Tuning a semiconductor to function as a fast proton conductor is an emerging strategy in the rapidly developing field of proton ceramic fuel cells (PCFCs). The key challenge for PCFC researchers is to formulate the proton-conducting electrolyte with conductivity above 0.1 siemens per centimeter at low temperatures (300 to 600°C). Here we present a methodology to design an enhanced proton conductor by means of a NaxCoO2/CeO2 semiconductor heterostructure, in which a field-induced metallic state at the interface accelerates proton transport. We developed a PCFC with an ionic conductivity of 0.30 siemens per centimeter and a power output of 1 watt per square centimeter at 520°C. Through our semiconductor heterostructure approach, our results provide insight into the proton transport mechanism, which may also improve ionic transport in other energy applications.

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Surface nuclear magnetic resonance (NMR) is emerging as a competitive method for aquifer exploration due to its direct sensitivity to subsurface water, but the method still has several shortcomings, for example, a signal-to-noise ratio that is often poor, long survey times, and bulky equipment. We have developed Apsu, a new surface NMR system designed for near-surface groundwater investigations. It provides several features such as a compact transmitter unit, separated, small receiver coils, wireless connections between multiple receivers, quasi-zero dead time, and robust phase determination. The transmitter unit is powered by a lightweight generator, and it drives a triangular current in an untuned [Formula: see text] transmitter coil. The peak current of the triangular waveform is up to 145 A, with an effective peak current of 105 A at a Larmor frequency of 2 kHz, corresponding to a 30 m depth of investigation. The frequency and amplitude in each half-oscillation of the transmit pulses can be modulated independently, which gives great flexibility in the pulse design. The receiver uses low-noise preamplifiers and multiple receivers linked to a central unit through Wi-Fi. The use of small receiver coils and wireless connections to multichannel receivers greatly improves the layout configuration flexibility and survey efficiency. The performance of the system under field conditions is demonstrated with high-quality data collected near Silkeborg, Denmark, using on-resonance and numerically optimized modulation pulses.

Aquifer properties can be obtained from envelopes of surface nuclear magnetic resonance (NMR) signals, but this demands high-quality data. To retrieve reliable envelopes using synchronous detection from the intrinsically low signal-to-noise ratio (SNR) surface NMR recordings, a variety of signal processing techniques are employed to mitigate noise. We present a different approach to retrieve complex envelopes using spectral analysis and a sliding window, which can potentially improve SNR significantly. The complex envelope is composed of the spectral values at the Larmor frequency found through the Fourier transform of surface NMR data using a sliding window. We discuss how to maximize the SNR of envelope by selecting the optimum length and shape of the sliding window. An accompanying method for determining the Larmor frequency is presented and we address how noise can deteriorate the envelope retrieval in spectral analysis. Results obtained from synthetic models and field measurements in low and high noise environments reveal that the proposed method not only improves the accuracy and efficiency of envelope retrieval, but also eliminates the transient distortion of early-time signal caused by the filtering procedure.

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