Prereduction of Metal Oxides via Carbon Plasma Treatment for Efficient and Stable Electrocatalytic Hydrogen Evolution

Abstract

Prereduction of transition metal oxides is a feasible and efficient strategy to enhance their catalytic activity for hydrogen evolution. Unfortunately, the prereduction via the common H annealing method is unstable for nanomaterials during the hydrogen evolution process. Here, using NiMoO nanowire arrays as the example, it is demonstrated that carbon plasma (C-plasma) treatment can greatly enhance both the catalytic activity and the long-term stability of transition metal oxides for hydrogen evolution. The C-plasma treatment has two functions at the same time: it induces partial surface reduction of the NiMoO nanowire to form Ni Mo nanoclusters, and simultaneously deposits a thin graphitic carbon shell. As a result, the C-plasma treated NiMoO can maintain its array morphology, chemical composition, and catalytic activity during long-term intermittent hydrogen evolution process. This work may pave a new way for simultaneous activation and stabilization of transition metal oxide-based electrocatalysts.

Synergistic Doping and Intercalation: Realizing Deep Phase Modulation on MoS2 Arrays for High‐Efficiency Hydrogen Evolution Reaction

“…In particular,t he d-band center of (N,PO 4 3À )-MoS 2 is far lower than that of 2H-MoS 2 , revealing that (N,PO 4 3À )-MoS 2 with more electron filling of the antibonding states greatly promotes the hydrogen adsorption/desorption from HER catalyst surface.T he hydrogen adsorption free energy (DG H )i sf urther calculated to illustrate the hydrogen evolution activity (Figure 5f). [45] The calculated DG H of 2H-MoS 2 ,PO 4 3À -MoS 2 ,N-MoS 2 ,1TMoS 2 , and (N,PO 4 3À )-MoS 2 is À2.08 eV, À0.41 eV, À0.21 eV,0.11 eV, and 0.07 eV,r espectively.I tc onvincingly demonstrates that (N,PO 4 3À )-MoS 2 is more favorable for hydrogen adsorption/ desorption, superior to other counterparts and even better than pure 1T MoS 2 .Owing to the metallic property,lowest dband center and smallest hydrogen adsorption/desorption energy,t he as-prepared (N,PO 4 3À )-MoS 2 dramatically improves the HER catalytic activity.…”

“…[33][34][35] Then egligible HER activity of VG skeleton suggests that the VG is mainly used as ah ighly conductive support for active MoS 2 nanosheets.The excellent catalytic performance of (N,PO 4 3À )-MoS 2 /VGisattributed to the synergistic doping-intercalation effect and higher proportion of 1T-MoS 2 .T he HER performance of (N,PO 4 3À )-MoS 2 / VG is also better than those of reported Mo-based materials (Figure 4c)r eported previously. [36][37][38][39][40][41][42][43][44] To eliminate the influence of surface area and reveal the intrinsic catalytic behavior, turnover frequency (TOF) is calculated to gain the intrinsic per-site activity, [28,45] as shown in the Supporting Information, Figure S15. Impressively,t he TOFv alues of (N,PO 4 3À )-MoS 2 /VGa re larger than those of MoS 2 /VG, N- intercalation can essentially promote the activity for HER catalysis.T he cycling durability test was carried out at 10 mA cm À2 for 10 h, and there is no obvious decay observed for the all electrodes (Figure 4d), suggesting their excellent long-term stability.M oreover,c omparatively,t he S2pa nd Mo 3d XPS spectra of (N,PO 4 3À )-MoS 2 /VGa fter 1000 cycles (Supporting Information, Figure S16) do not change and all characteristic peaks are noticed, demonstrating its excellent stability.Furthermore,SEM image (Supporting Information, Figure S17) after 10 hs tability test reveals that the morphology of (N,PO 4 3À )-MoS 2 /VGa rray is well maintained, further suggesting its excellent structure stability.T ofurther study the superior HER performance of the (N,PO 4 3À )-MoS 2 /VG electrode,t he effective electrochemical active surface areas (ECSA) of these electrodes were calculated by monitoring the double-layer capacitance (C dl )according to the CV results at different scan rates (Supporting Information , Figure S18).…”

Applications of Plasma in Energy Conversion and Storage Materials

“…By optimizing the plasma conditions, they were able to achieve a record selectivity toward ethylene (60%) with a low overpotential on the plasma‐activated Cu catalysts. On the other hand, Zhang et al demonstrated a surface reduction method to boost the HER performance of NiMoO 4 ( Figure 14 a) through carbon RF plasma . They found that the C plasma treatment not only induces partial surface reduction of the NiMoO 4 nanowires to form Ni 4 Mo nanoclusters, but also deposits a thin graphitic carbon shell, which greatly improves the long‐term stability of the oxides catalysts for HER.…”

“…b) LSV curves of C plasma treated NiMoO 4 for HER in 1 m KOH. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

Modulating electronic and geometric structure of transition metal compounds for efficient water splitting

“…Furthermore, H2O is both the raw material and the only product. 18 Water splitting is a strong uphill reaction with a theoretic decomposition voltage of 1.23 V. In the case of standard conditions (1 atm and 298 K), the increase of Gibbs free energy (ΔG = nFE°) in this uphill reaction is 237.1 kJ mol -1 , where E° is the theoretical decomposition voltage (1.23 V), n is the transferred electrons number (n=2), and F is the Faraday constant (96485 C mol -1 ). In addition, the transportation of electron at the electrode/electrolyte interface leads to energy loss, and thus results in the sluggish kinetics of water splitting process.…”