P-bridged Fe-X-Co coupled sites in hollow carbon spheres for efficient hydrogen generation

Non-precious metals have shown attractive catalytic prospects in hydrogen production from ammonia borane hydrolysis. However, the sluggish reaction kinetics in the hydrolysis process remains a challenge. Herein, P-bridged Fe-X-Co coupled sites in hollow carbon spheres (Fe-CoP@C) has been synthesized through in situ template solvothermal and subsequent surface-phosphorization. Benefiting from the optimized electronic structure induced by Fe doping to enhance the specific activity of Co sites, bimetallic synergy and hollow structure, the as-prepared Fe-CoP@C exhibits superior performances with a turnover frequency (TOF) of 183.5 min-1, and stability of over 5 cycles for ammonia borane hydrolysis, comparable to noble metal catalysts. Theoretical calculations reveal that the P-bridged Fe-X-Co coupled sites on the Fe-CoP@C catalyst surfaces is beneficial to adsorb reactant molecules and reduce their reaction barrier. This strategy of constructing hollow P-bridged bimetallic coupled sites may open new avenues for non-precious metal catalysis.

Origin of the electrocatalytic oxygen evolution activity of nickel phosphides: in-situ electrochemical oxidation and Cr doping to achieve high performance

Zinc-air batteries (ZnABs) with high theoretical capacity and environmental benignity are the most promising candidates for next-generation electronics. However, their large-scale applications are greatly hindered due to the lack of high-efficient and cost-effective electrocatalysts. Transition metal phosphides (TMPs) have been reported as promising electrocatalysts. Notably, (Ni_1-xCr_x)₂P (0 ≤ x ≤ 0.15) is an unstable electrocatalyst, which undergoes in-situ electrochemical oxidation during the initial oxygen evolution reaction (OER) and even in the activation cycles, and is eventually converted to Cr-NiOOH serving as the actual OER active sites with high efficiency. Density functional theory (DFT) simulations and experimental results elucidate that the OER performance could be significantly promoted by the synergistic effect of surface engineering and electronic modulations by Cr doping and in-situ phase transformation. The constructed rechargeable ZnABs could stably cycle for more than 208 h at 5 mA cm^-2, while the voltage degradation is negligible. Furthermore, the developed catalytic materials could be assembled into flexible and all-solid-state ZnABs to power wearable electronics with high performance.

Synergistically coupling of Fe-doped CoP nanocubes with CoP nanosheet arrays towards enhanced and robust oxygen evolution electrocatalysis

The rational design of high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts for water splitting is of vital importance for development of renewable hydrogen energy. Herein, we demonstrate an interfacial engineering strategy to prepare Fe-doped CoP nanocubes/CoP nanosheet arrays heterostructure supported on carbon cloth (denoted as CoFeP/CoP/CC). The resultant CoFeP/CoP/CC heterostructure catalyst possesses abundant heterogeneous interfaces, which enables the exposure of reaction active sites and possibly modulation of electronic structure of the catalyst. Furthermore, this strong interfacial coupling of CoFeP and CoP as well as the integration structure on the carbon cloth guarantee high electronic conductivity and enhanced mechanical stability. Benefiting from these advantages, the CoFeP/CoP/CC-heterostructure exhibits high electrocatalytic OER performance with a low overpotential of 240 mV for reaching a current density of 10 mA cm^-2, which outperforms the commercial noble metal RuO₂ (255 mV) and many reported TMPs-based electrocatalysts. Moreover, this CoFeP/CoP/CC catalyst shows a remarkable OER catalytic stability over 100 h. This work provides an effective avenue for the design of the high-performance OER catalyst by interfacial engineering strategy.

Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes, serving as bifunctional electrocatalysts for overall water splitting. Notably, Mo doping could effectively modulate the electronic structure of NiCoP, leading to the increased electroactive site and improved intrinsic activity of each site. Furthermore, an electrochemical activation strategy is proposed to form Mo-doped (Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction. Benefiting from the unique freestanding structure and Mo doping, Mo-doped NiCoP and (Ni,Co)OOH show the remarkable electrochemical performances, which are competitive among current researches. In addition, an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm-2. Therefore, this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation.