• Energy Research

AbstractElectrochemical water splitting has attracted considerable attention for the production of hydrogen fuel by using renewable energy resources. However, the sluggish reaction kinetics make it essential to explore precious‐metal‐free electrocatalysts with superior activity and long‐term stability. Tremendous efforts have been made in exploring electrocatalysts to reduce the energy barriers and improve catalytic efficiency. This review summarizes different categories of precious‐metal‐free electrocatalysts developed in the past 5 years for alkaline water splitting. The design strategies for optimizing the electronic and geometric structures of electrocatalysts with enhanced catalytic performance are discussed, including composition modulation, defect engineering, and structural engineering. Particularly, the advancement of operando/in situ characterization techniques toward the understanding of structural evolution, reaction intermediates, and active sites during the water splitting process are summarized. Finally, current challenges and future perspectives toward achieving efficient catalyst systems for industrial applications are proposed. This review will provide insights and strategies to the design of precious‐metal‐free electrocatalysts and inspire future research in alkaline water splitting.

Abstract Wide–scale commercialisation of proton exchange membrane fuel cell (PEMFC) is hindered by the degradation of cathode catalyst and carbon support, making it crucial to understand these mechanisms. This study compares the cathode catalyst and carbon support degradations mechanisms using commercial gas diffusion electrode in operating PEMFCs. The impact of the accelerated stress tests (ASTs) is monitored by recording the polarisation, electrochemical surface area (ECSA) and mass activity. Furthermore, the electrochemical impedance spectroscopy (EIS) is monitored at seven operating points from 0.05 to 1 A cm−2. For both phenomena, the charge transfer resistance increases at high current densities, which is attributed to the losses in activity observed with the ECSA and the mass activity degradations. In the carbon–corroded PEMFC, the mass transport resistance first reduces by 45% (0–100 cycles), suggesting an increase in electrode porosity due to carbon corrosion. At a later stage (200–5000 cycles), the mass transport resistance increases by 225% as the electrode collapses. On the other hand, in the catalyst–degraded PEMFC, the mass transport resistance uniformly reduces while the charge transfer resistance increases by 30%. Altogether, EIS provides additional sensitivity to differentiate catalyst and carbon support degradation within PEMFCs.

The inherent short‐term transience of renewable energy sources causes significant challenges for the electricity grids. Energy storage systems that can simultaneously provide high power and high energy efficiency are required to accommodate the intermittent renewables. Herein, an ultrafast and high‐capacity aqueous proton battery is developed based on the organic pyrene‐4,5,9,10‐tetraone (PTO) anode. The co‐insertion of H2O molecules and proton into the PTO organic anode effectively reduces the interfacial resistance between the anode and electrolytes, and achieves an unprecedented rate capability up to 250 C and as short as 7 s per charge/discharge. A PTO‐based full cell exhibits an outstanding power density (>104 W kg−1) comparable to supercapacitors. The full utilization of the four C=O groups in PTO molecule during cycling enables the highest capacity (85 mAh g−1) reported for proton batteries to date. This study represents a significant leap forward in the exploitation of ultrafast electrochemical energy storage and accelerates the development of intermittent grid‐scale energy storage technologies.

The catalytic active sites of NiFe and NiFeCr (oxy)hydroxides are revealed byoperandospectroscopic techonologies for alkaline water oxidation.

Abstract In order to achieve a perfect bottom-up electroplated Cu filling with a minimal surface thickness, 2-mercaptopyridine (2-MP) was investigated as a new leveler for replacing Janus Green B (JGB) for bottom-up copper filling. Electrochemical impedence results indicate that 2-MP has a stronger suppression for Cu deposition than JGB. With the addition of 2-MP, the filling capability of the electroplating solution is improved significantly with the Cu thickness on surface decreasing from ∼16 μm to ∼10 μm. The interaction mechanisms of 2-MP, bis(3-sulfopropyl) disulfide (SPS), Cl − and tri-block copolymer of PEG and PPG with ethylene oxide terminal blocks (EPE) in the plating solution are studied by galvanostatic measurements (GMs). The acceleration effect of SPS and the inhibition effect of 2-MP on copper deposition occur in the presence of EPE, and the convection-dependent adsorption (CDA) behavior of additives usually occurs with the injection of four additives at optional concentrations. Further, it was found that when 1.0 ppm 2-MP, 1.0 ppm SPS and 200 ppm EPE were injected into the basic electrolyte, the potential difference ( Δ h) value of the electrolyte became positive, and the bottom-up electroplated copper filling was obtained in the electrolyte in absence of Cl − . The interaction mechanisms of three additives for bottom-up filling have been investigated by GMs.

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO2 reduction, and N2 reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.

The degradation mechanisms of Fe–N–C catalysts in hydrogen fuel cells are deconvoluted using operando electrochemical methods.

Various efficient and convenient strategies have been investigated to design carbon-based catalysts for electrochemical CO2 reduction.

Ammonia (NH3), a carbon-free hydrogen carrier, is an important commodity for the food supply chain owing to its high energy capacity and ease of storage and transport. The Haber–Bosch process is currently the favored industrial method for large-scale ammonia production but requires energy-intensive and sophisticated infrastructure which hampers its utilization in a sustainable and decentralized system of manufacture. The electrochemical nitrogen reduction reaction (eNRR) at ambient conditions holds great potential for sustainable production of ammonia using electricity generated from renewable energy sources such as solar and wind. However, this approach is limited by a low rate of ammonia production with high overpotential and the competing hydrogen evolution reaction (HER). For a better understanding and utilization of eNRR as a sustainable process, insight into rational catalyst design and mechanistic evaluations by a theoretically-directed experimental approach is imperative. Herein, recent insights into rational catalyst design and mechanisms, based on intrinsic and extrinsic catalytic activity are articulated. Following the elucidation of basic principles and mechanisms, a framework supplied by theoretical studies that lead to the optimal selection and development of eNRR catalysts is presented. Following a discussion of recently developed electrocatalysts for eNRR, we outline various recently-used theoretical and experimental methodologies to improve the intrinsic and extrinsic catalytic activity of advanced electrocatalysts. This review is anticipated to contribute to the development of active, selective, and efficient catalysts for nitrogen reduction.