Atomically Dispersed Mo Supported on Metallic Co₉S₈ Nanoflakes as an Advanced Noble‐Metal‐Free Bifunctional Water Splitting Catalyst Working in Universal pH Conditions

Abstract

sunlight for sustainable energy conversion and storage. [1] For renewable and efficient hydrogen production, electrochemical water splitting employing renewable electrical energy is a promising route due to its inherent advantages, including readily available reactant, stable output, and feasibility of large-scale production. [2] However, the large overpotential (η) of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) greatly limited their practical applications. Moreover, due to the thermodynamic limitation, the HER reaction usually prefers to be conducted under strong acidic solution while the OER is conducted under basic solution. [3] Extra energy needs to be supplied in order to maintain the pH differences between those two reactions. It is thus imperative to develop highly active electrocatalysts that can utilize under a wide pH range. At present, the state-ofthe-art electrocatalysts for HER are precious metal Pt-based materials and for OER are costly Ir-or Ru-based oxides. [4] But the high cost, scarcity and unsatisfactory durability of above mentioned catalysts further limit the practical utilization of the water splitting technology. [5] Water splitting requires development of cost-effective multifunctional materials that can catalyze both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) efficiently. Currently, the OER relies on the noble-metal catalysts; since with other catalysts, its operation environment is greatly limited in alkaline conditions. Herein, an advanced water oxidation catalyst based on metallic Co 9 S 8 decorated with single-atomic Mo (0.99 wt%) is synthesized (Mo-Co 9 S 8 @C). It exhibits pronounced water oxidization activity in acid, alkali, and neutral media by showing positive onset potentials of 200, 90, and 290 mV, respectively, which manifests the best Co 9 S 8 -based singleatom Mo catalyst till now. Moreover, it also demonstrates excellent HER performance over a wide pH range. Consequently, the catalyst even outperforms noble metal Pt/IrO 2 -based catalysts for overall water splitting (only requiring 1.68 V in acid, and 1.56 V in alkaline). Impressively, it works under a current density of 10 mA cm −2 with no obvious decay during a 24 h (0.5 m H 2 SO 4 ) and 72 h (1.0 m KOH) durability experiment. Density functional theory (DFT) simulations reveal that the synergistic effects of atomically dispersed Mo with Co-containing substrates can efficiently alter the binding energies of adsorbed intermediate species and decrease the overpotentials of the water splitting.

Corrosion Engineering on Iron Foam toward Efficiently Electrocatalytic Overall Water Splitting Powered by Sustainable Energy

“…As displayed in Figure a, a low cell voltage of only 1.46 V was required for the electrolyzer to deliver a current density of 10 mA cm –2 which is superior to Pt/C/FF||RuO 2 /FF with 1.52 V (Figure S15, Supporting Information). The electrolyzer composed of FFNaRu and FFNaNi presented electrocatalytic performances comparable to previous materials, such as a‐RuTe 2 PNR, [ 11d ] NiFeRu‐LDH, [ 20 ] Mo‐Co 9 S 8 @C, [ 21 ] Pt‐CoS 2 /CC, [ 22 ] CoFeZr oxides/NF, [ 2a ] Ir/MoS 2 /CF, [ 23 ] Ru NP/C+NiFe LDH, [ 24 ] RuCu NSs/C, [ 25 ] and CoFe‐CDs+CoFeRu@C [ 26 ] (Figure 6b) and other reported nanomaterials (Table S3, Supporting Information). Moreover, the long‐term stability at a current density of 10 mA cm –2 showed negligible current loss after 12 h, demonstrating its superior overall water‐splitting durability (Figure 6c).…”

Trifunctional Single‐Atomic Ru Sites Enable Efficient Overall Water Splitting and Oxygen Reduction in Acidic Media

“…In principle, the difference in the adsorption energies between ΔG O* and ΔG OH* is suggested to be a descriptor for estimating the catalytic capability for OER. [52] Ru-SA/Ti 3 C 2 T x exhibits a lower ΔG O* −ΔG OH* value Figure 7. DFT calculation results.…”

Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment

“…Sun and co-workers also found the possible Mo and Co dual-sites mechanism, as the Mo-enhanced Co synergistic active sites are more competitive than the single Mo and Co sites (Figure 2d,e). [54] With the aid of surface X-ray scattering technique at welldefined catalyst surface, Shao-Horn and co-workers have experimentally identified the reaction pathways of OER at RuO 2 in acid, and proposed a modified mechanism, which is different from the traditional AEM (Figure 2f). [55] The RuO 2 exposes two different Ru sites, i.e., a coordinatively unsaturated site (CUS) bound with five O atoms and a bridge site (BRI) coordinated with six O atoms.…”