Molybdenum and Phosphorous Dual‐Doped, Transition‐Metal‐Based, Free‐Standing Electrode for Overall Water Splitting

Abstract

Water splitting using earth-abundant, low-cost, highly efficient, transition-metal-based electrocatalysts with high activity and stability is inevitable for sustainable energy development. Herein, a molybdenum (Mo) and phosphorous (P) co-doped highly efficient and durable electrocatalyst is grown on nickel foam (P-NiCo 2 O 4 /CoMoO 4 /NF, for simplicity G-3) for hydrogen and oxygen evolution reactions (HER and OER, respectively). The dual doping of Mo and P prompts the formation of nanosheet array structures and modifies the surface electronic states, which subsequently enhance the active sites, facilitate the charge transfer, and accelerate the reaction kinetics. As a result, the G-3 sample requires a low overpotential of 78.7 mV and 248.6 mV to reach a current density of 25 mA cm À 2 for the HER and OER, respectively. Furthermore, a cell voltage of 1.729 V is required at 100 mA cm À 2 , and the catalyst demonstrates long-term stability of 54 h for overall water splitting.

Influence of Mo concentration on the structural and electrochemical properties of double-doped Mo–Co–Ni3S2/NF composites

“…Previous studies indicate that these two main splitorbit peaks are indicative of the hexavalent Mo 6+ oxidation state. 9,43,44 The S 2p spectrum resolution is high (Fig. 4d), showing two signals at 163.1 eV and 164.7 eV, corresponding to S 2p 3/2 and S 2p 1/2 states, 34,[45][46][47] and the peak at 169.8 eV is correlated with SO 4 2− , which is caused by surface oxidation.…”

“…where "M" represents the metal ions, and the theoretical values of the Volmer, Heyrovsky and Tafel reactions are 120, 40, and 30 mV dec −1 , respectively. 9 The reaction may follow one of the two reaction pathways i.e., the Volmer reaction can be followed by either the Heyrovsky or Tafel reaction. If Volmer adsorption process represents the rate-limiting step, the Tafel slope should be approximately120 mV dec −1 .…”

“…7 Platinum group noble metals are the most popular HER catalysts, but their high cost and limited availability inhibit widespread usage. [8][9][10][11] Hence, it is essential to unearth non-noble metal HER catalysts that are highperforming and exist in abundance on our planet, such as phosphides, 12 nitrides, 13 and sulfides 14,15 derived from transition metals.…”

Current Progress of Mo‐Based Metal Organic Frameworks Derived Electrocatalysts for Hydrogen Evolution Reaction

“…[80][81][82][83][84][85] Moreover, DFT calculations demonstrated that an effective "H delivery" transport channel existed in MoP, indicating its potential for HER. [86,87] Using NENU-5 as the precursor followed by carbonization, FeCl 3 etching and phosphorization by (NH 4 ) 2 HPO 4 as a P source, Li et al synthesized P-doped carbon encapsulated MoP (MoP@PC) for HER (Figure 7a). [88] Owing to the synergistic effect of P dopant, the high catalytic activity of MoP nanocrystal and the high porous carbon, the MoP@PC exhibited an onset potential of 97 mV for HER (Figure 7b), a small Tafel slope of 59.3 mV dec −1 , and good long-term durability for more than 1000 cycle (Figure 7c).…”

“…[ 80–85 ] Moreover, DFT calculations demonstrated that an effective “H delivery” transport channel existed in MoP, indicating its potential for HER. [ 86,87 ]…”