High-Performance Bifunctional Ni-Fe-S Catalyst in situ Synthesized within Graphite Intergranular Nanopores for Overall Water Splitting

Highly efficient sulfur-doped Ni3Fe electrocatalysts for overall water splitting: Rapid synthesis, mechanism and driven by sustainable energy

Designing efficient electrocatalysts and insight into their electrocatalytic mechanisms are significantly important for storing and converting the intermittent sustainable energy sources into clean hydrogen. In this study, we synthesize the bifunctional sulfur-doped Ni3Fe (NiFeS) electrocatalysts by a simple electrodeposition method only taking 30 s. After optimizing the components, it was found that the synthesized NiFeS electrocatalysts exhibit the excellent hydrogen and oxygen evolution reaction performances in 1.0 M potassium hydroxide solution. The results of experimental and theoretical calculations reveal that the introduced sulfur could optimize the electronic distribution, which make Ni electron-rich and Fe electron-deficient, thereby weakening the energy barriers of potential-determining steps, i.e. the absorption of H2O molecule on Ni sites for HER and formation of *OOH on Fe sites for OER, respectively. Besides, the NiFeS electrocatalysts are used as the bifunctional electrodes to water splitting, which only need 1.51 V to reach 10 mA·cm-2, and exhibits excellent durability and a >95% Faraday efficiency. Furthermore, the intermittent kinetic, wind and solar energies are used to power the assembled electrolyzer with NiFeS bi-electrodes to verify their great application potential. This work not only proved a deep insight into mechanism of the boosted electrocatalytic activities of NiFeS, but also the synthesized NiFeS electrocatalysts have great application prospect in the conversion of intermittent and sustainable energy sources into hydrogen by water electrocatalysis.

Highly clean and efficient iron phosphates modified by Ru nanocrystals for water oxidation

Optimizing the architecture of non-polluting, highly efficient, robust, and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is extremely crucial for accelerating the application of water splitting. Herein, a highly green and active OER electrocatalyst composed of Ru nanocrystal modified iron-rich phosphates is successfully developed via a hydrothermal and post-annealing approach. The eco-friendly phosphorus source of lecithin is employed to fabricate transition metal phosphates for the first time, which avoids the use of toxic and dangerous phosphorus sources. Meanwhile, it is found that Ru nanocrystals could form heterostructures with iron phosphates and induce conversion to iron-rich phosphates, which would greatly enhance the conductivity of the substrate and elevate the catalytic activity. As a result, overpotentials of only 250 mV and 290 mV are required to deliver 10 and 100 mA cm^-2 using this typical electrocatalyst. Also, the j-t curve shows no distinct variations in current over 45 h at a constant overpotential of 334 mV, indicating the outstanding activity and durability of the catalyst. Furthermore, nickel/cobalt-rich phosphates and phosphides were also acquired using similar experimental procedures, manifesting the wide applicability of Ru actuation. Hence, this work offers a convenient and scalable method for designing highly efficient, green, clean, and cost-effective electrocatalysts for water splitting.