Abstract-This paper presents an overview of the theory and currently known techniques for multi-cell MIMO (multiple input multiple output) cooperation in wireless networks. In dense networks where interference emerges as the key capacitylimiting factor, multi-cell cooperation can dramatically improve the system performance. Remarkably, such techniques literally exploit inter-cell interference by allowing the user data to be jointly processed by several interfering base stations, thus mimicking the benefits of a large virtual MIMO array. Multicell MIMO cooperation concepts are examined from different perspectives, including an examination of the fundamental information-theoretic limits, a review of the coding and signal processing algorithmic developments, and, going beyond that, consideration of very practical issues related to scalability and system-level integration. A few promising and quite fundamental research avenues are also suggested.

Thin-film solid oxide fuel cell ͑SOFC͒ structures containing electrolyte membranes 50-150 nm thick were fabricated with the help of sputtering, lithography, and etching. The submicrometer SOFCs were made of yttria-stabilized zirconia ͑YSZ͒ or YSZ/ gadolinium-doped ceria composites electrolyte and 80 nm porous Pt as cathode and anode. The peak power densities were 200 and 400 mW/cm 2 at 350 and 400°C, respectively. The high power densities achieved are not only due to the reduction of electrolyte thickness but also to the high charge-transfer reaction rates at the interfaces between the nanoporous electrodes ͑cathode and/or anode͒ and the nanocrystalline thin electrolyte.

Developing anodic oxygen evolution reaction (OER) electrocatalysts with high catalytic activities is of great importance for effective water splitting. Compared with the water‐oxidation electrocatalysts that are commonly utilized in alkaline conditions, the ones operating efficiently under neutral or near neutral conditions are more environmentally friendly with less corrosion issues. This review starts with a brief introduction of OER, the importance of OER in mild‐pH media, as well as the fundamentals and performance parameters of OER electrocatalysts. Then, recent progress of the rational design of electrocatalysts for OER in mild‐pH conditions is discussed. The chemical structures or components, synthetic approaches, and catalytic performances of the OER catalysts will be reviewed. Some interesting insights into the catalytic mechanism are also included and discussed. It concludes with a brief outlook on the possible remaining challenges and future trends of neutral or near‐neutral OER electrocatalysts. It hopefully provides the readers with a distinct perspective of the history, present, and future of OER electrocatalysts at mild conditions.

This study establishes an approach to 3D print Li‐ion battery electrolytes with controlled porosity using a dry phase inversion method. This ink formulation utilizes poly(vinyldene fluoride) in a mixture of N‐methyl‐2‐pyrrolidone (good solvent) and glycerol (weak nonsolvent) to generate porosity during a simple drying step. When a nanosized Al2O3 filler is included in the ink, uniform sub‐micrometer pore formation is attained. In other words, no additional processing steps such as coagulation baths, stretching, or etching are required for full functionality of the electrolyte, which makes it a viable candidate to enable completely additively manufactured Li‐ion batteries. Compared to commercial polyolefin separators, these electrolytes demonstrate comparable high rate electrochemical performance (e.g., 5 C), but possess better wetting characteristics and enhanced thermal stability. Additionally, this dry phase inversion method can be extended to printable composite electrodes, yielding enhanced flexibility and electrochemical performance over electrodes prepared with only good solvent. Finally, sequentially printing this electrolyte ink over a composite electrode via a direct write extrusion technique has been demonstrated while maintaining expected functionality in both layers. These ink formulations are an enabling step toward completely printed batteries and can allow direct integration of a flexible power source in restricted device areas or on nonplanar surfaces.

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In this study, atomic layer deposition (ALD) was used to deposit Pt thin films as an electrode/catalyst layer for solid oxide fuel cells. I−V measurements were performed to determine the dependence of the fuel cell performance on the Pt film thickness at different operating temperatures. The measured fuel cell performance revealed that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the platinum loading relative to dc-sputtered Pt anodes. The Pt films fabricated by dc sputtering and ALD had different microstructure, which accounted for the difference in their performance as a fuel cell anode. In addition to the continuous electrocatalyst layer, a micropatterned Pt structure was fabricated via area-selective ALD and used as a current collector grid/patterned catalyst for the fuel cells. An improvement of the fuel cell performance by a factor of 10 was observed using the Pt current collector grid/patterned catalyst integrated onto cathodic La0.6Sr0.4Co0.2Fe0.8O3-δ. The study suggests the potential to achieve improved performance and/or lower loadings using ALD for catalysts in fuel cells.

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Electrocatalysis has emerged as an attractive way for artificial CO2 fixation to CH3OH, but the design and development of metal‐free electrocatalyst for highly selective CH3OH formation still remains a key challenge. Here, it is demonstrated that boron phosphide nanoparticles perform highly efficiently as a nonmetal electrocatalyst toward electrochemical reduction of CO2 to CH3OH with high selectivity. In 0.1 m KHCO3, this catalyst achieves a high Faradaic efficiency of 92.0% for CH3OH at −0.5 V versus reversible hydrogen electrode. Density functional theory calculations reveal that B and P synergistically promote the binding and activation of CO2, and the rate‐determining step for the CO2 reduction reaction is dominated by *CO + *OH to *CO + *H2O process with free energy change of 1.36 eV. In addition, CO and CH2O products are difficultly generated on BP (111) surface, which is responsible for the high activity and selectivity of the CO2‐to‐CH3OH conversion process.