Tuning the Electronic Structure of Cobalt Selenide on Copper Foam by Introducing a Ni Buffer Layer for Highly Efficient Electrochemical Water Splitting

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.

Self-Supporting Co/CeO2 Heterostructures for Ampere-Level Current Density Alkaline Water Electrolysis

Remodeling the active surface through fabricating heterostructures can substantially enhance alkaline water electrolysis driven by renewable electrical energy. However, there are still great challenges in the synthesis of highly reactive and robust heterostructures to achieve both ampere-level current density hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a new Co/CeO₂ heterojunction self-supported electrode for sustainable overall water splitting. The self-supporting Co/CeO₂ heterostructures required only low overpotentials of 31.9 ± 2.2, 253.3 ± 2.7, and 316.7 ± 3 mV for HER and 214.1 ± 1.4, 362.3 ± 1.9, and 400.3 ± 3.7 mV for OER at 0.01, 0.5, and 1.0 A·cm^-2, respectively, being one of the best Co-based bifunctional electrodes. Electrolyzer constructed from this electrode acting as an anode and cathode merely required cell voltages of 1.92 ± 0.02 V at 1.0 A·cm^-2 for overall water splitting. Multiple characterization techniques combined with density functional theory calculations disclosed the different active sites on the anode and cathode, and the charge redistributions on the heterointerfaces that can optimize the adsorption of H and oxygen-containing intermediates, respectively. This study presents the tremendous prospective of self-supporting heterostructures for effective and economical overall water splitting.