Hexagonal-Phase Cobalt Monophosphosulfide for Highly Efficient Overall Water Splitting

Abstract

The rational design and synthesis of nonprecious, efficient, and stable electrocatalysts to replace precious noble metals are crucial to the future of hydrogen economy. Herein, a partial sulfurization/phosphorization strategy is proposed to synthesize a nonstoichiometric pyrrhotite-type cobalt monophosphosulfide material (CoSP) with a hexagonal close-packed phase for electrocatalytic water splitting. By regulating the degree of sulfurization, the P/S atomic ratio in the cobalt monophosphosulfide can be tuned to activate the Co/Co couples. The synergy between the nonstoichiometric nature and the tunable P/S ratio results in the strengthened Co/Co couples and tunable electronic structure and thus efficiently promotes the oxygen/hydrogen evolution reaction (OER/HER) processes toward overall water splitting. Especially for OER, the CoSP material, featured with a uniform yolk-shell spherical morphology, shows a low overpotential of 266 mV at 10 mA cm (η) with a low Tafel slope of 48 mV dec as well as high stability, which is comparable to that of the reported promising OER electrocatalysts. Coupled with the high HER activity of CoSP, the overall water splitting is demonstrated with a low η at 1.59 V and good stability. This study shows that phase engineering and composition control can be the elegant strategy to realize the Co/Co couple activation and electronic structure tuning to promote the electrocatalytic process. The proposed strategy and approaches allow the rational design and synthesis of transition metal monophosphosulfides toward advanced electrochemical applications.

Engineering Ternary Pyrite‐Type CoPS Nanosheets with an Ultrathin Porous Structure for Efficient Electrocatalytic Water Splitting

“…Here, the electronic properties were investigated through temperature-dependent resistance measurement. Our CoPS UPNSs are different from the most reported cobalt phosphosulfide electrocatalysts, such as the nonstoichiometric Co 0.9 S 0.58 P 0.42 with a hexagonal close-packed phase, [14] Co 2À x SP nanosheets/CFP [17] , or (CoS j P) nanoparticles, [31] because their crystal structure is similar to Co 1À x S. It turns out that the substitution of half the S atoms by P does change the electron structure, confirming the theoretical prediction.…”

“…For example, Sun et al proposed the topotactic conversion preparation of various transition metal phosphides as water splitting electrocatalysts. [10][11][12][13][14] Density function theory (DFT) calculations have revealed that replacing S with the less electronegative P in the CoS 2 could tune the CoS 2 electronic structure to a more thermo-neutral hydrogen adsorption at the active sites and thus enhance HER activity. Very few catalysts can perform both HER and OER in wide pH ranges.…”

“…Recently, Cao et al reported Co corroles as efficient HER and OER catalysts in the pH range of 0-14. Other studies of nonstoichiometric cobalt phosphosulfide toward OER performance are based on Co 1-x S-like structures, [14,17] but what remains to be studied is the change of electronic structure in CoPS and its underlying correlation with OER performance when half of S is replaced with P in CoS 2 . Among the nonnoble electrocatalysts, transition metal (Fe, Co, Ni) phosphosulfides as OER or HER catalysts inspire great interest because of their superior catalytic activity.…”

“…[19][20][21] With the addition of porous structure, such nanosheets can expose more active sites and facilitate electron transport, which can effectively boost the electrocatalytic activity. [14] Nonetheless, its catalytic efficiency still needs to be improved. [14] Nonetheless, its catalytic efficiency still needs to be improved.…”

Metall‐Phosphor‐Trichalkogenide (MPCh3): von der Synthese zu aktuellen Energieanwendungen

“…Der Degradationsgrad kann vom verwendeten Medium abhängen. [21,22,37,40,42,43,45,47,65,67,68] In Analogie zur HER hat MPSe 3 -Volumenmaterial ein geringeres Onset-Potential als MPS n ,j edoch sind die Ausbeuten bei weitem nicht konkurrenzfähig,u nd die Stabilitäti st sehr mangelhaft. Die XPS-Untersuchung des BiPS 4 -Materials zeigte eine vollständige ¾nderung seiner Zusammensetzung unter Komplettverlust des P. [21] Die MPSe 3 -Materialien waren in alkalischen Medien weniger stabil als in sauren, wobei FePSe 3 und MnPSe 3 jedoch den anderen Verbindungen überlegen waren und deshalb als die beiden interessantesten Vertreter der untersuchten Reihe gelten (Abbildung 4i,j).…”