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1. Unexpected Correlation Between Boron Chain Condensation and Hydrogen Evolution Reaction (HER) Activity in Highly Active Vanadium Borides: Enabling Predictions

   https://doi.org/10.1002/ange.202000154  

   Lee, Eunsoo ; Park, Hyounmyung ; Joo, Hyunkeun ; Fokwa, Boniface P. T. ( May 2020 , Angewandte Chemie)

   Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V₃B₄have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 mH₂SO₄) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm⁻²current density) and −0.273 mV (for V₃B₄) we accurately predict the overpotential of VB₂(−0.204 mV) as well as that of unstudied V₂B₃(−0.250 mV) and hypothetical “V₅B₈” (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical V_xB_yphases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships.

    

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2. Multi‐Interface‐Modulated CoS 2 @MoS 2 Nanoarrays Derived by Predesigned Germanomolybdate Polymer Showing Ultrahighly Electrocatalytic Activity for Hydrogen Evolution Reaction in Wide pH Range

   https://doi.org/10.1002/admi.202000780  

   Hou, Yan ; Pang, Haijun ; Xin, Jianjiao ; Ma, Huiyuan ; Li, Bonan ; Wang, Xinming ; Tan, Lichao ( August 2020 , Advanced Materials Interfaces)

   The development of non‐noble metal materials for efficient hydrogen evolution reaction (HER) in wide pH range is still a challenge at present. Herein, a predesigned polyoxometalate (POM)‐based metal–organic polymer {L₃Co₂ · 6H₂O}[H₃GeMo₁₂O₄₀] · 9H₂O (L = 1,2,4‐triazole) is employed as bimetallic source together with thiourea converting to CoS₂@MoS₂on carbon cloth (CC) (abbreviated to CoS₂@MoS₂@CC) for the first time. Impressively, the CoS₂@MoS₂in the form of vertically interconnected nanoarrays with multiple interfaces are grown in situ on CC and act as electrodes directly for HER. The CoS₂@MoS₂@CC‐30h composite exhibits superb activity and long‐durability in both acidic and alkaline media. Low overpotential is achieved in 0.5mH₂SO₄(65 mV) and 1.0mKOH (87 mV) for 10 mA cm⁻²versus RHE, which overmatch major MoS₂‐/POM‐based electrocatalysts. This work therefore may shed substantial lights on designing active and durable molybdenum‐based bi‐/polymetallic sulfide from variable POM‐based metal–organic polymers for electrocatalytic hydrogen evolution reaction in wide pH range.

    

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3. Canonic‐Like HER Activity of Cr 1– x Mo x B 2 Solid Solution: Overpowering Pt/C at High Current Density

   https://doi.org/10.1002/adma.202000855  

   Park, Hyounmyung ; Lee, Eunsoo ; Lei, Ming ; Joo, Hyunkeun ; Coh, Sinisa ; Fokwa, Boniface P. T. ( June 2020 , Advanced Materials)

   Abundant transition metal borides are emerging as substitute electrochemical hydrogen evolution reaction (HER) catalysts for noble metals. Herein, an unusual canonic‐like behavior of theclattice parameter in the AlB₂‐type solid solution Cr_1–xMo_xB₂(x= 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) and its direct correlation to the HER activity in 0.5 M H₂SO₄solution are reported. The activity increases with increasingx, reaching its maximum atx= 0.6 before decreasing again. At high current densities, Cr_0.4Mo_0.6B₂outperforms Pt/C, as it needs 180 mV less overpotential to drive an 800 mA cm⁻²current density. Cr_0.4Mo_0.6B₂has excellent long‐term stability and durability showing no significant activity loss after 5000 cycles and 25 h of operation in acid. First‐principles calculations have correctly reproduced the nonlinear dependence of theclattice parameter and have shown that the mixed metal/B layers, such as (110), promote hydrogen evolution more efficiently forx= 0.6, supporting the experimental results.

    

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4. Basal Plane Hydrogen Evolution Activity from Mixed Metal Nitride MXenes Measured by Scanning Electrochemical Microscopy

   https://doi.org/10.1002/adfm.202001136  

   Djire, Abdoulaye ; Wang, Xiang ; Xiao, Chuanxiao ; Nwamba, O. Charles ; Mirkin, Michael V. ; Neale, Nathan R. ( May 2020 , Advanced Functional Materials)

   2D early transition metal carbide and nitride MXenes have intriguing properties for electrochemical energy storage and electrocatalysis. These properties can be manipulated by modifying the basal plane chemistry. Here, mixed transition metal nitride MXenes, M‐Ti₄N₃T_x(M = V, Cr, Mo, or Mn; T_x= O and/or OH), are developed by modifying pristine exfoliated Ti₄N₃T_xMXene with V, Cr, Mo, and Mn salts using a simple solution‐based method. The resulting mixed transition metal nitride MXenes contain 6–51% metal loading (cf. Ti) that exhibit rich electrochemistry including highly tunable hydrogen evolution reaction (HER) electrocatalytic activity in a 0.5mH₂SO₄electrolyte as follows: V‐Ti₄N₃T_x> Cr‐Ti₄N₃T_x> Mo‐Ti₄N₃T_x> Mn‐Ti₄N₃T_x> pristine Ti₄N₃T_xwith overpotentials as low as 330 mV at −10 mA cm⁻²with a charge‐transfer resistance of 70 Ω. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M‐Ti₄N₃T_xas well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications.

    

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5. Asymmetric Active Sites for Boosting Oxygen Evolution Reaction

   https://doi.org/10.1002/smll.202304108  

   Han, Linkai ; Yu, Haifeng ; Xiang, Zhonghua ( June 2023 , Small)

   Transition metal‐nitrogen‐carbon materials with atomically dispersed active sites are promising catalysts for oxygen evolution reaction (OER) since they combine the strengths of both homogeneous and heterogeneous catalysts. However, the canonically symmetric active site usually exhibits poor OER intrinsic activity due to its excessively strong or weak oxygen species adsorption. Here, a catalyst with asymmetric MN₄sites based on the 3‐s‐triazine of g‐C₃N₄(termed as a‐MN₄@NC) is proposed. Compared to symmetric, the asymmetric active sites directly modulate the oxygen species adsorption via unifying planar and axial orbitals (dx²‐y², dz²), thus enabling higher OER intrinsic activity. In Silico screening suggested that cobalt has the best OER activity among familiar nonprecious transition metal. These experimental results suggest that the intrinsic activity of asymmetric active sites (179 mV overpotential at onset potential) is enhanced by 48.4% compared to symmetric under similar conditions. Remarkably, a‐CoN₄@NC showed excellent activity in alkaline water electrolyzer (AWE) device as OER catalyst, the electrolyzer only required 1.7 V and 2.1 V respectively to reach the current density of 150 mA cm⁻²and 500 mA cm⁻². This work opens an avenue for modulating the active sites to obtain high intrinsic electrocatalytic performance including, but not limited to, OER.

    

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