Impact of morphology and oxygen vacancy content in Ni, Fe co-doped ceria for efficient electrocatalyst based water splitting

Designing a highly efficient, low-cost, sustainable electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water splitting is a current challenge for renewable energy technologies. This work presents a modified sol-gel route to prepare metal-ion(s) doped cerium oxide nanostructures as an efficient electrocatalyst for overall water splitting. Nickle (Ni) and iron (Fe) co-doping impacts the morphology in cerium oxide resulting in 5 nm nanoparticles with a mesoporous-like microstructure. The high level 20 mol% (1 : 1 ratio) of Ni + Fe bimetal-ion(s) doped CeO2 shows excellent HER and OER activities compared to the monodoped Fe/Ni and pristine CeO2. The co-doped catalysts required a low overpotential of 104 mV and 380 mV for HER and OER, respectively, in 1 M KOH, at a current density of 10 mA cm-2. The Tafel slopes of 95 mV dec-1 and 65 mV dec-1 were measured for HER and OER with the same representative samples which demonstrated excellent stability even after continuous operation for 20 hours in the alkaline medium. The unique morphology, enhanced oxygen vacancy (Ov) content and the synergistic effects of dopants in CeO2 play essential roles in enhancing the activities of Ni + Fe doped samples.

Cerium-Based Electrocatalysts for Oxygen Evolution/Reduction Reactions: Progress and Perspectives

Ce-based materials have been widely used in photocatalysis and other fields because of their rich redox pairs and oxygen vacancies, despite research on the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) remaining scare. However, most pristine cerium-based materials, such as CeO₂, are non-conductive materials. Therefore, how to obtain highly conductive and stable OER/ORR electrocatalysts is currently a hot research topic. To overcome these limitations, researchers have proposed a variety of strategies to promote the development of Ce-based electrocatalysts in recent years. This progress report focuses on reviewing new strategies concerning three categories of Ce-based electrocatalysts: metal-organic framework (MOF) derivatives, structure tuning, and polymetallic doping. It also puts forward the main existing problems and future prospects. The content of cerium in the crust is about 0.0046%, which is the highest among the rare earth elements. As a low-cost rare earth material, Ce-based materials have a bright future in the field of electrocatalysis due to replacing precious metal and some transition metals.

Bionic Preparation of CeO2-Encapsulated Nitrogen Self-Doped Biochars for Highly Efficient Oxygen Reduction

This study reports the superior performance of novel carbonaceous materials, CeO₂-encapsulated nitrogen-doped biochars [BC-Ce-X (X = 1 and 2)], for oxygen reduction reaction (ORR). The biomass precursor of this value-added biochar material was biomimetically prepared via a hydroponic operation in the Ce-enriched solution. The characterization results showed that CeO₂ with large amounts of oxygen vacancies was stably embedded in the N self-doped biochars during the pyrolytic processes. The measured specific surface areas of cerium-free biochar (BC sample), BC-Ce-1, and BC-Ce-2 were 79, 566, and 518 m²/g, respectively. The BC-Ce-X (X = 1 and 2) showed excellent ORR performances with onset potentials of ∼0.90-0.91 V, which outperformed the commercial 10 wt % Pt/C and BC. Compared with Pt/C, the BC-Ce-2 had better methanol tolerance and stability. Also, BC-Ce-2 displayed excellent electrochemical activity for Zn/air batteries. Controlled experiments and density functional theoretical calculations illustrated the synergistic effect between the pyri-N/C centers and CeO₂ with oxygen vacancies in ORR. The Lewis base sites, created by pyri-N and oxygen vacancies, greatly facilitated the chemisorption of O₂ molecules.

Urea-assisted enhanced electrocatalytic activity of MoS2–Ni3S2 for overall water splitting

Urea-assisted enhanced electrocatalytic activity of MoS₂–Ni₃S₂ as a bifunctional electrocatalyst for overall water splitting.