Regulating local charges of atomically dispersed Moδ+ sites by nitrogen coordination on cobalt nanosheets to trigger water dissociation for boosted hydrogen evolution in alkaline media

Now,Pt-based materials are still the best catalysts for hydrogen evolution reaction(HER).Nevertheless,the scarcity of Pt makes it impossible for the large-scale applications in industry.Although cobalt is taken as an excellent HER catalyst due to its suitable H*binding,its alkali HER catalytic property need to be improved because of the sluggish water dissociation kinetics.In this work,nitrogen with small atomic radius and metallophilicity is employed to adjust local charges of atomically dispersed Mo^(δ+)sites on Co nanosheets to trigger water dissociation.Theoretical calculations suggest that the energy barrier of water dissociation can be effectively reduced by introducing nitrogen coordinated Mo^(δ+)sites.To realize this speculation,atomically dispersed Mo^(δ+)sites with nitrogen coordination of Mo(N)/Co were prepared via reconstruction of CoMoO_(4).High angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)and X-ray absorption spectroscopy(XAS)demonstrate the coordination of N atoms with atomically dispersed Mo atoms,leading to the local charges of atomically dispersed Mo^(δ+)sites in Mo(N)/Co.The measurement from ambient pressure X-ray photoelectron spectroscopy(AP-XPS)reveals that the Mo^(δ+)sites promote the adsorption and activation of water molecule.Therefore,the Mo(N)/Co exhibits an excellent activity,which need only an overpotential of 39 mV to reach the current density of 10 mA cm^(-2).The proposed strategy provides an advance pathway to design and boost alkaline HER activity at the atomic-level.

Cu纳米针上电场促进C-C耦合增强CO_(2)电还原生成C_(2)产物

电催化CO_(2)减排技术利用电能将过量的CO_(2)转化为有附加值的化学品,是解决能源危机、实现碳中和的有效途径之一.电催化CO_(2)还原反应(CO_(2)RR)中的多碳产物(C_(2)),如乙烯和乙醇,因其比C1产物具有更高的能量密度和更广泛的应用而受到较大关注.目前为止,Cu基催化剂被认为是获得C_(2)产物的独特材料.研究者在提高Cu基催化剂C_(2)产物的活性和选择性方面做了大量的工作,如催化剂形貌工程、活性位点设计和中间吸附性能调控等.许多理论和实验研究已经证明,Cu基催化剂上的C-C偶联过程是C_(2)产物生成的速率决定步骤.优化C-C偶联过程的能垒是提高C_(2)产物活性和选择性的重要而直接的策略.CO_(2)RR在Cu上是由CO_(2)还原吸附CO(*CO)并二聚生成C_(2)产物引起的.C-C偶联过程与*CO的吸附性能密切相关.众所周知,CO是一种典型的极性分子,因此其在催化剂表面的吸附性能可能会受到活性位点周围的局部电场的影响.构建合适的局部电场是调节CO吸附性能和C-C偶联过程的潜在手段之一.前期工作(Nature,2016,537,382-386)证明了高曲率金纳米针可以在尖端产生高的局部电场.高局域电场诱导K+聚集,使活性位点周围CO_(2)浓度升高,大大促进了Au纳米针上的CO生成.基于Au纳米针的局域电场促进了CO_(2)RR的CO生成.本文利用Cu纳米针促进并优化C-C偶联反应来提高C_(2)产物活性和选择性.结果表明,局部电场可以促进C-C偶联过程,进而增强CO_(2)电还原生成C_(2)产物.有限元模拟结果表明,高曲率铜纳米针处存在较强的局部电场;密度泛函理论计算结果表明,强电场能促进C-C耦合过程.在此基础上,制备了一系列不同曲率的Cu催化剂,其中,Cu纳米针(CuNNs)的曲率最高,Cu纳米棒(CuNRs)和Cu纳米颗粒(CuNPs)曲率次之.实验测得CuNNs上吸附的K+浓度最高,证明了纳米针上的局部电场最强.同时,CO吸附传感器测试表明,CuNNs对CO的吸附能力最强,原位傅里叶变换红外光谱显示,CuNNs的*COCO和*CO信号最强.由此可见,高曲率铜纳米针可以诱导高局部电场,从而促进C-C耦合过程.催化性能测试结果表明,在低电位(-0.6 V vs.RHE)下,Cu NNs对CO_(2)RR的生成C_(2)产物的法拉第效率值为44%,约为Cu NPs的2.2倍.综上,本文为CO_(2)RR过程中提高多碳产物提供了新的思路.

Sequential reactant water management by complementary multisite catalysts for surpassing platinum hydrogen evolution activity

Alkaline hydrogen evolution reaction(HER)offers a near-zero-emission approach to advance hydrogen energy.However,the activity limited by the multiple reaction steps involving H_(2)O molecules transfer,absorption,and activation still unqualified the thresholds of economic viability.Herein,we proposed a multisite complementary strategy that incorporates hydrophilic Mo and electrophilic V into Ni-based catalysts to divide the distinct steps on atomically dispersive sites and thus realize sequential regulation of the HER process.The Isotopic labeled in situ Raman spectroscopy describes 4-coordinated hydrogen bonded H_(2)O to be free H_(2)O passing the inner Helmholtz plane in the vicinity of the catalysts under the action of hydrophilic Mo sites.Furthermore,potential-dependent electrochemical impedance spectroscopy(EIS)reveals that electrophilic V sites with abundant 3d empty orbitals could activate the lone-pair electrons in the free H_(2)O molecules to produce more protic hydrogen,and dimerize into H_(2) at the Ni sites.By the sequential management of reactive H_(2)O molecules,NiMoV oxides multisite catalysts surpass Pt/C hydrogen evolution activity(49 mV@10 mA∙cm^(-2) over 140 h).Profoundly,this study provides a tangible model to deepen the comprehension of the catalyst–electrolyte interface and create efficient catalysts for diverse reactions.

外场驱动分子极化调控反应物界面及其电催化析氢性能

反应物界面对电催化反应至关重要.然而,由于调控和表征手段的不足,对反应物界面的深入研究仍难以实现.本文中,我们借助单片电催化微纳器件,通过调节背栅电压引入分子极化,实现了对电化学双电层中水合氢离子(H_(3)O^(+))浓度的调控,进而提高了催化剂的电催化析氢性能.以C_(60)/MoS_(2)异质结为例,电学性能测试表明背栅电场促进了电子从C_(60)向MoS_(2)的转移,并导致了C_(60)分子的极化.原位光致发光光谱表征显示,在背栅电场的作用下,极化的C_(60)分子会吸引H_(3)O^(+),使其聚集在MoS_(2)附近.而电催化测试表明,在1.5 V背栅电压下,由于发生了H_(3)O^(+)的富集,C_(60)/MoS_(2)异质结在-0.45 VRHE电位下的析氢电流密度增加了5倍我们提出的调控和监测反应物界面的方法能够促进对多种电催化反应的研究.

Graphitic carbon nitride based single-atom photocatalysts

Single-atom photocatalysts,due to their high catalysis activity,selectivity and stability,become a hotspot in the field of photocatalysis.Graphitic carbon nitride(g-C3N4)is known as both a good support for single atoms and a star photocatalyst.Developing g-C3N4-based single-atom photocatalysts exhibits great potential in improving the photocatalytic performance.In this review,we summarize the recent progress in g-C3N4-based single-atom photocatalysts,mainly including preparation strategies,characterizations,and their photocatalytic applications.The significant roles of single atoms and catalysis mechanism in g-C3N4-based single-atom photocatalysts are analyzed.At last,the challenges and perspectives for exploring high-efficient g-C3N4-based single-atom photocatalysts are presented.