Air-stable phosphorus-doped molybdenum nitride for enhanced electrocatalytic hydrogen evolution

Abstract

Molybdenum-based electrocatalysts for hydrogen evolution have been investigated extensively in recent years. However, unlike other non-oxides, molybdenum nitride generally shows a weak preference for hydrogen evolution and low performance owing to surface oxidation and the strong Mo-H bond. Here, we prepare an air-stable molybdenum nitride through a multi-step solid-state reaction. We find that a uniformly dispersed mixture of the precursors is optimal for preparation of the electrocatalyst. To further enhance hydrogen evolution performance towards practical device applications, phosphorus doping is carried out, using a few layered black phosphorus source. The phosphorus-doped molybdenum nitride (P-Mo-N) sample catalyzes hydrogen evolution with potentials of 105, 145, and 157 mV at the current densities of 10, 50, and 100 mA/cm 2 , respectively, in 0.5 M H 2 SO 4 solution with a small Tafel slope of 43 mV/dec. Thus it outperforms many of the state-of-art molybdenum-based hydrogen evolution catalysts reported to date.

Dual Doping Induced Interfacial Engineering of Fe2N/Fe3N Hybrids with Favorable d‐Band towards Efficient Overall Water Splitting

“…Compared to other transition metal compounds, transition‐metal nitrides (TMNs) have its special features of high electrical conductivity . Despite the challenges in terms of enhancing the performance of TMNs, nitrides of Ni, Co, Mo, and W have been reported as HER catalysts in alkaline solution but greater challenges still hold. Wang's group pointed out that the unfavorable d‐band energy level results in poor HER catalytic behavior .…”

Metal-doped Mo2C (metal = Fe, Co, Ni, Cu) as catalysts on TiO2 for photocatalytic hydrogen evolution in neutral solution

“…As shown in Figures S3a-e, the bare Mo2C has a bulky shape, confirming that the high-temperature solid-state reaction will induce the created particle aggregation. Moreover, the precursor of MoO3 is the typical thick-layered structure [27,50]. Similarly, the metal-doped Mo2C samples show the bulk morphology with the small particles, further suggesting a strong reaction between MoO3 and urea.…”

“…Clearly, the five samples show the semicircle change with a specific trend. It was reported that the radius of the arc translates into the relative impedance of the carrier interface migration [27,28], and evidently, the Cu-doped sample gives the smallest interface impedance. Specifically, the EIS spectra were fitted using the circuit model, as shown in Figure S6.…”

“…Typically, CV was carried out at different scan rates of 20, 40, 60, 80, and 100 mV/s in the range of 1.2-1.4 V vs. RHE, as shown in Figure S7. The plots of ∆j at 1.3 V vs. RHE against the scan rate are shown in Figure 4e, and the slopes were used to express double the Cdl values [27,28]. The Cdl values were calculated to be 0.047, 0.06, 0.1, 0.16, and 0.24 F/cm 2 for Mo2C, Fe-Mo2C, Co-Mo2C, Ni-Mo2C, and Cu-Mo2C, respectively (Table 1).…”

“…Doping is known to weaken or strengthen the surface adsorption energy between materials and reaction intermediates [26][27][28][29][30]. It can also form additional energy levels near the Efermi and change the electrode interfacial dipole layer to some extent [31][32][33].…”