Fe‐doped CoNi_0.5P Hierarchical Arrays as Efficient Bifunctional Electrocatalysts for Overall Water Splitting: Evolution of Morphology and Coordination of Catalytic Performance

Abstract

Design and synthesis of bifunctional electrocatalysts with high efficient and durability for electrolytic water splitting still remain an important matter for the research of renewable energy systems. Herein, a series of CoNi 0.5 Fe x P/CC (x = 0, 0.08, 0.125, 0.25, 0.5) catalysts have been successfully prepared by a simple hydrothermal and phosphorization process, and directly used as bifunctional electrocatalysts for OER and HER. Benefiting from the suitable Fe element doping content and novel nanowire-nanosheet co-existent hierarchical nanostructure, the optimal CoNi 0.5 Fe 0.125 P/CC catalyst shows an outstanding bi-functional catalytic performance, with 344 mV low overpotential to reach at 100 mA cm À 2 during OER process and 74 mV overpotential to reach at 10 mA cm À 2 during HER process. The water electrolysis device employing CoNi 0.5 Fe 0.125 P/CC as cathode and anode at the same time, it only requires as low as 1.61 V of voltage to achieve the current density of 10 mA cm À 2 in alkaline solution, implying a great practical application value of this novel hierarchical nanostructured material for overall water splitting.[a] W.

Ammonium Nitrate‐Assisted Low‐Temperature Synthesis of Co, Co2P@CoP Embedded in Biomass‐Derived Carbons as Efficient Electrocatalysts for Hydrogen and Oxygen Evolution Reaction

“…[4][5][6] The negatively charged P atoms in TMPs can not only capture protons as Lewis bases, but also effectively promote the desorption of H 2 from the active sites. Particularly, recent studies have shown that cobalt phosphides could act as bifunctional catalysts toward HER and OER, [7,8] through heteroatoms doping, [9,10] MOF coupling, [11,12] anodic electrochemical treating, [13] and hetero-structure engineering. [14] Preparation of cobalt phosphides generally involves two key procedures.…”

Earth-Abundant Fe and Ni Dually Doped Co2P for Superior Oxygen Evolution Reactivity and as a Bifunctional Electrocatalyst toward Renewable Energy-Powered Overall Alkaline Water Splitting

“…Comparing LSV curves in Figure 6a, two major conclusions could be reached: (i) the phosphide electrocatalysts apparently reveal superior OER performance to their corresponding S6 in the Supporting Information) and outperforms most of the previously reported OER electrocatalysts, including some phosphides and their composites regarding η 100 , such as NiCoP@NiMn LDH, 7 Mo-doped CoP, 33 Fe-doped CoNi 0.5 P hierarchical arrays, 34 N-doped Ni-Co phosphide, 35 Ni-Co/Ni-Fe phosphides, 36 Mo-doped NiCoP nanosheet arrays, 37 Fe-doped Ni-Co phosphide nanoplates, 38 and hollow Fe-Co-P alloy nanostructures. 39 More detailed comparisons are summarized in Table S3 in the Supporting Information.…”

“…The FeNi-Co 2 P electrocatalyst reveals a current density of 96.2 mA/cm 2 , 137 times higher than that of Ni-Co 3 O 4 (0.7 mA/cm 2 ) and 8.9 times and 15.3 times higher than those of FeNi-Co 3 O 4 (10.8 mA/cm 2 ) and Ni-Co 2 P (6.3 mA/cm 2 ), respectively. It is noteworthy that the FeNi-Co 2 P electrocatalyst surpasses the benchmark OER catalyst RuO 2 (η 10 = 275 mV, see Figure S6 in the Supporting Information) and outperforms most of the previously reported OER electrocatalysts, including some phosphides and their composites regarding η 100 , such as NiCoP@NiMn LDH, Mo-doped CoP, Fe-doped CoNi 0.5 P hierarchical arrays, N-doped Ni-Co phosphide, Ni-Co/Ni-Fe phosphides, Mo-doped NiCoP nanosheet arrays, Fe-doped Ni-Co phosphide nanoplates, and hollow Fe-Co-P alloy nanostructures . More detailed comparisons are summarized in Table S3 in the Supporting Information.…”

“…Both Ni-Co 3 O 4 (74.6 mV/dec) and Ni-Co 2 P (64.8 mV/dec) electrodes show the Tafel slope between 12 and 60 mV/dec, indicating that the OER process is rate-limited at the deprotonation process for forming the intermediate O* owing to the strong interaction between OH* with the surface cations on these two electrodes. On the other hand, the much smaller Tafel slopes in FeNi-Co 3 O 4 (47.3 mV/dec) and FeNi-Co 2 P (42.8 mV/dec) electrodes predict that Fe incorporation moves the rate-limiting step forward to the formation of the O–O bond (step 3), the most challenging step for the regular oxide OER electrocatalysts. ,, This is attributed to the electronic reconfiguration on the reactive center caused by Fe doping, which moderates the OH* interaction and thermodynamically promotes the formation of OOH* on the surface in both oxide and phosphide. ,− …”

Recent Progresses in Engineering of Ni and Co based Phosphides for Effective Electrocatalytic Water Splitting

“…Similar kind of study by Wenzhuo et al . with the increased activity trend was observed in the Fe doping CoNi 0.5 Fe 0.125 P/CC as an electrocatalyst alkaline water electrolysis [132] . Here, the same kind of synthesis was followed such as hydrothermal followed by phosphorization which results sheet like morphology.…”