Mo 2 C@CoNi-650 in Figure S6e, and it has been confirmed as advantageous for improving HER performance Figure f shows the O 1s high-resolution XPS spectrum of N-Mo 2 C@CoNi-650, in which the three peaks observed at 530.4, 531.2, and 532.9 eV correspond to the typical oxygen lattice in oxides, oxygen vacancy, and chemisorbed oxygen species, respectively.…”

“…Particularly, the largest content of pyridinic N species is observed for N-Mo 2 C@CoNi-650 in Figure S6e, and it has been confirmed as advantageous for improving HER performance. 19 Figure 2f shows the O 1s highresolution XPS spectrum of N-Mo 2 C@CoNi-650, in which the three peaks observed at 530.4, 531.2, and 532.9 eV correspond to the typical oxygen lattice in oxides, oxygen vacancy, and chemisorbed oxygen species, respectively. Indeed, a certain amount of oxygen vacancy is beneficial to HER performance, and the chemisorbed oxygen species may be used as the active sites for HER.…”

“…Accordingly, the enhanced HER performance can be assigned to the synergistic effect: (1) Based on the Volmer− Heyrovsky mechanism, the synergistic effect between each component can accelerate dissociation of water molecules; (2) the high conductivity of N-Mo 2 C@CoNi-650 can significantly promote the charge-transfer efficiency, resulting in improved HER performance; (3) the large ECSA value endows N-Mo 2 C@CoNi-650 with enhanced catalytic active site densities; (4) the pyridinic N present in N-Mo 2 C@CoNi-650 can donate an unpaired electron to an adjacent metal atom, providing positively charged metals as highly active catalytic sites for HER; 19 and (5) the smaller charge-transfer resistance and Tafel slope also promote the water dissociation process, which benefits the HER performance.…”

Electronic Structure Regulation of Nickel Phosphide for Efficient Overall Water Splitting

“…Exploitation and utilization of clean renewable energies are essential for the sustainable development of human society. , Because of its high energy density and zero carbon emissions, hydrogen is widely regarded as an efficient carrier of clean renewable energies . Water electrolysis is one of the most promising methods that convert unstable renewable energies into stable chemical hydrogen energy, , which can be realized by combining a water electrolyzer with renewable energy power systems. Generally, a water-splitting reaction can be divided into two half-reactions: the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) .…”

Construction of ZIF-67-On-UiO-66 Catalysts as a Platform for Efficient Overall Water Splitting

“…MOFs are self-assembled by metal ions and organic linkers . MOFs, as a new kind of crystalline material, have microporous hybrid organic–inorganic structures with diverse applications, such as detection, adsorption, proton conduction, catalysis, drug delivery, and so on, the properties of which are dependent on their structures including both compositions and architectures. − ZIF-67, a Co-MOF, has attracted much attention due to its well-tunable physical and chemical properties, but poor electrical conductivity, narrow micropore–distribution, and low porosity are its obvious shortcomings . UiO-66, a Zr-based MOF, has attracted immense research interest for its high porosity, thermal and chemical properties, aqueous, acid stability, mechanical stability, catalytic activity, high ion conductivity, and easy modification with a desired functionality compared to other common MOFs. − However, the activity and substrate specificity of pure monomeric MOFs still must be improved .…”