Molybdenum carbide nanoparticles as a catalyst for the hydrogen evolution reaction and the effect of pH

Abstract

11Molybdenum carbide nanoparticles supported on carbon catalysts have been prepared 12 with a modified carbothermal reduction method. The soft carburization conditions of 13 this method allows the preparation of a nanoparticulate Mo2C even with high Mo 14 loading (50 wt%). The catalytic activity towards hydrogen evolution reaction was 15 analyzed both in an electrochemical cell at various pHs and in a laboratory-scale 16 electrolyser. These nanoparticles were found to be very active for catalyzing hydrogen 17 evolution reaction in acidic media and appeared to promote kinetics leaning towards the 18 Volmer-Heyrovský mechanism at low pH. Moreover, the Mo2C/C catalyst was shown 19 to be suitable for hydrogen production in the laboratory-scale electrolysis cell retaining 20 its performance during the four week durability experiment. Thus this study implies that 21 the investigated Mo2C/C electrocatalyst is a promising alternative for platinum as a 22 2 cathode material for electrolytic hydrogen production because of favorable kinetics and 23 stability. 24 25

A Redox‐anchoring Approach to Well‐dispersed MoCx/C Nanocomposite for Efficient Electrocatalytic Hydrogen Evolution

“…A Tafel plot of the catalyst reveals the rate‐limiting step in HER. Tafel slopes of 120, 40, 30 mV dec −1 correspond to the rate‐determing step of Volmer, Heyrovsky and Tafel reactions, respectively . Thus, the Tafel slope can be adopted as a guide to identify the HER mechanism.…”

Molybdenum Carbide‐Based Electrocatalysts for Hydrogen Evolution Reaction

“…[25] Meanwhile, researches have also shown that the measurement conditions including electrolytes with various pH values and temperatures as well as catalyst loading play important roles in affecting the current densities and Ta fel slopes toward HER. [26] As an important member of TMCs, Mo x Cw ere initially applied as catalysts to reactions such as alkanei somerization, [27,28] hydrogenation, [29] hydrodesulfurization and denitrification. [30,31] Mo x Ci tself is an extremelyh ard refractory ceramic material with an inherent bulk structure.…”

“…[75] At ypical example is carbon black (CB), which shows as uperior HER activity to unsupported Mo 2 C electrocatalyst. [26] Carbon nanotubes (CNTs) and carbon xerogel (CXG) are also reported to load Mo 2 C. [76] Compared to CB, onedimensional CNTs-supportedM o x Ce xhibit ab etter electrochemicalp erformance (Figure 5a-c), which is attributed to af aster kinetics that is characterized by al ower charge-transfer impedance of 21 W cm 2 of Mo 2 C/CNTs( vs. 36.1 W cm 2 of Mo 2 C/ CB). [77] However,M o 2 C/CNTsc atalyst exhibits al ower activity than Mo 2 C/CXG at mosto ft he potential ranges measured.…”

Ni‐Assisted Low Temperature Synthesis of MoCx with Enhanced HER Activity

“…[38] It is generallya ccepted that hydrogen evolution in acidic condition consists of two steps. [39] In Figure 5b,t he Tafel slope of Pt/C is 30 mV dec À1 ,c orresponding to aT afel mechanism. [8] Al ower Ta fel slope value of 82 mV dec À1 is obtained for MoC x /Ni-650, which suggests am ixed Volmer-Heyrovsky mechanism for HER.…”

“…The first is a proton adsorption with charge transfer step (Volmer reaction): H 3 O + +e − →H ads +H 2 O, while the second is a desorption step (Heyrovsky reaction): H ads +H 3 O + +e − →H 2 +H 2 O, or a recombination step (Tafel reaction): H ads +H ads →H 2 , where H ads represents H atoms adsorbed on the active sites of the catalyst. According to the kinetic model, Tafel slopes of 120, 40, 30 mV dec −1 correspond to the rate‐determining steps of Volmer, Heyrovsky and Tafel reactions, respectively . In Figure b, the Tafel slope of Pt/C is 30 mV dec −1 , corresponding to a Tafel mechanism .…”