Amorphous Multi-elements Electrocatalysts with Tunable Bifunctionality toward Overall Water Splitting

Abstract

Economically producing hydrogen via electrocatalytic water splitting requires highly efficient and low-cost catalysts and scalable synthetic strategies. Herein, we present the preparation of hierarchically structured multi-elements water splitting electrocatalysts consisting of Fe, Co, Ni, S, P, and O with a one-step electrodeposition method. By tuning of the non-metal compositions of the catalysts, the electrochemical performances of the catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1 M KOH can be rationally modified, respectively. Under the optimum conditions, current densities of 100 and 1000 mA cm −2 were obtained at overpotentials of only 135 and 264 mV on the HER catalyst and 258 and 360 mV on the OER catalyst, respectively. When the best-performing HER and OER catalysts were assembled in a two-electrode system for overall water splitting, a current density of 10 mA cm −2 could be obtained under a cell voltage of 1.46 V with longterm durability. As far as we know, this is among the lowest voltages ever reported for a two-electrode electrolyzer based upon earth-abundant elements. Moreover, the catalysts can be facilely assembled on commercially available Ni mesh and demonstrate even higher performance, indicating their great potential for scaled-up water electrolysis. We further demonstrate that S and P play different and pivotal roles in modifying the apparent and intrinsic electrocatalytic activity of the as-prepared amorphous electrocatalysts, therefore pointing out a pathway toward the optimization of multi-elements catalysts.

Water Oxidation Catalysts for Artificial Photosynthesis

“…Co phosphides such as Co 2 P and CoP are also effective for electrocatalytic water oxidation, and ternary Ni 0.1 Co 0.9 P shows higher activity than the monometal counterparts ( Figure a) . In addition, multielements metal phosphides and sulfides consisting of Fe, Co, Ni, S, P, and O are efficient and stable WOCs in basic condition (Figure b,c), demonstrating an overpotential of only 258 and 360 mV at current densities of 100 and 1000 mA cm −2 , respectively . However, all these metal nitrides/phosphides/sulfides can be oxidized during the oxidation reaction, thus the actual active species may be the surface oxides.…”

“…Besides of metal oxides, other kinds of materials, such as metal phosphides, phosphites, sulfides, selinides, carbides, and nitrides are popular candidate for water oxidation. For instance, Ni 3 FeN nanoparticles exhibited high activity for water oxidation with a low overpotential of 280 mV at 10 mA cm −2 and a Tafel slope of 46 mV ∆ −1 , which was attributed to the intrinsic metallic character, the high electrical conductivity, good H 2 O adsorption property, and the highly exposed active sites .…”

“…c) Amperometric i – t curve of FeCoNiP 0.5 S 0.5 for the OER at 10 mA cm −2 . b,c) Reproduced with permission . Copyright 2018, American Chemical Society.…”

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

“…Moreover, the scarcity, high cost and poor durability seriously hamper large-scale application of noble metal-based materials. [12][13][14][15][16][17][18][19] Recently, due to the low cost and earth-abundant reserves, many efforts have been made to develop high activity non-noble metal based electrocatalysts. Non-noble transition metals such as Fe, Co, Ni and Mn have attracted a lot of attention, and the compounds of transition-metals have been suggested as replaceable electrocatalysts in OER.…”

Metal Doped Layered MgB2 Nanoparticles as Novel Electrocatalysts for Water Splitting

“…[11][12][13] . Unconventional and environmentally-benign H2 generation approaches encompass photo/electrolysis of water supported by renewable energy source (e.g., solar, geothermal) 3,14,15 . In fact, in large-scale hydrogen production, the advantages of electrochemical water splitting outweigh those of other conventional systems, including coal gasification and steam reforming of methane, because it has enormous amount of sources and easy to use without CO2 emission 13,16 .…”